328 Fast Idle

At the first stop after a long freeway run, my '89 328 will often times idle between 1500-2000 rpm and continue to do so each time thereafter when the car idles. It is NOT the carpets (I've seen to that) and the throttle linkage has been thoroughly lubed. When it is not doing this, it idles perfectly at 1000 rpm. It runs perfectly. Any ideas?

Thanks for your help.

 

Mr. Crall:

Thanks for your response. Actually, the only thing that seems to be successful in having the idle return to normal is a quick blip of the throttle. Can you offer any suggestions based on that info?

Thanks again!

 

I'll check the throttle body as well as the slack in the throttle cable. Thanks to Brian and Iain.

 

I see the device (heating element under the coolant overflow) you are talking about but I do not see any wires going to it. How (and why) does electricity get there?

 

You're absolutely right-I can't see it but I can feel the electrical connection to this device. It seems to be intact and have a firm connection. What does this device do?

If my recent throttle body cleaning doesn't solve the problem (it was pretty grimey in there but I don't think it was so bad as to prevent the plate from fully closing), I'll further investigate this device. I gather, however, you feel that if a blip of the throttle returns the idle to normal, then this device probably isn't the culprit, correct?

 

My cold start seems to be normal - starts after a few cranks, idles for a moment or two at about 1500, then slowly comes down as the car warms up. I usually don't begin driving until the car is warm enough to idle at about 1000 or so. Then I drive very gently until the car is fully warm. I really don't think this device under the coolant tank is my problem. I'll report back after I've had a chance to see if cleaning the throttle body helped.

Any other conditions which might give the symptoms I've described in my original post?

Thanks very much.

 

Thanks very much - it does help. I actually did what you suggest when I was cleaning out the thottle body. It does appear the flapper plate fully closes whether snapped shut or closed slowly. As I mentioned in an earlier post, there was a fair amount of grime in the throttle body and I'm hopeful that cleaning will solve the problem. The throttle cable and linkage have all been thoroughly lubricated so I don't think that's the cause. It's odd in that while at a stop light when the car is idling too fast, I can even reach down and try to pull the accelerator pedal up with my hand and it won't move any further up yet if I slightly blip the pedal, the idle will return to a rock-steady 1000 rpm. I'm a little worried that the problem is more systemic with the fuel injection and may require a trip to the mechanic's. Anyway, as soon as I finished cleaning the throttle body it started, once again, p*ssing down rain here in San Francisco so I'll have to wait to see if my cleaning efforts have solved the problem. I'll certainly post again once the weather improves.

Again, thanks for your help.

 

That's it!! I'm moving.