high idle rev

75

Asked by Oct 28, 2008 at 02:49 PM about the 1986 BMW 3 Series 325e

Question type: Maintenance & Repair

When i start the car, the idle rpm in park and/or neutral is high. sometimes it will go up to 2500rpm and idle, after a minute or so, it jumps down to 1000 and occilates between 1000 and 1500. other times it will occilate between 1300 and 2000. but sometimes i start it, and everything is working well. idles at a 600-650 range. anybody know what this problem can be?

10 Answers

265

It could be at least one of the following: -Faulty intake manifold gasket -Vacuum leak -Just the engine warming up -Throttle Positioning Sensor Could be something else too, but that's all I can think of.

4 out of 4 people think this is helpful.
75

well its not just the engine warming up, cuz after driving for a while, i get back in my driveway, put it in park, and it goes up again. i was thinking it was the throttle position sensor, but ill check the other 2 while im at it. thanks a lot bro

2 out of 2 people think this is helpful.
4,425

Also take a look at ur IAC( Idle Air Control valve) this could be dirty and need a good cleaning. Also check your air filter and clear ur throttle plate off really good. This will help maintain the idle better. Even try to seafoam the intake of the car to clean the intake valve off for better air flow. Hope this helps.

2 out of 2 people think this is helpful.
55

i second this. most likely its the ICV (not IAC, sorry). take it apart and use wd40 to clean it out and reinstall. try to memorize positioning of the idle set screw (huge flathead screw) so the idle will be close to normal. if not wait till the motor is warm before adjusting this screw to tweak your idle. DO NOT use this screw to fix the current issue without cleaning it first. you will more than likely add more problems to the mix. worse case go to www.r3vlimited.com and use the search feature to research more options.

3 out of 3 people think this is helpful.
75

im gonna be honest with you guys, and go ahead and say that yes, im a noob when it comes to cars. i wanted to know where the ICV is located? i searched for pics and everything on google, but seems to be nothing really on its exact location under the hood. Any answers r appreciated ;)

5 out of 5 people think this is helpful.
95

In addition to everything listed above, i'd also check the coolant temp sensor. If it's faulty or out of calibration, it can cause the ECU to screw up idle enrichment and all sorts of stuff.

4 out of 4 people think this is helpful.
95

IIRC, the coolant temp sensor for the '90 M3 I have was about $17 at Autozone. I'd replace it anyways if you aren't certain it's been replaced recently.

2 out of 2 people think this is helpful.
35

I agree with the coolant temp sensor being the problem being the problem, happened to me not even 2 weeks ago, took me 20 minutes to change it and to be back on the road. The best way to check what the exact problem is to check the error code. Put your key into the ignition but not starting the car, only until the accessories come on and its starts to ding inside the car. Then press down and release the gas pedal 5 times and then let off the gas. The check engine light will then blink you the error code, pausing about 1 second in between numbers. It will be a four digit code and if it is the coolant temp sensor it should be 1-2-2-3. if it gives you something else just search for what it means online...hope that helps and keep us posted

2 out of 2 people think this is helpful.
95

It might not even show the code. The sensor in the M3 was far enough out of whack that it wasn't providing the correct resistance, but it still worked, kinda. I'd replace it regardless unless you know it's been done recently, if it hasn't gone now then it will go at some point.

1 out of 1 people think this is helpful.
45

Mine is doing the same thing. And I took the throttle body hose off just to see if it had cracks, and doing so, the IAC is attached to it and just reinstalled and the problem had stopped. Then when I drove about 2 miles it started again, so I'm going to get some throttle body cleaner and just clean all parts and see what happens tomorrow.

2 out of 2 people think this is helpful.

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