ICV - nothing happens when I unplug it!

[monkeyodeath]

Been trying to diagnose a persistent low idle and cold start situation. My car doesn't idle faster during cold start, but hovers at a rough 600 rpm.

The ICV buzzes and is snapped shut when the ignition is on. I've cleaned it out and the door seems to work fine.

But when I disconnect the ICV plug, it has no affect on the car's idle at all.

Voltage to the ICV plug seems to be ok. Voltage between the center and side pins is about 6V. Resistance checks out ok.

What could be the problem here?

[barry]

Turn the ignition key to run position, but do not start the car, you should hear a buzzing sound from the ICV, and if you touch it a vibration, if not, the ICV is bad or there is no control current. Start the car run the system open loop by pulling the electrical cord from the ICV. RPM should climb to about 1500 to 2000 and then oscillate back and forth between 600 and 1500 rpm. If reconnecting the electrical connector has no effect on the RPM'S your ICM is probably at fault. Cut the motor. Pull the electrical connector from the ICV and connect an Ohmmeter across the terminals the reading should be about 9-10 ohms. If you get an open circuit it's time for a new ICV. If the resistance is much lower you've got a short and your ICM may be roached too, from the resultant excessive current draw.
Hope this helps

[nando]

what car do you have? M20B25s and '88 etas don't have an ICM.

[monkeyodeath]

Sorry, should have specified. It's a 90 325i, so M20B25. No ICM.

I hear a buzzing sound from the ICV, the resistance across the terminals is within spec, and it seems clean enough that the door inside moves about freely.

It's just that the ICV seems to have no affect on the idle. Nothing really does - cold engine, temp sensor disconnected, temp sensor shorted, O2 sensor disconnected...nothing. The only thing that affects the idle is disconnecting the TPS, which I'm sure is adjusted properly.

[jlevie]

Since the ICV buzzes with the ignition on, the ICV and it's control circuit is probably good. It not controlling idle then sounds like a bad idle switch in the TPS.

[monkeyodeath]

I've tested the TPS with the multimeter and tried with multiple ones, adjusting the throttle stop, etc. I've even tried just shorting the TPS connector to make the DME think that the throttle is at idle. Nothing helps.

[nando]

the only thing I can think of is the ICV is gummed up and not able to open past about 25% DC (~35% is about where warmup would be, ~50% is cranking DC, ~15% is closed)

[jlevie]

I've tested the TPS with the multimeter and tried with multiple ones, adjusting the throttle stop, etc. I've even tried just shorting the TPS connector to make the DME think that the throttle is at idle. Nothing helps.

Are you checking for the idle switch at the TPS, or at the DME connector. The latter is what counts. If you see the switch close there, I'd try a different DME and a different ICV.

[monkeyodeath]

No, didn't check the connection at the DME. The idle changes noticeably, though, when the TPS is closed v. open. It just seems that when the TPS is signaling idle position, somehow nothing's happening with the ICV. Unplugging the ICV causes no different in idle speed.

[nando]

if the idle changes with the TPS, then the ICV must be doing something.

I think, if you unplug the ICV, the solenoid will just stay in it's original location, which is why the idle doesn't change when you disconnect it while running.

you could take the ICV out and plug it in, then turn the ignition on and see if you can see the valve move.

[monkeyodeath]

if the idle changes with the TPS, then the ICV must be doing something.

What I don't understand is why unplugging the ICV doesn't do anything. Isn't vacuum pressure supposed to pull the shutter open and cause the idle to go up?

[nando]

no, I don't think so. it's not a flap door, it's basically a rod with a hole in it that moves side to side.

[monkeyodeath]

ah. i was under the impression that disconnecting the ICV was supposed to make the idle increase.

[jlevie]

ah. i was under the impression that disconnecting the ICV was supposed to make the idle increase.

Idle speed should increase when the ICV is disconnected. But other problems like intake leaks, sensor problems, or fuel system problems could affect that.

The first thing I'd do would be to have a smoke test run and fix any intake leaks. I'd also check rail fuel pressure and operation of the AFM, IAT, and ECT sensors.

[monkeyodeath]

I'll recheck those, but I ran a smoke test, and found nothing. ECT is a few months old and tests out fine. Fuel pressure is to spec, a little high when just cranking pump but within spec when engine is running. I have 2 AFM's - switching back and forth between them doesn't change anything. With current AFM, I moved the wiper to use unused resistance track. No dice.