My idle is bouncing!

[JamusMcFamus]

1986 535i - 170k

This just started about a week ago. Whenever I start the car after it's been turned off for a few minutes (or an hour or so), and I return to turn it on...the idle starts bouncing up and down from 500 to 1500rpm until i 1) turn the car off or 2) slip it in gear and start driving. Its really weird and is starting to piss me off! Thanks guys!

Jaime

[RonW]

Does it run well as long as you have your foot on the gas, even under light load? If so, I'd suspect the idle control valve. Try reseating its electrical connector first.

[JamusMcFamus]

Yes, it runs perfect while under load and all that. Only when I first start it up does it do this. I'll try the ICV procedure you told me.

[omagicbum]

I also exhibit similar problems, but I have problems with load. I have changed on the idle control valve 2 years ago. If I give it a lot of gas, than I can get the car moving. My car is an 1983 528e. What could be my problem? or do I have another icv problem?


[Edit by omagicbum on [TIME]1119841861[/TIME]]

[Guest]

I'd check the Throttle Position Switch "TPS" per the procedure described in the Bentley Manual.

Another thing to check is the inside of the Throttle Body "TB", make sure it's relatively clean and not fouled with oil blow by. The TB should allow a small amount of air to leak past the actual throttle plate. This in essence sets up the base idle, which should be at about 600 rpm. The Idle Control Valve "ICV" bypasses additional air as needed to maintain the RPM at a stable value. If the TPS isn't proerly adjusted the Motronic ECU doesn't realize you're at idle and will command other subsystems such as the ICV to do things they shouldn't be doing.

Another thing that can cause this sort of thing is an O2 sensor sending bogus info back to the Motronic ECU. A quick test would be to simply unplug the O2 sensor. If the idle surging stops when you unplug the O2 sensor, you're likely seeing the result of a defective O2 sensor coupled with the transport delay of the O2 sensor/Motronic ECU.

Rich

[a]

check ,IIRC, fuse #6, for loose contacts. It powers the ICV. AMHIK.

[slash02]

Before I realized that you cannot set Idle speed on the 528e, I adjusted the little screw on the TB that would appear to adjust idle speed. I had idle bounce all over the place.. luckily I marked it and set it back to where it was. Check that adjustment, also check the hoses goingt o your ICV.. if they are cracked and gross, you migth want to change them.

[RetiredDoc]

Have you done a google and roadfly and mye28 search about BMW and idle yet?

I did, and here is a good place to start.

http://www.mesaperformance.com/faqs/idle.html

[Guest]

[QUOTE="slash02"]Before I realized that you cannot set Idle speed on the 528e, I adjusted the little screw on the TB that would appear to adjust idle speed. I had idle bounce all over the place.. luckily I marked it and set it back to where it was. Check that adjustment, also check the hoses goingt o your ICV.. if they are cracked and gross, you migth want to change them.[/QUOTE]

slash,

that TB adjustment screw you tweaked that caused your bouncing idle problem sets the base idle, or in other words how much air is allowed to leak past the throttle plate. When you tweak this screw you now MUST readjust the TPS for proper operation.

Rich