M5 Running Issues

Specific conversations and info for the BMW E28 M5 and M535i.
MattyCV
Posts: 63
Joined: Jul 21, 2017 11:54 AM
Location: Seattle

M5 Running Issues

Post by MattyCV »

Hello everyone!

My first time posting in this sub-thread. I’ve owned a 528e (and still do) but recently added a 1988 M5 to my garage. I’m loving it so far; when it comes over 4K RPM, there is nothing like it!

Anyway, my car IS having some issues that I’d like to attempt to narrow down before I bring it to a shop. What it’s doing is really odd. Sometimes, the acceleration is very ferocious and kicks you back into the seat. But other times, it revs up to redline but feels like it’s barely accelerating at all? It’s a hard sensation to describe. It’s like it’s just revving but not going anywhere. A problem that *could* go with this is that the throttle sometimes sticks under any load. I’ll have to rev it to get it to go back to normal idle.

My first thought is a throttle cable, but it could also have something to do with the ITB’s? I’ve never owned a car with them before so I’m not familiar. Another thing I might add is that the previous owner swapped in a head from a 3.6 E34 M5 but I don’t think there is a MAF installed, just the standard AFM. I suppose it could be something with that too, but I really don’t know. It has aftermarket euro headers as well.

Has anyone else had this issue before? I’ve searched and searched but never found any situation similar to this. Idle is perfect and it never stumbles.

I appreciate any help I can get. Thank you! And happy to be a part of the M family now - with the best M car.

*Edit: this happens randomly, not all the time. There doesn’t seem to be a pattern, it just does it whenever it wants. Not sure if this is any help but figured I’d add it. And yes, the car does still move so I don’t think it’s transmission or diff slip, it definitely feels throttle related.
austin8753
Posts: 1444
Joined: May 16, 2010 1:37 AM
Location: Portland, Oregon, USA

Re: M5 Running Issues

Post by austin8753 »

I had a similar issue with my M5 a few months ago. Installed a set of injectors that I thought were compatible, but they weren't. You might check to see if yours has the correct Bosch "201" units installed. I would still definitely suggest having them rebuilt.

Additionally, it would be worth checking the condition of your cap and rotor (also making sure there is no moisture in the cap), testing the blue coolant temperature sensor and the oxygen sensor, inspecting the spark plugs, etc.

Good luck, I really hope you are able to figure it out.
Randomg
Posts: 480
Joined: Jul 12, 2007 3:12 PM
Location: Seattle

Re: M5 Running Issues

Post by Randomg »

I've had the sticky throttle problem caused by a sticky idle air control valve and misadjusted (or broken) throttle position sensor working in tandem. The sticky ICV makes for holding a high idle, the WOT not triggering the ECU into idle mode causes the engine to keep spraying fuel. When the TPS is functioning correctly, and you're off the throttle, the ECU will cut fuel above what I remember as... 1200 rpm for the s38, and it will override a sticky ICV.

A misadjusted or failed TPS would also cause your acceleration problem, as the ECU would not go into full throttle mode as it should, and you'd be stuck in efficiency mode at full throttle.

Another possibility is an actually stuck throttle cable, which I've had happen before as well, but at least in my case, it wasn't intermittent. Since your problem is intermittent, I would lean towards the TPS, since it would also be the cause of both the sticky idle and acceleration problem.

Throttle linkage could cause your idle problem, but in my experience not your acceleration problem.

Edit: also I live in Seattle now, so feel free to pm me and maybe I could help in person.
MattyCV
Posts: 63
Joined: Jul 21, 2017 11:54 AM
Location: Seattle

Re: M5 Running Issues

Post by MattyCV »

Austin - I'll definitely have to check that out. I haven't checked my cap and rotor yet so the car is probably in need of a tune up regardless. Injectors will be rebuilt once I have a second car and can justify not having the car on the road for a couple weeks (they'd be sent out). I'm a mad man having a 32 year old M5 as my only car but hey, it keeps life exciting. :D

Randomg - those are interesting ideas, too. From what it sounds like, that could definitely be a culprit. How would I go about checking those items? Ohmmeter? I wonder if it'd give an indication without the issue presenting itself, as it never does the problem when just idling. It only seems to want to do it when it's under load.

