e28 and e30 problems...grr.

E28 technical advice asked and given! Troubleshooting, modifications and more.
Post Reply
Beemernut
Posts: 173
Joined: Jun 22, 2017 10:36 PM
Location: Harrisonburg, VA

e28 and e30 problems...grr.

Post by Beemernut »

Hey all.

My only drivers currently are an 87 325i sedan and an 88 535i that's quite dear to my heart.

Sometime after completing the single Walbro in-tank pump conversion in the 5, I noticed a slight stumble when letting the clutch out at idle. That's alright, methinks to myself, just give it a little gas and we're good! At this point I'm getting 9-10 mpg, so something clearly is wrong. Fast forward to several days later, and I can't accelerate past 5000 rpm (just hits a wall), and the idle seems to be unusually grouchy even by M1.0 m30 standards. Later that day, I'm on the way home from a friend's place, and I have this increasing feeling of lost power, to the point where I would probably lose a race to a Trabant. This past Saturday I fired the 5 up and discovered that if I snap the throttle quickly enough, I can get a fantastic backfire through the intake. It might be worth noting that for the past year or so, this car has had a hard start condition.

The e30, on the other hand, barely wants to idle at all when I start it, and I've found that the only way I can get it to run without several minutes of initial sputter and power loss is to start and immediately rev to about 2000 rpm, and hold it there until I'm out of the "blue zone." (Sorry, oil pressure!) After that, it runs like a happy little sewing machine until the next time I have to start the engine cold.

I have coolant temp sensors on the way, because I'm an idiot...after testing resistance they seem (?) to be fine, although I'll probably swap one out at least. They both have new intake boots, so that is not a source of vacuum leak for either car. I even checked for vacuum leaks with carb cleaner, and one would think carb cleaner would show up a vacuum leak that's making either of these cars behave this badly. These cars also both have relatively new o2 sensors, and in the 5 I've replaced all ignition bits besides the coil in the last 30k miles.

Any ideas? I feel like I've run out of wits for these cars and if I can't figure out what's going on I may have to take it to a mechanic, which would bring destruction upon my wallet and shame upon my father's house.

Thanks in advance...
Shawn D.
Beamter
Beamter
Posts: 21991
Joined: Feb 12, 2006 12:00 PM
Location: Alpharetta, GA
Contact:

Re: e28 and e30 problems...grr.

Post by Shawn D. »

Have you checked the fuel pressure and condition of the spark plugs? Sounds like a failed FPR.
tn535i
Posts: 5585
Joined: Jul 14, 2006 1:30 PM
Location: Middle Tennessee

Re: e28 and e30 problems...grr.

Post by tn535i »

The e30 sounds like it's acting the opposite of a bad CTS or connection. The blue Bosch CTS which has better tolerance is the way to go. Usually they start fine and run worse as it warms so to test this thought just unplug it when cold and see if it starts and runs better until it starts to warms up. But could also be an problem with the idle control circuit. I believe an 87 should have the same 3 wire idle control as the 535. You need to study up on this control circuit.

IDK on the 5, anything from a FPR to an AFM or the idle control circuit or combination sounds like it's the problem. The computer goes open loop above certain engine speeds and if it has trouble revving to high rpm then fuel delivery or the AFM. I'm guessing the idle issues are the idle control loop and it's been discussed many times and easy to diagnose. Start by unplugging the TPS once it's warmed up and see what happens to the idle.

You say both cars have relatively new O2. Well that is your best initial diagnostic. Piggyback a meter on that output and see if rich or lean under these situations and it will give the best clues. I like an old analog meter with a needle on the 1 volt scale which gives you lean to rich meter. If under acceleration that needle isn't going to the right you have fuel delivery issues but anytime speed is steady it should be going back and forth across the middle. If always < 0.2v it is running lean but if >0.7 rich and it sounds like your 5 is running way to rich.

The O2 can also be bad or wet or grounded and make the DME think it needs to correct so another easy diagnostic is to simply unplug it and force the computer to run open loop without O2 feedback. When you've done this you can still watch the O2 output on a meter to see what's happening if it (O2 signal) is good.

