1988 Carrera 3.2 with idle stabilizer valve humming after engine is off

[tshih]

Hi All,

Happy New Year,

a couple of times in the last 2 months I've found the battery discharged after a cold night and only about 3 days of not using the daily driver (1988 carrera). After charging the battery the car starts and runs fine. However one night when I was told one of my brake lights wasn't working I popped the engine lid to discover that there was a humming noise which I traced to the Idle stabilizer valve. The car has been parked for about 2 hours since I drove home and the ignition has been turned on only to check for brake light operation. Is it normal for the ISV to be humming any time the ignition is on (without engine running?).

[Laneco]

By ISV are you meaning the Idle Control Valve?

No, it should not be making that noise. You can clean them out. Just take it off, rattle it around a bit. The inside is metal, sort of a flap door, and you should hear it move easily. Clean the inside out until it moves freely and then reinstall.

That might clear that up as it sounds like it is still trying to move the flap door and it is sticking. Sorry I can't think of better terminology than "flap door" but that's about what it is - a heavy metal flap door.

angela

[steely]

Yes that is normal. With IGN on, the DME is energized. The DME provides +12 to the ICV and 2 rtn paths to ground. The paths are pulsed around 80 Hz, hence the hum. In fact, the hum with the ignition on is used as a quick test method to make sure the ICV is alive.

Of course, with ignition OFF, so should the ICV be off. So it sounds like you have a drain with the ignition off. Try to monitor the current draw at the battery - search here for a safe method and what the accepted mA range is (a bit for the clock, and that's about it).

good luck

[tshih]

Thanks all,

will search out current draw (of which I'm sure there are many sources due to the age and 173000 miles on the car).

[mray2686]

i had this same problem, ICV hummed after the car had been shut down. If I unplugged the DME relay, it would stop.

DME Relay replaced, problem solved.

[Laneco]

Tshih,

I mis-read your post. Thought you said it was humming 2 hours after shutdown (which is not normal). I missed the part where you had the key on, assumed you met 2 hours aftershut down with key off.... Key on - humming is normal.

My hooked on phonics order should be arriving any day now - LOL!

angela

[Tippy]

I figured you thought that. I misread too the first time.

[Lorenfb]

Read the title of the thread again:

"1988 Carrera 3.2 with idle stabilizer valve humming after engine is off"

Most assumed (and correctly) what the thread title said.

Need better thread starters!

[tshih]

Hey guys,

The ICV is humming after the engine and ignition is off. Like Mray2686 said the hum goes away when I disconnected the DME relay and replug it back. Will install a new relay and see if it helps.

[Spankster]

My ICV was humming after I turned off the ignition. I swapped out the DME relay and problem solved!

[gtc]

This has been happening to me. I'm glad to hear it might only be the DME relay!

[ischmitz]

From above it sounds like the DME is energized with the ignition off. Possible causes:

- Ignition switch bad (would see other items like oil pressure light remaining ON)
- DME relay 1st stage contact welded shut keeping power to the DME and thus making the ICV hum.

[Targa Me]

Bad DME relay.