Idle Control Valve Replacement

[scottb]

I'm about to replace the idle control valve in my 84. It seems pretty straight-forward. Any hints, tricks, pitfalls, or landmines I should be looking for?

Thanks.

[jhugh]

It's totally basic. No worries. I did it to my '84 as well. I thought I was curing a wandering idle problem. But it got worse with the new valve, so I put the old one back! Now I'm theorizing that it has something to do with my light-clutch-with-stock-chip situation.

Cheers,

[scottb]

Thanks, Hugh. That's both encouraging and discouraging. Encouraging because it's an easy job. Discouraging because I'm trying to solve a fluctuating idle problem. Already did the O2 sensor, and if the ICV doesn't do the trick the next step will be to replace the Head Temp Sensor.

Thanks for the response. Cheers.

[jhugh]

There's also a throttle position sensor, which, some have theorized, can also cause the wander. I've never messed with that. Well, I suppose I would have by now, if my engine hadn't been apart for the past few months... At this point I'm just sort of blindly hoping that yanking the engine out, completely rebuilding it and putting it back in will solve that problem. We shall see.

good luck!

[smithH]

I am going down this road too, so please keep us posted on how you get on.

thanks.

[Tim Polzin]

Before replacing the ICV, have you checked the idle adjustment?

Some time ago, John Walker offered the following procedure for idle adjustment on the 3.2:

"use a round black relay, like the ones on the front fuse panel. pop the cover off and plug it in the test plug. push the top switch closed with your finger as you compare idle speed with and without pushing it. the speeds should be the same. adjust the throttle screw as necc. do it at normal operating temp."

This did the trick for me.

[scottb]

Tim: I have the classic symptom of the idle fluctuating between about 800 rpm and 1200 rpm on a very rhythmic basis -- up and down, up and down.... In reading the various threads, it seemed like the ICV was a "usual suspect." It's not a cheap part, so I'm hoping it will do the job.

[jwill911]

I'd try taking it (ICV) off and squirting it out with some carb. cleaner prior to replacing it. The head temperature sensor is a very likely suspect as mentioned. It is a pretty easy replacement Just a bit of a pain to get to. If it's not yet been replaced with the updated 2-wire one I'd do it anyway. With an ohmmeter you can tell if it's working or not. It's an inverse temp coefficient device, as the temp rises the resistance goes down. Cold should be > 2K ohms and at operating temperature ~180 degrees ~90 ohms.

[R22tech]

Fluctuating from 800 to 1200 huh.....Did you adjust the idle screw? If not, wait until your car is at normal oper. temp. and when it starts fluctuating, pop the deck lid and adjust the screw clockwise until it stops hunting. I'll try and post a picture of the screw in case you don't know where it is.

[R22tech]

lets see if this works:

[scottb]

R22: It's an intermittent problem. Sometimes it happens when the car is hot (while stopped in traffic), sometimes it happens at the beginning of the day when I pull out of the garage. VERY FRUSTRATING. Will the idle screw impact this situation?

Thanks for the help.

[R22tech]

Scott: Yes, it will impact the situation. Just get yourself a socket wrench with, I think, a 7mm socket and keep it close. When it starts to do it, pull over and start adjusting the screw clockwise a 1/4 turn at a time. If the idle settles down, it was probably mal-adjusted. If you get to the point where the screw won't turn anymore, then I'm wrong (wouldn't be the first time). Be sure to count how many rotations the screw turns in case I am wrong so you can adjust it back the way it was. I ran into this problem when I was attempting to RAISE my idle: I adjusted the screw counteclockwise a few turns which DID raise my idle satisfactorily. BUT....after a few drives, the idle started fluctuating on me as you describe yours doing. I adjusted it back and problem was solved. This fluctuation was INTERMITTENT, but seemed like it happend more when engine was warm, especially if I parked it, ran into the store for 10 minutes, and then restarted.

[Decolliber]

Last year a mechanic adjusted my idle using the voltage at the O2 sensor, made it too rich, and left the car with a fluctuating idle. Getting the idle properly adjusted by using an exhaust gas analyzer fixed the problem.

[Decolliber]

Oops. In my last post I meant to say mixture, not idle. Excessively rich mixture cause the fluctuating idle.

[jwill911]

Excessively rich mixture cause the fluctuating idle.

And that's why the 02 sensor can cause the problem. The DME controls the mixture based on feedback it gets from the 02 sensor, as well as input from other sensors.

Great book on "Bosch fuel injection and engine management system" by Robert Probst.

[scottb]

I replaced the DME relay and the O2 sensor. The ICV is "plan b".