whooping idle

[83justinMD]

My 83 533i has come along way. With the help of this forum I've fixed several of the problems but it will be an ongoing process. Thanks to all that have responded to my posts.

My newest concern happened this morning. When I first start my car in the morning it idles smooth and consistent at 800 -900 rpm, but after its warmed up and I stop at a light, it idles inconsistently at 1200 -1600 rpm, in a whooping manor and sometimes even drops down to 800rpm than back up to 1500 rpm.

I have a feeling that it's either the idle control valve or the oxygen sensor, or maybe even the AFM. All of which I would be replacing eventually anyway. Does anyone have any advice on a diagnostic approach to figure this out?

Also I figured via the Bently manual that 533's have a different idle control valve than later 535's, anybody know if they can be interchanged?

[Son of a]

Besides the idle issue, how does the car run otherwise? If the answer is some form of pretty damn good, then your problem is probably not in the engine bay. Now if it has some other running issue besides the idle, that is a different story, and you're going to have to address those problems as well.

You probably need an Idle Control Module (ICM). It is a little green box and it does (or tries to do) exactly what it says. After '85 BMW had the function of this little PITA integrated into the Motronic ecu. making the idle on the later cars much less finicky. Once you get another one, replacement is simple. And if the first one doesn't fix it, assume it is because the one you just got (even if new) is bad as well. The PO of my '83 533i had to try three before he solved the idle issue. Car has idled like a dream for the nearly 20k miles in my ownership.

[83justinMD]

The car is running very strong. Where did you purchase the ICM's from, Bavarian Auto or some other manufacture? And about how much did they cost?

[lanky_d]

I am having exactly the same problem on my 84 533i. It doesn't happen all the time though, and my idle will go as high as 2500. This only occurs after the car is at operating temp. If I'm driving around, the car seems to drive itself, kind of scary but i'm getting to the point where i'm ready for it.

Other than this happening inconsistently, it runs great! I have been trying to figure it out also, but since i can't easily replicate the issue, its been kind of hard to diagnose.

[nnarth212]

...my idle will go as high as 2500. This only occurs after the car is at operating temp. If I'm driving around, the car seems to drive itself, kind of scary ....

Completely unacceptable. If you want the car thinking for you-- lease a Prius, honda, lexus etc.



Fix that idle.

Vacuum leaks, bad ground, ICM, ICV.... all has been discussed in great detail.

You may want to find a local mye28 buddy and start swapping parts to isolate the issue.

[lanky_d]

Well, we finally have nice weather here and since I don't have a garage, that's key for auto work! I plan to poke and prod this Saturday and clean up as much as I can without spending any money and work up from there. I kinda wish it was happening all the time, that way i'd know I'd I'm actually accomplishing anything.

[a]

WAG, but it s quick ,cheap and easy. Clean up the contacts on fuse 6 and replace the fuse.

[Hans308GT4]

I've had the same thing on mine. Plus if I stepped on it, it would hold back a bit.

Changing the ignition leads solved the issue.

Hans

[Nebraska_e28]

One ez way to see if it's the ICM, is to whack the shit out of it! I was having the same problem & recall reading this somewhere. I whacked the hell out of that little green box with my hand & haven't had a problem since. **note: I had a spare on hand so if I broke it, I'd just swap it out.

[demetk]

It has to be your TPS. No way the idle will go that high if the ECU knew it was in idle mode.

[83justinMD]

Nebraska e28, thanks for such primitive advice, but it actually worked temporarily. I did purchase a replacement ICM but have not had the time to swap it out. TPS? Throttle positions sensor?, If that is what TPS stands for I have replaced both the position and reference sensor about 2K ago.

[Nebraska_e28]

Nebraska e28, thanks for such primitive advice, but it actually worked temporarily. I did purchase a replacement ICM but have not had the time to swap it out. TPS? Throttle positions sensor?, If that is what TPS stands for I have replaced both the position and reference sensor about 2K ago.

You're welcome, sometimes primitive can be effective. I can't really see a bad TPS causing your idle condition. From what I recall it's just an on/off switch for manual cars, & 5v variable voltage for automatic EH-tranny models. It's been a while since I've dealt with that though, so I could be off.

[demetk]

Nebraska e28, thanks for such primitive advice, but it actually worked temporarily. I did purchase a replacement ICM but have not had the time to swap it out. TPS? Throttle positions sensor?, If that is what TPS stands for I have replaced both the position and reference sensor about 2K ago.

TPS=Throttle position sensor. It's up by the throttle. Simple test is to disconnect it while idling. If no change in idle then you have a problem.

[DJM1986-5]

Agree with Nebraska E28.

#1 ICM
#2 IASV

Not the TPS - simply a switch on manuals.

Eliminate these variables - for $10 worth of vacuum line, replace it all at one time and every 50k miles. Also ensure no leaks from intake plenum, especially in the folds of the accordion. Lastly, in the same weekend, replace all fuel lines in the engine bay - especially the main inbound to the fuel rail and the 8 inch piece from the rail to the CSV. NOW you are ready to diagnose idle problems....
'nuff said

[wkohler]

Vacuum leak won't cause it to idle that high. Definitely the module, or the valve - and if you take everything apart to get to the valve, replace all the vacuum hoses (intake boot from AFM to throttle body, the vent hose - ONLY WITH NEW OE BMW HOSE - and the hose to the ICV).

[83justinMD]

Thanks for all the advice. After replacing the ICM, adjusting the TPS and replacing the vacuum lines, the problem actually got worse. I purchased a re-manufactured ICM for $25 on ebay which I used as the replacement, but it didn't fix the problem, so I switched back to me original ICM and the problem seems to be fixed, at least temporarily. This leads me to believe that it was a simple vacuum leak at the ICV. Either way problem solved for now.

[Scottinva]

Intake manifold leak. Sucking in large amounts of unmetered air, similiar to vacuum leak but way way worse.