Idle problems

[DougG]

I recently replaced the water pump and the intake manifold gasket(IMG) on my 88 RRC. When I finished the IMG the truck started up and ran fine until I drove it. After I drove it for about 30 min, the idle seemed high. It didn't idle above 1000, but it idled steady at about 900 rpms. I replaced all the breather hoses when I did the IMG job and I cleaned the IAC(stepper motor). I can lower the idle by turning the black dial at the plenum end of the accelerator cable, but once I drive it again, the idle goes back up to 900rpms. If I close the butterfly valve by pushing on the lever on the plenum, I can lower the rpms, but it eventually goes up. Another symptom I get is when I depress the gas pedal very quickly. If I give the gas pedal a quick press, it sounds like the truck is getting a lot of air, but not enough gas, and feels like it might choke out. Once I let off the gas pedal it goes back to idling(high). I can rev the engine slowly without hesitation, but a quick press of the pedal, nothing. To me, the truck drives fine, but after driving for a while, the revs are high and it makes for harsher gear selection. My EFI light came on the other day, and I disconnected the battery and it hasn't come on since. Any ideas?


Also, unrelated to above, I have no reverse lights.
Thanks!

[OkieRover]

Is the air idler valve clean?

[DougG]

If you are talking about the thing that is at the back of the plenum with the four pin multiplug, yes I cleaned it. The manual calls it a Idle air control, or a stepper motor I think. But yes, I unscrewed it and sprayed carb cleaner in the hole, and I cleaned the tip of the Idle control valve.

[OkieRover]

Hmmmmm.
You sure you put the hoses all back where they came from?
Are you sure they were in the right place when you started?
And you've looked under the passenger seat and there are no codes on the display?

[DougG]

The breather hose that goes from the back of the plenum to the fuel pressure regulator was toast before I did the job, and I replaced it with new hose. I am positive that I put everything back where it belongs. I had everything labled and numbered. I took digital photos of everything before I started. As to whether or not things were in the right place before I started, I don't know. The truck drove well enough I guess. This is my first RRC. Could I have screwed up the butterfly setting when cleaning it? Are codes shown on a display under the passenger seat in an 88 RR?
I plan on following the workshop manual to do continuity tests of the IAC, MAF, and the throttle potentiometer.




What about the reverse lights?

[flunkster]

have you checked for vacuum leaks?

[DougG]

Everybody asks me that, but no one has explained where I should check. There are new breather and PCV hoses all around, and I used Hylomar blue sealent between the intake manifold and ram housing, and the ram housing and plenum chamber. Where else could I get a vacuum leak?

[OkieRover]

There is a vacuum dump on the brake pedal. Are those hoses replaced as well?

[DougG]

Are you talking about the hose from the brake servo to the ram housing? I did not replace that hose, but did a visual inspection, and it looked alright. The one thing that i'm leaning towards, is the TPS. I remember when I was doing the job, I had a real tough time disconnecting the multi-plug to that sensor. I really had to pull it hard before it came apart. I noticed the other day when I was looking at that plug that I can see bare wire where the wires go into the plug from the harness. I don't know if they are shorting out, or if I just compromised the connection and stripped some of the wire. Or, could this whole high idle thing be caused by the fact that I just refreshed the engine, and things are tighter and operating better? In that case, maybe all I need to do is a base idle adjustment. I talked to a guy at Atlantic British, and he suggested I do the base idle adjustment.

[Kevin88RRC]

Have you ran the test on the TPS? It's adjustable on the 88s.

[DougG]

Yeah, I plan on doing it tonight. I was going to do it the other day, then I saw where the plug is and it looked like a pain in the a** to get to. I'll just have to suck it up b/c it has to be done.

[DougG]

I did the continuity tests tonight as per the workshop manual. These are my findings:

Coolant temperature thermistor: 1100-1300 ohms at 104deg

Air bypass valve test #1: 54 ohms
Air bypass valve test #2: 54 ohms

Throttle Potentiometer test #1: 5000 ohms
Throttle Potentiometer test #2: .60 volts throttle closed, 4.6 volts throttle open.
If I push the throttle lever to close the throttle valve more, I get .37 volts.
The .60 volts with the throttle closed is high. What does that indicate?

MAF: .3-.6 volts.

So everything seems normal but the second part of the TPS test. So I either have a bad connection, or a bad TPS, correct? Thanks for putting up with me, and for your help.

[DougG]

New throttle position sensor cured the problem