Sort of low idle problem?

[Pocket Chant]

Okay, so here's the issue. It's been damn hot lately, so I've had the AC on pretty much constantly. The car starts up and runs smoothly, and idles at about 700RPM.

HOWEVER!

If I turn off the AC, the idle drops to about 400 and becomes very rough. I know that the compressor runs off the belt, and that is why the RPM changes, but I don't think the idle with it off should be so low. Thoughts?

[UserError]

Sounds like a bad idle module, since it idles normally with the AC on. If you have an older 325e, then the idle valve is adjustable, so you can turn the screw on it to set a higher idle speed with the AC off, and see how that goes. If it's an i motor, then you're stuck with replacing the idle valve, though the module is a lot more likely.

[jlevie]

The HVAC system provides a signal to the DME to increase idle speed when A/C is selected. In this case that increase is compensating for some other problems. The first actions should be to smoke test the intake and fix any leaks revealed, remove and clean the ICV with carb cleaner, replace the O2 sensor if it has 100k on it, check the idle switch in the TPS (with an ohmmeter), and adjust the valves.

[Pocket Chant]

Well, it seemed to miraculously resolve itself this morning. I hadn't checked it in a few days with the AC off, so it might've just been the conditions. *shrug*

Though my valves now tick when it's cold, so I guess that's my new project!