I appreciate the help I've gotten from both of you so far. The shop I took it to was saying that they'd have to rebuild every single one of my throttle bodies for a price of $1000 - just for labor! They couldn't even quote me on parts. I went home and played with them a bit, pressing the throttle and moving the throttle linkage (with the car off) and it NEVER stuck or gave me any indication of it. The only thing I could see requiring maintenance is the throttle linkage itself, as that controls the ITB's, but the ITB's themselves? I'm not so sure. They were also telling me that a charge for fixing an oil filter leak is almost $700...like, what? I knew this car would be expensive but that just seems like a joke. Even a brand new housing is 1/6 of that. That's when I became a bit skeptical.

I just wanted to make sure that there might be another culprit because the diagnosis they gave is iffy to me. I'm happy to be aware that there are other things to check before diving into that rabbit hole.

And to Randomg - I actually moved from Seattle to Raleigh, NC for work. I'll be back on the West sometime and could say hello. I appreciate the offer nonetheless! :cool:

Edit: if it helps, when the throttle does stick, the throttle will sometimes like to start to rev up a bit. It doesn't just stay at one specific RPM constantly. And even if I rev it up a tad, it'll go to that new position I revved it to, and then I have to give it a LOT of gas to get it to go away. I've just started to notice that and figured it'd be good info to add.
Preyupy
Posts: 326
Joined: Jun 21, 2012 12:48 AM
Location: Issaquah WA

Re: M5 Running Issues

Post by Preyupy »

Are you sure your throttles are sticking? It could also be your Idle Speed control valve. If your throttle position switch is not adjusted correctly you can get a high idle with a stuck idle valve. If the idle goes up over 1350 rpm with the TPS in the closed throttle position the engine should “lope” as the injectors should shut off and then come back on at about 1250 rpm and just keep cycling like that.
MattyCV
Posts: 63
Joined: Jul 21, 2017 11:54 AM
Location: Seattle

Re: M5 Running Issues

Post by MattyCV »

Preyupy - it doesn’t go up and down like that at idle. I think I’m going to try to clean my idle valve today though, since the problem seems to be getting worse.

Now, the car does not like to come down from revs at all. It’s so odd. When I shift, they come down very, very slowly and make shifting hard since the RPM’s might be too high. Also, if I rev it up at idle it’ll almost want to stick to the RPM it went to. When I turn the car back on after it’s idling at 1k or above, it’s back to normal idle speed. I opened the hood and nothing physical appears to be sticking.

Does this almost definitely mean my TPS is bad and needs to be replaced?
Preyupy
Posts: 326
Joined: Jun 21, 2012 12:48 AM
Location: Issaquah WA

Re: M5 Running Issues

Post by Preyupy »

The TPS is easy to test. Use an ohm meter, remove the connector, at closed throttle the center pin will be connected to one of the outer pins, at full throttle it should connect to the other, at part throttle there should be no contact. You should even be able to hear it click. If the ICV is sticking you can easily see this problem, a quick check is when it is acting up reach into the Valve and clamp off one of the hoses with pliers. If the RPM drops immediately you have a problem with the valve, if not you might have a vacuum leak or something going on with the throttle plates and/or cable. With the engine off when you open the throttle by hand and let go does it snap back to the stop? Now try the same thing using the throttle pedal.
MattyCV
Posts: 63
Joined: Jul 21, 2017 11:54 AM
Location: Seattle

Re: M5 Running Issues

Post by MattyCV »

Based on the fact that my TPS part number ends in "319" vs. the RealOEM specified 277/301, I assume that it's at least in need of replacement. I actually looked up the part number I have on and people were having issues with it, so at least that will be sorted. I ordered one because nearly every site I was looking at had NLA next to it, so I just bought one off ECS and will see if it fixes it.

I'll test my ICV today, too. It might be teaming up with the TPS, as Randomg was saying. I wish it wasn't in such a hard location to access. :x My 528e has it right in front of you. A simple clean is harder than I would have thought on this car.

I honestly did think it was the throttle cable, but because it's so sporadic, I don't think it'd be that. I've played with the linkage and gas pedal and looked and it does not stick - and it ALWAYS goes right back to the full stop - doesn't stop halfway in between, etc. The fact that I can turn the car on and off and the symptom goes away tells me it has nothing to do with it. When it's acting up, it's ALSO randomly revving the engine so I have to put it in neutral when I come to a stop so it doesn't jolt me forward. Then when I come to a stop? It goes right back down to normal idle speed.

