Idling issue

[FreedS4]

I've developed an idle issue over the course of the past week. On start up the car jumps up to 1250RPM or so, then drops back to 500RPM and sometimes acts like it is going to die, but then jumps right back to 750ishRPM. Then it idles relatively smoothly. When I'm driving it around and push in the clutch, the idle drops down again to 500RPM and then climbs back up to 750ishRPM. Also, the car seems a little jerky if I'm in gear and barely giving it any gas. Another point of note is that it seems to get better, meaning not as much of an RPM drop when I let off the gas in neutral to almost no drop at all, when the car warms up. Any ideas? Thanks in advance.

Chris

[jlevie]

That sounds like a sticky ICV, probably aggravated by intake leaks.

[FreedS4]

That sounds like a sticky ICV, probably aggravated by intake leaks.

What's the fix for a sticky ICV? I checked the resistance acrosst the terminal and the ICV itself tests good.

[jlevie]

Remove the ICV and use carb cleaner on it until the vane moves freely.

[FreedS4]

I'll give it a try, thanks.

Chris

[FreedS4]

On start up, it's acting like it wants to die even more now and hovers around 500RPM until it gets nice and warm. Ran a smoke test today, no leaks. ICV has been cleaned and appears to be working. Any other thoughts?

[jlevie]

With intake leaks ruled out now you have to consider other possibilities. A fuel system pressure check should be run and you need to check to see if the AFM vane is sticking. If the O2 sensor has 100k on it, replace it. Another possibility is a bad DME engine temp sensor. You also need to check (electrically) the operation and adjustment of the TPS.

[FreedS4]

With intake leaks ruled out now you have to consider other possibilities. A fuel system pressure check should be run and you need to check to see if the AFM vane is sticking. If the O2 sensor has 100k on it, replace it. Another possibility is a bad DME engine temp sensor. You also need to check (electrically) the operation and adjustment of the TPS.

Thanks Jim, I've got a lot of testing to do this weekend.

[FreedS4]

My TPS wasn't reading any ohms until it hit the idle stop and sometimes didn't register ohms at all. I've adjusted it so it's reading accurately now and my idle seems a litle more stable and doesn't want to cut out when I let off the gas abrutly. The RPMs also don't drop as far down as they used to when I let off the gas. The only thing I haven't checked is the cold start-up and it's tendency to almost die at first. I'll let her cool down fully and check it out, but all signs point to it being fix, or at least better. Thanks for all of the help.

[FreedS4]

My TPS wasn't reading any ohms until it hit the idle stop and sometimes didn't register ohms at all. I've adjusted it so it's reading accurately now and my idle seems a litle more stable and doesn't want to cut out when I let off the gas abrutly. The RPMs also don't drop as far down as they used to when I let off the gas. The only thing I haven't checked is the cold start-up and it's tendency to almost die at first. I'll let her cool down fully and check it out, but all signs point to it being fix, or at least better. Thanks for all of the help.

Just went and started her up and she's having the same issues as before on start up. Jumps up to 1000ish RPMs, then drops to 500ish RPMs and settles at around 600-650 RPMs. If you give it some gas and then let go, it drops to 500 RPMs or lower and almost dies. The idle seems a little more stable when she finally gets warm, but when cold, not so much.

[Philo]

Sounds a lot like a voltage regulator going bad. I would pull the regulator off of the alternator and check the bushings. Make sure they are long enough. It's a simple check that takes less than 5 min.

[FreedS4]

Sounds a lot like a voltage regulator going bad. I would pull the regulator off of the alternator and check the bushings. Make sure they are long enough. It's a simple check that takes less than 5 min.

Hmm...explain in further detail...

[Philo]

What further is there to explain? Your brushes are worn, making the alternator not generate enough current to provide the car. It dips, then levels out. Happened to my car one month ago. Just check the brushes.

[FreedS4]

What further is there to explain? Your brushes are worn, making the alternator not generate enough current to provide the car. It dips, then levels out. Happened to my car one month ago. Just check the brushes.

Can't say I've removed the regulators from an alternator before. I was looking for an explanation on how exactly one would go about doing what you recommended. Thanks for the help.

[Philo]

If you want to give yourself some room, you can remove the AFM and airbox from the bay. This is what i do because I like seeing what i'm doing. Then there are two phillips head screws on the backside of the alternator that hold in the voltage regulator. Unscrew those and it should come right out.

For pictures:

http://www.pelicanparts.com/bmw/techarticles/101-Projects-89-Alternator/101-Projects-89-Alternator.htm

the guy you want to remove.\/ Brushes.
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