Idle going up and down...

[ivopivo]

I have an 87 325e with about 201k on the clock... Purchased last night and just registered a few hours ago!

I searched a bit but usually found people with high idles, whereas the issue with mine is that it will sometimes, maybe 1/3 of the time the car's on, sit at normal idle 700-800RPM, and the other 2/3 it will simply go up and down, between ~700 and ~1200, as if someone was lightly pushing the gas. It never goes past 1200 or so and doesn't dip below 700 where it would seem like it'll die out.

Where could I start in fixing this?

Thanks in advance.

[Pennyw1se]

Check for vacuum leaks. Most of the time its one or more cracked vacuum hoses. Its very possible that your 20 year old car has never had these hoses replaced. It will take some time but you should be able to find it.

[jlevie]

Intake leaks, sticky ICM, bad ICM, or a combination of those.

[SpecM]

Check for vacuum leaks. .

I woud start with this, and a good cleaning of the ICV

[ivopivo]

Ok after much research (as much as I can do in 4-5 hours during work today) I've come to the conclusion that I have no clue wtf is going on haha.

According to the very thorough and informative writeup here... http://www.mesaperformance.com/faqs/idle.html

the ICV isn't working if the RPMs fluctuate 700-1200RPM, meaning it's simply wide open and isn't controlling anything. Either that or the ICM isn't telling it to open/close. Considering the fact that I'm right around 33% with each case (idle fine at 750ish, idle high at 1200ish and idle going up and down 750ish-1200ish), it would be easiest to suspect a vacuum leak somewhere, simply because I know the ICV is working and so is the ICM at least 2/3 of the time. I'm going to start with the propane torch test and if it doesn't work try smoke, hoping to find the culprit.

Now I'm simply confused about how all three instances above are so irregular, meaning either a leak is sometimes there and sometimes isn't (damn leaks) or that there might be a bad connection between ICV and ICM (or a bad ICM connection) so that the electrical components are going on/off at times...

I'm going to deal with this and my cooling troubles tonight so hopefully I'll be posting something positive in 3-4 hours.

[ivopivo]

BTW, what's a good temporary fix to a vacuum leak on a hose? Obviously if I find it I'll order new ones but will need to seal it with something temporarily just to see if that is in fact it.

Also, with the penny trick, which I might end up trying, where does the penny go, the hole at the end of the ICV or the one coming out of the side of it?

Thanks.