possessed idle
 

Car: 93 touring, 76k, dp, cb, grounding kit

So my idle has always been between 1200 and 1300, usually steady but every once in a while it would bounce a bit which could be fixed by flicking the parking lights on. In an attempt to fix the high idle I set to adjusting the TPS today. Warmed her up and went to work. The tps was a bit high in the narrow range with the throttle closed, so I set it within specs, reset the ecu, and turned her over. It was still 1200-1300 but at least no new problems. Then I started driving, about 2 blocks away from my house the idle started creeping up and started bouncing at about 2300 rpm. I thought that maybe it had cooled down too much when I set it the first time, so I hopped out and checked the tps again. It was high in the narrow range with the throttle closed. So I reset it again within specs for narrow and full range at closed and open throttle, reset the ecu, and fired her up. Bounced a 1300 for a bit then creeped up to 2300 again! It would actually push the car at 40 in 4th gear without any throttle. What have I done and what can I do to fix it?!

search for "hunting idle." There are many threads on this problem.

Areas to start:
1. TPS
2. ISC
3. Idle adjustment screw(s)
4. Throttle plates <---- I had a similar situation, one of my plates was stuck open and I had an idle at 3k.
5. Throttle cable

Is your double throttle eliminated or not?

Everything else is stock (double throttle, AWS, EGR, etc)

Make sure you TPS is on good you don't want it changing up on you like that. If you can close the idle adjustment screw all the way, as well as the air bleed screw, and your car still runs.....you have a leak somewhere in/past the throttle body.

How does one go about testing the ISC?

Just unplug it and see if anything changes in the idle.

I believe theres a resistance test in the FSM.

I guess I'll take a crack at it tomorrow if its not raining and I'll report back. . . thanks a lot guys

Here's an update, just in case someone is searching, has a similar problem, and would actually like an answer. Ok I pulled the elbow, throttle body, and extension manifold. The reason this took so long is that I decided to delete the double throttle butterflies, the AWS, disable the fast idle cam, and reroute the coolant so I had to wait for block off plates, etc. So I go to drop the extension manifold back in. . .and I see it. . .nothing. . .I didn't notice it when I pulled the manifold but there was no gasket between the extension manifold and the LIM! Having never pulled the extension manifold before, I kinda wonder who the culprit was . . . So this is mostly likely why I couldn't get the idle down. The gasket came in today, so I'll be putting her back together, I'll let you know if that cures it. Thanks for the help guys.

Update with slight changes in the problem symptoms. Ok everything is back together with the the fresh ex mani gasket. So no more AWS, DT, fast idle cam (fixed out of the way). TPS is in the proper range. I cleaned out the ISC (which was filthy) with intake cleaner and relubed with WD-40. Now the idle hunt is very specific. A lot of the time everything is fine (no surging etc). When it does happen it happens like this. I'm deceling, put the clutch in (runs down fine to idle speed so I don't think its the dashpot or the clutch switch), once it reaches the set idle speed it will bounce up 200 rpm or so a couple of times until I get to a complete stop. It basically stops surging every time the absolute second I come to a stop. I thought it was the brake booster check valve due to the association with braking but the valve is good and has had the relocation to the driver's side. The final weird thing is that this will absolutely never happen if I flick the parking lights on. Turning the lights on will actually stop the surging mid surge if I turn them on. This screams grounding issue to me, but I regrounded the car with 8 gauge cable (under intake to UIM to firewall and engine, battery to under diagnosis box to engine). Any other thoughts on what this could be? I'll take any suggestions. . . .P7k

its the idle screws next to the throttle body, just turn em a bit, and mess w/ em, u'll eventually get em in the correct spot.. i had the same problem, fixed it. 750 is the correct idle after warm-up, and dont be alarmed when the RPM rev to 3k when u first start the car, USDM cars do that, its an auto-warm sensor.. to warm the engine up faster.

I think that the air bleed and air adjustment screw are good to go since the idle is set to 800 and is rock solid (when its not having the surge issue). Also I removed all of the warm up stuff (AWS gone and no fast idle cam).

i have the same problem too but mine still idling high and bouncing but when light turn on, it stop. i've heard it might be due to bad ground connection. still trying to fix mine.

Why are you idling at 1200 with a stock motor?

As per my last post, I'm not idling high anymore. I've got it set to 800, but it still does the surging thing. I believe I have an idea though. Since the lights fixed the issue I decided to see what other loads fixed it. Turns out that if the rear defrost is on or the blower is set to setting 3 or 4 everything is perfect. This (to me) points to the electrical load system since its activated during 4 conditions (blower on 3 or 4, rear defrost on, lights on, or high water temp) to bump up the rpm via a signal to the ecu. Anybody have any experience/issues with this control system? I can't for the life of me find out where the thing physically is using the FSM. Ideas? maybe a bad ecu ground? maybe a bad EL unit? thoughts? humorous anecdotes?