Intermittent idle issue

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Glen
Posts: 25
Joined: Mon Sep 02, 2019 12:47 am
Location: Maine

Intermittent idle issue

Post by Glen »

Good morning everyone,
I was hoping to pick the collective brains of members to try and solve a new problem with my car.
I have a 1985 635csi that starts up nicely, drives to the highway well, and motors along at highways speeds just as expected....however, once I get off the highway, the idle starts wavering between 1500 rpm and stalling , which makes driving on secondary roads quite a frustrating chore at that point.

Any ideas what might be causing this?

Thank you all in advance for any insight. :)
plip1953
Posts: 400
Joined: Mon Aug 13, 2018 4:15 pm
Location: Leeds

Re: Intermittent idle issue

Post by plip1953 »

On the face of it I'd be thinking there might be a split/leaking hose that feeds the idle control valve. Failing that, maybe the control valve itself has developed a problem. Or the only other thing I can think of is that the main throttle butterfly isn't quite set right eg closing fractionally too much and relying on the idle control valve to have to work harder than it's designed to cope with.
Phil
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1988 Highline 635 CSi
Glen
Posts: 25
Joined: Mon Sep 02, 2019 12:47 am
Location: Maine

Re: Intermittent idle issue

Post by Glen »

Okay, as a guy who has ever only worked on busted up American cars, I had to do a YouTube search to even identify the part, but I found a video explaining the cleaning process, and it has worked.
Marginally...so I think a proper tune up is in order. :)
Thank you so very kindly.
plip1953
Posts: 400
Joined: Mon Aug 13, 2018 4:15 pm
Location: Leeds

Re: Intermittent idle issue

Post by plip1953 »

Glen wrote: Fri Jan 03, 2020 9:17 pm Okay, as a guy who has ever only worked on busted up American cars, I had to do a YouTube search to even identify the part, but I found a video explaining the cleaning process, and it has worked.
Marginally...so I think a proper tune up is in order. :)
Thank you so very kindly.
Did you clean the insides of the throttle body or the idle valve? There is no adjustment possible in terms of the idle valve, but the throttle body permits adjustment to the "closed" position of the butterfly ie very nearly, but not quite fully closed. It's also important to ensure that the throttle position sensor (black plastic unit with wires that's attached to throttle body) is correctly positioned (is has a small amount of rotational adjustment) to ensure that you can hear its internal micro switch clicking as soon as the throttle opens. Otherwise the ecu won't be able to tell if the idle control system needs to activate or deactivate.
Phil
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1988 Highline 635 CSi
Glen
Posts: 25
Joined: Mon Sep 02, 2019 12:47 am
Location: Maine

Re: Intermittent idle issue

Post by Glen »

I cleaned as much of the intake system as I could, with specific care paid to the ICV.
I will work on adjusting the other items today at work.
Thank you again, so very much :)
rhanley 635csi89
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Joined: Wed Sep 10, 2014 12:08 am
Location: Arden, NC 28704

Re: Intermittent idle issue

Post by rhanley 635csi89 »

Glen, pls post the link you found on YouTube. Thanks, Roger
89 635CSiA (11/88 build)
AlpineWeiss II (218)/Natur(0200)
87 L6 635CSI Sold
87 MB 560SL Sold
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