I'd rather replace the ICV than clean, if that's truly what is messing with some things - but it's backordered. :cry: Is it a good idea to even try to find a used one on the forum? I assume this part is notorious for acting up so buying used doesn't seem like the best idea. It seems like most owners just clean it as a normal maintenance item?
Preyupy
Posts: 326
Joined: Jun 21, 2012 12:48 AM
Location: Issaquah WA

Re: M5 Running Issues

Post by Preyupy »

If the ICV on your 528e is working you can put it on the M5 just to test the theory before you spend $200, they are the same unit
Last edited by Preyupy on Mar 19, 2020 1:57 AM, edited 1 time in total.
Randomg
Posts: 480
Joined: Jul 12, 2007 3:12 PM
Location: Seattle

Re: M5 Running Issues

Post by Randomg »

Edit: if it helps, when the throttle does stick, the throttle will sometimes like to start to rev up a bit. It doesn't just stay at one specific RPM constantly. And even if I rev it up a tad, it'll go to that new position I revved it to, and then I have to give it a LOT of gas to get it to go away. I've just started to notice that and figured it'd be good info to add.
Those exact symptoms have happen to me after messing with my ICV and TPS. Cleaning the ICV again and redoing the TPS adjustment made it go away. It's possible that when I took the throttles off again, whatever had caused them to stick/bind I fixed as well.

ICVs are pretty reliable. The things that can keep them from functioning is if they get dirty and the door gets stuck. A good clean should be all you need. I think on start up the ICV tries to go to full open, so full voltage on startup that unsticks it might be why it always works after a restart. On the TPS, based on your complaints of both WOT and idle not working consistently, would lead me to just go ahead and replace it.

One more thing before you go replacing/taking things apart. Does it happen when cold? Open the hood before your next drive and press on the linkage to open and close the throttles. Do you hear the click from the TPS when it comes to a stop (like it should). Then next time the problem happens, turn the car off, open the hood, and press on the throttle linkage to open and close them, and listen for the click from the TPS. If you can hear it when cold but not when hot, it could be the TPS, it could be the throttles getting hot, expanding, and then coming to rest on some gunk on the throttle wall instead of the stopper. I've not had the throttle linkage ever give me trouble, so I suspect TPS needs to be replaced, or at least adjusted to make sure it clicks when the car's warmed up. Also make sure the TPS plug is all the way in and locked with that little metal clip.
MattyCV
Posts: 63
Joined: Jul 21, 2017 11:54 AM
Location: Seattle

Re: M5 Running Issues

Post by MattyCV »

I finally got to stop the car when it was having issues. I got the chance to take a video of the car. This is the car at operating temp. You can hear the revs drop dramatically (it was idling at 1500 and came down to 7-800). Does this mean my linkage itself is messed up? I’ve linked a video below on YouTube.

https://youtu.be/1UmH_2e5-Ho

You can also hear a click coming from somewhere - possibly the linkage? I don’t even know what parts to start getting to work on something like this. It doesn’t seem like the TPS or ICV would be making it stick like that, as it looks to be mechanically challenged, right? I’m stumped at where to start with this, but I’m happy I have a video!

I’m still not entirely sure it’s the main problem. If it does stick in that position, why would it go away sometimes after coming to a stop, or jolt the car forward randomly when it sticks? Or, when the idle is consistent at 3-5k RPM, why would only that amount of stick amount to that many revs or it slowly coming down? While I know there’s something weird with this area now, it still seems like there could be more to the story.
Preyupy
Posts: 326
Joined: Jun 21, 2012 12:48 AM
Location: Issaquah WA

Re: M5 Running Issues

Post by Preyupy »

That is definitely something sticking in the throttle linkage. If you are able to push it closed and bring the idle speed down. Now you just need to find where it is sticking. It looked to me like the throttle cable was tight before you pushed on the linkage it is quite possible you have a bad cable. Try disconnecting the 2 cables ( the other one is from the cruise control servo) and try gently opening the throttle about 20% and slowly close it. Do you feel any drag as it closes? Does it close all the way every time? If you close the throttle gently and then push on the linkage like you did in the video does it move? Try it with the engine off AND running it will give you an idea if vacuum is causing a bind in the throttle shafts/plates.

Also move the throttle cable by hand with it disconnected and see if there are any spots where it gets harder to move.
MattyCV
Posts: 63
Joined: Jul 21, 2017 11:54 AM
Location: Seattle

Re: M5 Running Issues

Post by MattyCV »

I will take a look at this today. I suspect it has something to do with the play/slop in the throttle lever. I think the clicking noise was the pin sliding back into place. It has a lot of play and isn't tight anymore and might be causing binding issues.

I've ordered this kit from Moosehead to at least fix the slop. https://www.ecwid.com/store/mhe/#!/S14- ... ry=1401064

I also bought a new cable, as it's finally available from ECS and if I'm going to mess with the throttle linkage, I might as well replace that while I'm in there.

