Idling Too High

[jackc]

Last weekend, the idle on my 93 ETC went nuts - idling around 2500 to 3000 rpm - which made for an interesting ride home, to say the least.

When I got home, I checked the plunger on the ISC motor and it appeared to be fully extended. I used the OBD to cycle the plunger in and out - which it did. But it sounded crunchy going in and out. I then used the override to retract the plunger and unplugged the ISC. After that, I was getting a quasi-normal idle and was able to get the car in the garage.

Some history: When I first got the car a year and a half ago, I was having some intermittent problems with it idling too high. But never to this extent. I've also heard some ratcheting of the ISC on occasion. The problem went away on its own, and has not come back up until this past weekend.

Yesterday, I went ahead and bought a new ISC motor and put it in last night. I noted that the ISC appears to have been removed before, because the bottom nut was missing. Its also interesting to note that there were signs that the brakes had been overheated before I bought the car, which leads me to believe that the runaway idle has happened before.

With the new ISC installed, I started the car last night, and was getting a near-normal idle. I have not yet done the Idle-learn procedure, but am planning to tonight, then test-drive.

I also need to walk through the diagnosis tree for a fast idle, which I'm assuming is somewhere in the FSM. I want to be sure that there's not something else causing the ISC to extend.....

I looked at the throttle body last night. Although its a little dirty its not enough to cause any binding - so I'm ruling that out as part of the problem.

So - I guess my question is whether anyone else has had this problem before, and what did it take to fix it. Are there other things on the input-side of the equation I need to be looking at (like throttle position sensors, etc)?

[adallak]

Your problem was most likeley the ISC motor itself. Replace it with the new one, and adjust the plunger so that there would be a 0.030" gap between the plunger and the the throttle lever when the plunger is retracted. If you have a mechanical pensil with 0.7 mm (0.0275") lead, the latter may be used for gap afjustment. See the "tools" I used to adjust the plunger and TPS. You do not need to disturb TPS if the engine idles normally. After adjusting the ISC motor, cylcle the ignition key two times.

[jackc]

Thanks adallak.

I'll have to spend some more time on the plunger adjustment. Mine was set at about a quarter of an inch.

BTW - that copper disc is an interesting tool. Any idea where I could get one of those?