525e Low Idle

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JayCee
Posts: 12
Joined: May 12, 2021 6:22 AM
Location: Melbourne, Australia

525e Low Idle

Post by JayCee »

Hi all,

Long time lurker, first time poster.

I have a euro-spec 86 525e auto with a low idle issue. I've done a search on here (plus Google) and read lots of articles on surging idles, bouncing idles, high idles but nothing similar to what i'm experiencing.

Symptoms: The car starts fine, cold or hot. Runs and drives well. Once warmed up the car idles at about 500rpm (indicated). It's not super smooth, but also not horrific, it doesn't feel like it's going to die.

Some articles state the M20B27 needs throttle plate adjustment, some don't, some say there's a mixture adjust screw, some say to leave this alone. I have cleaned out the intake and the ICV - and i'm confident that isn't at fault as the idle is stable, just low.

Is there a proper procedure to adjust the idle speed?

Thanks in advance.
Nothintoseeere
Posts: 57
Joined: Apr 23, 2021 5:27 PM
Location: U.k

Re: 525e Low Idle

Post by Nothintoseeere »

Is there a resistriction in any of the vacuum hoses?

Theres a whole bunch of stiff to check here.
https://www.msportster.co.uk/question/m ... bad%20idle.
It a case of working through it checking everything until the culprit is identified and fixed. The bentley manual will give spec for the electrical side of things.

It could be as simple as the throttle plate is too closed (not sure how this could happen) or something preventing the air flow meter flap from opening enough.

I take it the basics like the air filter is fresh.
JayCee
Posts: 12
Joined: May 12, 2021 6:22 AM
Location: Melbourne, Australia

Re: 525e Low Idle

Post by JayCee »

Yes air filter is clean.

Double-checked the ICV today, does the typical buzz with the ignition on, started the car and warmed it up then pulled the ICV plug and... nothing. No change, idled exactly the same, so maybe the ICV is at fault? I also noticed the TPS is fully rotated in one direction and also filthy, but i'm not sure how that would affect idle speed.
Ordnator
Posts: 550
Joined: Aug 31, 2015 7:34 PM
Location: Halifax NS

Re: 525e Low Idle

Post by Ordnator »

Is your TPS on the underside of the throttle housing?

My UK Euro 525e are and over time the TPS filled up with oil from the housing.

Currently replacing my housing and switch to try to resolve my issue.

Make sure your TPS is set up correctly as well and should be off at idle which kicks in the ICV. If it is on the partial setting then could well lock out the ICV and may be what you experienced when you un-plugged yours.

The Bentley Manual is quite good for setting up the throttle plate first then adjusting the TPS to the correctly adjusted plate.

Stay safe and best regards,

Mick
JohnH
Posts: 693
Joined: Jan 24, 2007 9:55 AM
Location: Surrey,UK

Re: 525e Low Idle

Post by JohnH »

Hi JayCee,

A couple of questions.
How long have you owned this car?
How much do you use it?

The other guys know how many beans make five, but a bit of background helps to solve some of these problems.

Regards
John.

Edit: 3rd question, idle speed in or out of gear?
JayCee
Posts: 12
Joined: May 12, 2021 6:22 AM
Location: Melbourne, Australia

Re: 525e Low Idle

Post by JayCee »

Ordnator wrote: May 16, 2021 7:51 AM Is your TPS on the underside of the throttle housing?

My UK Euro 525e are and over time the TPS filled up with oil from the housing.

Currently replacing my housing and switch to try to resolve my issue.

Make sure your TPS is set up correctly as well and should be off at idle which kicks in the ICV. If it is on the partial setting then could well lock out the ICV and may be what you experienced when you un-plugged yours.

The Bentley Manual is quite good for setting up the throttle plate first then adjusting the TPS to the correctly adjusted plate.

Stay safe and best regards,

Mick
Yes, frustratingly, so it seems like the only way to adjust it is to first remove the entire throttle body. And yes, judging from the filth I mine is also caked in oil from the intake.

Thanks for the suggestion, i'll see if i can remove it and clean it before trying to adjust it.
JohnH wrote: May 16, 2021 11:39 AM Hi JayCee,

A couple of questions.
How long have you owned this car?
How much do you use it?

The other guys know how many beans make five, but a bit of background helps to solve some of these problems.

Regards
John.

Edit: 3rd question, idle speed in or out of gear?
1) Not very long at all, a fortnight or so
2) Maybe once or twice a week at the moment, ideally i'd like to get it a point where it can take over daily drive duties
3) Both actually, changing gear doesn't really affect the idle speed
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