High RPM rev when A/C on

[joonsup]

So my buddy picked up an 88 325i a couple weeks ago that had around 240k on the motor. He started to swap out a lot of the old bushings etc.. and is starting to look into the engine maintenance stuff.

One problem that we noticed after driving the car was that when he turns the a/c on and the fan is blowing, as soon as you tap on the gas the rpm would start to rise and it sounds like someone is stepping on the gas. It'll keep rising (i want to say up to around 4k?)

Then after a few seconds it'll drop back to normal idle. I don't recall the rpms jumping like that w/out the a/c on but I think it happened a couple times even when the a/c was not turned on. But having the a/c on can reproduce that rpm problem each time.

I'm trying to help him start in the right direction as far as what he should check first etc... so any information from you guys to help him out would be appreciated. Thanks

[jlevie]

That could be a sticky ICV, perhaps aggravated by intake leaks. Remove the ICV and clean it with carb cleaner until the van moves freely. A smoke test of the intake will reveal any and all intake leaks.

[smcdermott326]

is there a write-up for smoke testing the intake?

[joonsup]

ok i will tell him to check the ICV. Thank you. If anyone else has any suggestions, let me know thanks!

[jlevie]

is there a write-up for smoke testing the intake?

I don't know of a write up, but the process is pretty easy. Find a local shop that has the necessary equipment. Then take the car to that shop for the test.