The problem is that this issue is so random, it's hard to spot. When I got back home, I turned the car off and even tried forcing it but it just refused. She only likes to cause issues when it's impossible to pull over, but luckily I caught it happening at a gas station.

I think I'll cancel my order on the TPS now that I know it's definitely not that... :oops:
MattyCV
Posts: 63
Joined: Jul 21, 2017 11:54 AM
Location: Seattle

Re: M5 Running Issues

Post by MattyCV »

Small update. I changed the throttle cable and it really didn’t make a difference with the issue I’m having. Throttle response feels a tad better but it still feels laggy at the top end. It’s literally like it’s half throttle. I know it’s running at full throttle because when I open the hood and look at the linkage moving, it’s all the way open.

I also opened the hood and revved it a bit and the revs were coming down slow even though I could see the linkage was back down at normal idle level.

TPS still a possibility?
Randomg
Posts: 480
Joined: Jul 12, 2007 3:12 PM
Location: Seattle

Re: M5 Running Issues

Post by Randomg »

My throttle cable, where it connects to the bracket that is bolted to the throttles, is broken. It has been since 04 when I bought the car. One time when putting things back together, the broken plastic piece wasn't sitting right and the cable wasn't letting the throttles close all the way. If your cable is broken there, make sure it's not tight because it's been pulled out of place and isn't where it's supposed to be. The throttle cable should not be tight when the throttles are closed, there needs to be slack so that the throttle stoppers are what is stopping the springs.

Both of your symptoms, poor acceleration and slow return to idle, are explained by a bad tps. But the tps has two switches, one for wot and one for idle, usually only one fails first and the owner replaces it before the other one does too... Is this problem intermittent? Only when warm? Did you check the tps connector like I mentioned in my last post? There's a metal clip that should be there, sometimes the connector breaks where the plastic that actually does the holding in place is and the metal clip isn't doing anything anymore. A loose connector seems more likely to me than a tps that has failed both the idle and wot functions. I think the center pin of that connector is what makes both switches function, maybe take a look at that female center connector piece and see if it looks tight and if not carefully bend it so that makes sure to make a connection with the tps pin. I say carefully, because I wasn't careful once and had to replace the whole connector, not a fun job.

Probably should have suggested this earlier...
MattyCV
Posts: 63
Joined: Jul 21, 2017 11:54 AM
Location: Seattle

Re: M5 Running Issues

Post by MattyCV »

So...big update. And it’s not a good one. :cry:

Car was on a flatbed tonight. I checked the TPS clip and the throttle cable and everything seemed good. The metal clip clicked the connector into the TPS fine. I don’t think the issue is cold or warm related; and it was intermittent until it turned into something else completely. Nothing on the cable or bracket is broken - it’s a brand new cable, too.

It’s been consistently not going WOT even when I’m fully on the gas and intermittently sticking - I knew that. However. On the highway it would not get up to speed. I was in 3rd gear at 50mph and flooring it and it wouldn’t go more than a few MPH. I had to baby it to get it up to the speed limit of 70. Keep in mind, in 4th gear from 60-70, this car will hit triple digits very quickly, and it didn’t even want to go up to the speed limit.

It felt like it was bogging hard. When I pulled off the highway it almost killed itself when I was pulling away in first but I babied it up to the speed limit. It seemed to stumble a lot, like a misfire - but when it was idling, it sounded fine and was staying consistent. When I revved it in a parking lot, the revs were climbing very slowly but I could see the linkage fully opening at max gas. It got progressively worse as time went on. It went from being able to baby it to being undriveable and not accepting any gas even with riding the clutch and clutch popping it. When it came to a stop, my oil pressure light came on and I turned my car off immediately (I was on a small uphill incline, very minimal though). Oil at correct level, none under car. So now I might be dealing with a bad oil pump, but I don’t know if the issues are related.

I’ve never experienced anything like this before. My dad thought it could be the ICV, as mentioned, but it could idle okay and stay consistent. He also suggested the AFM but if that was disconnected, the car would die on idle which it doesn’t. The revs just don’t want to go up with the throttle input. I connected and disconnected the TPS, too - no difference at all. Tried driving it with and without and it made zero difference too.