When was the last time both these cars had a valve adjust? A dose of injector cleaner and maybe a hot soak? Air and fuel filters? Plugs and distributor cap & rotor? All 15-30k range service items.
Beemernut
Posts: 173
Joined: Jun 22, 2017 10:36 PM
Location: Harrisonburg, VA

Re: e28 and e30 problems...grr.

Post by Beemernut »

Shawn, I'm not sure if you're referring to the e28 or e30. I've recently swapped out the e28's FPR from a newer cheap parts store unit to a Pierburg, and it didn't help. I kept the "OEDirect" or whatever rando brand the old FPR is so I may swap it out to the e30 just for kicks. Spark plug looked perfect in the e28, in the e30 it looked okay but a bit more carboned-up.

TN, in line with what you said, I swapped the CTS on the e30 last night and after running beautifully at idle for about 1 minute, it shattered my hopes and dreams and nearly stalled on the way to the gas station. After filling up, I had to crank for a solid two minutes with partial throttle before it could be convinced to rev up to 2krpm. Interestingly enough, as far as CTS test is concerned, yesterday it wouldn't even try to start with the CTS unplugged.

A friend of mine suggested that the ICV could be sticking. I pulled the ICV and cleaned it with carb cleaner awhile back, but obviously this doesn't fix circuitry problems with the ICV. I need to figure out where my Bentley is...

5: I've calibrated the AFM within the last several years, and moved the wiper arm to a clean track fwiw. I might check on it again though.

I've had issues in the past with O2 sensor wiring coming apart due to my inexperience/sloppiness and it resulted in similar issues. If it will revert to some default fuel map unplugged, that should make for an easy step in diagnosis.

Valve adjust on the e30 happened this spring I think but I may have put 15k on it since then. E28 got a valve adjust since I moved to VA I think? that would be within a year and a half. Injector cleaner probably worth a try. Air filter is a cone filter that I could probably clean some crud out of. Ignition stuff on e28 was done within 30k miles, ignition stuff on e30 was inspected on the e30 and seemed to be fairly recent.

E30 has had a fuel filter changed in the last year I think. E28 might need another one due to pump failure possibly. I have one on hand.

Probably going to swap fuel/main relays on the e30 as I've heard of them having a failure mode when cold.
Beemernut
Posts: 173
Joined: Jun 22, 2017 10:36 PM
Location: Harrisonburg, VA

Re: e28 and e30 problems...grr.

Post by Beemernut »

Update on the e30: I've swapped main/fuel relays to no avail, and changed the fpr. It seemed like I got a tiny bit of difference when I jiggled around the wiring going to the ICV, so I hit the connection with electronics cleaner, waited for the engine to get cold again, also didn't make a difference in the end. I'm absolutely stupid when it comes to circuitry, so I'm not sure how to test the ICV circuit tbh.

It seems worth noting that I could sometimes manually get it to idle better by very carefully nudging open the throttle and holding it open just slightly past the first "click" of the TPS. If the following doesn't help anything, I may go with the bandaid fix of adjusting the throttle cable to make it idle at 1200 rpm or so.

Battery has been disconnected all night, and o2 sensor is unplugged, curious to see what readings will be and whether it runs any differently without the o2.
Beemernut
Posts: 173
Joined: Jun 22, 2017 10:36 PM
Location: Harrisonburg, VA

Re: e28 and e30 problems...grr.

Post by Beemernut »

Update 2: fired up the e30 at lunch. Ran fine for about 10 seconds, ran horribly for about 30 seconds, then magically smoothed out with no coercion, and I couldn't get it to act up again (but after a couple minutes the engine was warm).

O2 sensor, while unplugged, read about .17 volts shortly thereafter and rose and leveled out to .39-.41 over about one minute.

I know better at this point than to assume that it's "better" now but at 55 degrees it didn't run horribly near as long as it likes to.
Beemernut
Posts: 173
Joined: Jun 22, 2017 10:36 PM
Location: Harrisonburg, VA

Re: e28 and e30 problems...grr.

