Z3 revs at idle (rpm up and down)

[Bmwcrocop]

My 1997 Z3 revs when I pull up to a light and sit idle. RPM goes up and then down. I have a K&N cone air filter with the associated sensor.

What would cause this?

Thank you

[Bmwcrocop]

Just a heads up I had a cracked loose rubber tube from the air intake to the engine. I’ll test it tomorrow and see if it fixes the issue.

[Randy Forbes]

Check the rubber boot between the air filter and throttle body. If it's the original, good chance there's a hole in it. If you've just installed the K&N* setup there's a good chance the movement put a hole in the boot.



* DO NOT OVER OIL THE K&N FILTER, it'll kill the MAF.

[Bmwcrocop]

I replaced the rubber air intake a few months ago. Today I looked and I have a cracked end on the Idle Control Valve Hose. I taped it up and zip tied it for a quick fix before I can order the new hose. I’ll report back if it fixes the problem tomorrow.

Thank you for the help and the info on oil w/ cone filter.

[sijray21]

does it only happen when the engine is cold(er)? if so it's likely the Vanos seals need to be replaced. that's currently happening to mine (has been like that for a few years now and i've been quite lazy to fix them).

[BladeRunner919]

... if so it's likely the Vanos seals need to be replaced..

Not on a 1.9!!

[sijray21]

oh, true - i forgot to check which version you had. your thought on a vacuum leak somewhere does sound like the right way to go first. any luck with that IACV fix?