I can’t express how grateful I am for all the help I’ve been getting. The car will not be turned on until I can figure this out. Thank you for giving me ideas to try out and test for, it’s really helping this process! And from what everyone has said and what I’ve read and the shops I’ve called - the TPS sounds like it could be doing this. Why it’d go from okay to not possible to drive with in a span of 10 minutes is beyond me, but if it’s been failing this whole time then it’s possible it finally went.
milarsky
Posts: 515
Joined: Jan 26, 2013 11:19 AM
Location: NYC

Re: M5 Running Issues

Post by milarsky »

Sorry to hear about your troubles. If unplugging and plugging in the TPS provides no change then that might be even more evidence that the TPS is completely dead. Can the experts chime in on this? I carry an extra in my trunk along with other ignition parts. It takes all of two minutes to swap out. I think it is around $50.
MattyCV
Posts: 63
Joined: Jul 21, 2017 11:54 AM
Location: Seattle

Re: M5 Running Issues

Post by MattyCV »

Yeah, I assume it's not working anymore since there isn't a change in RPM. I have the part coming next week so I will update once that comes in and I get a chance to put the new one on.

Sadly, it was not $50. A genuine BMW one costs a couple hundred right now, so it'd be difficult to carry an extra around :cry:
milarsky
Posts: 515
Joined: Jan 26, 2013 11:19 AM
Location: NYC

Re: M5 Running Issues

Post by milarsky »

No need to buy a BMW stamped TPS. Bosch part is perfect.
austin8753
Posts: 1444
Joined: May 16, 2010 1:37 AM
Location: Portland, Oregon, USA

Re: M5 Running Issues

Post by austin8753 »

Bought a new Bosch throttle switch, for my M5, last summer. They are now NLA, from my parts warehouse. I remember paying less than $100, list is $380. I'm sure you'll be able to find one out there.

13 62 1 273 277
0 280 120 301

AB
MattyCV
Posts: 63
Joined: Jul 21, 2017 11:54 AM
Location: Seattle

Re: M5 Running Issues

Post by MattyCV »

Ugh - I wish I had realized that earlier. Found the 301 part on FCP for $80. The part is en route and can no longer be cancelled and will be here earlier than if I bought another one and I really just need to get the car on the road.

However - I will be buying another one as a spare, just in case, now that I was made aware of the lower cost part. I appreciate having that pointed out! Seems like a good part to have if I take it on a big road trip and it starts acting up.

Part should be here in a couple days. Will let everyone know if it fixes the issue. I'm currently restoring my intake parts (plenum, ITB's, etc.) and ordered all new boots and hoses because they are unknown to me. Slowly but surely baselining this car :D
MattyCV
Posts: 63
Joined: Jul 21, 2017 11:54 AM
Location: Seattle

Re: M5 Running Issues

Post by MattyCV »

Put everything back together tonight with a brand new TPS. Still runs the same. Engine is losing revs when I press the throttle. Does not want to accelerate. Revs up slow.

Only difference is that induction sound is MUCH louder. I know everything is sealed properly. I triple checked all connections and everything is plugged in and all hoses are tight and brand new. Cleaned the ICV until no more gunk came out. I know the flaps and linkage are fine - I saw them opening up when I had part of the ITB’s off. Nothing stopping them or making them stick. The idle is still fine. No indication of an issue until I step on the throttle and try to move.

I’m at a loss.
milarsky
Posts: 515
Joined: Jan 26, 2013 11:19 AM
Location: NYC

Re: M5 Running Issues

Post by milarsky »

Hmm. I am sure more experienced people will chime in. Have you tried another M5 ECU?
MattyCV
Posts: 63
Joined: Jul 21, 2017 11:54 AM
Location: Seattle

Re: M5 Running Issues

Post by MattyCV »

Mia went to a shop yesterday. Y'all would not believe what it ended up being.

I figured, they figured, and everyone else figured it was a sensor acting up somewhere. Nope! Turns out, my FPR was dumping 100% fuel at any speed, including idle. It's been getting progressively worse because the cats have been getting more and more clogged with gunk. Well, they chopped the cat off and what do they find? So much gunk and destroyed metal that it was impossible for any gas to get through.

That's why it'd idle normally but bog under any throttle. If ANYONE has a similar issue to mine, check out your cat and fuel system too. I thought it'd be as simple as a pump at the worst but never thought a catalytic converter could do that.

It got replaced with some custom piping and while I haven't driven it yet (going to pick it up in the next hour), they say it idles perfect and pulls extremely hard all the way to 7k. I'm very excited. Since all of you have been so helpful, I shall post a video on this thread soon with the car hopefully acting very nicely. :D
milarsky
Posts: 515
Joined: Jan 26, 2013 11:19 AM
Location: NYC

Re: M5 Running Issues

Post by milarsky »

This is wonderful news. Please let us know that you love the ride. Just wait until you experience a well-sorted M5!

best,
jm
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