Post by Beemernut »

Update 3 (I'm sorry if these are getting annoying): O2 on e30 is still unhooked. Now the idle hunts a bit as if it has a vacuum leak (EXTREMELY likely) but now I can't get it to misbehave when starting cold. These symptoms seemed to worsen in cold/wet weather, but now it's been starting just fine at 48f. Even seems quieter through the whole powerband.

So either the problem lies in the pretty new o2 sensor itself, or reverting to the base fuelmaps has made it disappear.

f o r n o w .
tn535i
Posts: 5585
Joined: Jul 14, 2006 1:30 PM
Location: Middle Tennessee

Re: e28 and e30 problems...grr.

Post by tn535i »

When a motor gets out of whack in more than a couple areas it can be a problem bringing it back. Mixture effects ability for idle control to work properly and if idle control isn't working well then you have two issues impacting idle.

Do try the test where you unplug the TPS once the engine is warm, if the idle control and ICV is working properly the engine should speed up a little, maybe a couple hundred rpm, but it should not slow down and struggle. If it does the base throttle position is too far closed or the T/B is just very dirty. If you reset the position or clean it you may have to readjust the TPS.

If your O2 sensor voltages are correct, then it sounds like the AFM is allowing the car to run slightly lean with O2 unplugged. However, that could also be a vacuum leak or boot from AFM to T/B and first hunt those down. It's better if with the O2 unplugged is runs slightly rich. You can tweak that adjusting the AFM spring no more than one notch at a time but only if you are sure you've eliminated leaks.

Have you done simple test for vacuum leaks... raise the dipstick when it's warm and idling, it should stumble a little, then remove the oil fill cap and it should stumble a lot maybe even stall. If not... you have vacuum leaks.
Beemernut
Posts: 173
Joined: Jun 22, 2017 10:36 PM
Location: Harrisonburg, VA

Re: e28 and e30 problems...grr.

Post by Beemernut »

The e30 seems to be having the problem less, but it still happens and seems to be most frequently an issue when it's cold and wet outside.

I've sprayed water from a bottle around the various intake components to see if I can force any of the symptoms, but no luck there.

I did the dipstick test, and it stumbled a bit before evening out to a chunkier idle; removing the oil cap made it run really badly. So I would say any vacuum leaks are probably mild enough to not be causing this particular problem. HOWEVER, I'm willing to consider that there could be certain circumstances causing a vacuum leak to appear.

Unplugging the TPS once warm did what you described, it raised the idle by about 100 rpm, which in this case meant going from 600 to 700 rpm.

Maybe the cold start valve is leaking? If this car has one? I've read so many threads that describe basically identical problems and seen everything from coil to CSV to even a flaky crank position sensor.

I want to reiterate what happens when this problem rears its head. I'll start the car, and after a few seconds the idle bogs down to a couple hundred rpm, and barely wants to run. If I don't rev it up soon enough, opening the throttle wants to make it stall, and getting the car to start and stay running again becomes increasingly difficult. Once I get it up to 2000 rpm or so, the idle eventually evens out and it purrs away...but at that point I keep holding the throttle until the temp needle leaves the blue zone.

Now this hasn't happened lately, but sometimes it takes a minute to exhibit the issue. By that point I'm sometimes rolling down the road, and the car will start bogging as if it's not getting fuel. But as long as the engine is hot, it runs like a champ.

Hopefully the weather gets cold/moist enough that I can perform some tests while the e30 is misbehaving.
JohnH
Posts: 693
Joined: Jan 24, 2007 9:55 AM
Location: Surrey,UK

Re: e28 and e30 problems...grr.

Post by JohnH »

Sounds like a misbehaving Coolant Temperature Sensor.

When you start the engine initially, it runs okay because the cold start injector is working. Meanwhile the ecu has leaned out the mixture because it thinks the engine is warm. The cold start injector ceases operation and the engine stumbles. All this happens in the first few seconds.

Try disconnecting the WTS before you try starting from cold. Everything will be okay until the engine warms up and starts stumbling because its running to rich. When that happens jump the connector and everything should calm down.
Beemernut
Posts: 173
Joined: Jun 22, 2017 10:36 PM
Location: Harrisonburg, VA

Re: e28 and e30 problems...grr.

Post by Beemernut »

Thanks for the input John.

I was hopeful that it was the coolant temp sensor so I replaced that about a week ago to no avail.

I have the car scheduled for a smoke test tomorrow, I'm nearly guaranteed to have a vacuum leak somewhere due to the car's age; if so, hopefully fixing the vac leak will fix the problem?

I suppose I could be having issues with the wiring going to the coolant temp sensor. I'm not sure how to test that and electrical work is NOT my forte.

Edit: the coffee hasn't quite kicked in yet so I'm not sure what you mean by the WTS.

Also edit: this is an 87 325i. Does it have a cold start valve or was that exclusive to the Etas?
Beemernut
Posts: 173
Joined: Jun 22, 2017 10:36 PM
Location: Harrisonburg, VA

Re: e28 and e30 problems...grr.

Post by Beemernut »

Smoke test showed ZERO vacuum leaks which came as a huge surprise and kind of a disappointment to be honest.

Mechanic said I should do a valve adjustment; it's been probably about 15k since I did the last one, so I'll probably give it a shot...
Beemernut
Posts: 173
Joined: Jun 22, 2017 10:36 PM
Location: Harrisonburg, VA

Re: e28 and e30 problems...grr.

Post by Beemernut »

E28 & E30 UPDATE

E28: when I upgraded to the TRE Performance in-tank pump, I failed to replace the wimpy rubber coupling from the pump to the pickup tube. Naturally, a 1/2" crack opened up in it. I "fixed" it with a piece of 5/16 submersible fuel hose jammed inside a piece of 1/2" standard fuel hose...which I'm guessing could give me issues down the road, so I need to find a proper piece of 1/2" submersible. E28 now runs as well as it did before, quite happy about that because the...

E30 blew the brakeline that goes over top of the fuel tank as a friend was helping me bleed a new brake caliper :roll: Seems to be having its cold start issue less, but we've also had a bit of a warm period the last week or two down here.
tn535i
Posts: 5585
Joined: Jul 14, 2006 1:30 PM
Location: Middle Tennessee

Re: e28 and e30 problems...grr.

Post by tn535i »

Beemernut wrote: Sep 28, 2021 8:40 AM Unplugging the TPS once warm did what you described, it raised the idle by about 100 rpm, which in this case meant going from 600 to 700 rpm.

Maybe the cold start valve is leaking? If this car has one? I've read so many threads that describe basically identical problems and seen everything from coil to CSV to even a flaky crank position sensor.
When you unplug the TPS the ICV should go to a baseline position, and then idle speed would generally be a couple hundred rpm above 'normal idle'. It might be worth a try if you are comfortable with it to bump the ICV wide open and see where it idles warm with both TPS and ICV disconnected. You could remove the ICV and experiment with it and maybe a 9v battery will even work to extend and retract it. On the 3 pin the center is ground and the outside pins are extend and retract which is which you'll need to know. So for example if you bump the ICV wide open and the idle is still only 700 rpm or so it is unable to open wide enough to control idle properly, perhaps you have a very dirty or too tightly shut throttle butterfly. If the ICV were wide open and the engine warm I would expect idle to be 1200-1500 rpm. If not, there is not enough range to keep idle speed up when there is a cold start and it needs to be more open. Another thing just to check since issues seem intermittent are the bundle of ground wires near the head for all this stuff on the engine.

I don't think an M20 'i' has a CS Valve or Injector. If leaking it makes the car run rich but the computer can probably compensate for smaller leak.

Another thing I did not mention earlier is the bypass on the AFM which can be used to adjust mixture at idle speed. If too far one way or the other the computer cannot compensate. You want a known working O2 sensor in place and measure it while you make any adjustments, But you could try just turning it keeping track of which way you move it and see if it improves.
Post Reply