98 Trooper high idle

[dtweed]

Sorry for the long post, but this one is frustrating…

Mid summer, a local shop replaced the IAC (Idle Air Control motor) to fix an occasional low idle / stall problem. As soon as we got it back, the idle started creeping up. First about 1100 RPM, then 1500, then 1800, then 2000, then 2200… We took it back into the shop and after much head-scratching, looking in manuals, they told us it was the battery – even though I tested it and it was fine (13.2V off, 14V running). I replaced it anyway. It was idling well for a while, then started going back up…

We took it in again, took them over a week to do basically nothing (other than hope and pray?), said they recharged the battery again and re-tensioned the air-mass sensor connector. Got it to idle. Its been working ok a little longer. Yesterday it was back up to 2200, so I started taking matters into my own hands.

I really suspect the IAC they put in is defective somehow, so I started messing with it – took it out, put extra Teflon tape around the body where the o-ring is. Viola! It idled perfect! I drove it around for a while, thought I had it. But alas – I turned off the key, restarted and it was back instantly to 2200. ARRRRRGGGGHHHH!

Anybody with ideas other than the IAC being bad before I go buy another one? Thanks for the help.

[rodeo02]

My guess would be a bad intake manifold gasket, or the idle up switch on the power steering pump is stuck.
G/luck
Joel

[dtweed]

Thanks - I don't think its intake manifold gasket because there is no hissing, and it does go back and idle right once in a while (after messing). I read elsewhere about the power steering pump sensor and was going to look into that tonight.

Any suggestions on how hard it is to get to that wiring? Am I looking for a connector ON the PS pump, or a quick connect elsewhere? And is this something I'd have to take the pump out for, or just remove something from the back of the pump? Can't find any good manual / docs for that one.

Thanks

[rodeo02]

If I remember correctly- it's a single grey wire, plugged into a sensor near the hi press line on the pump itself. You can just unplug the sensor. If the idle stays back to normal- that's what it was!
G/luck
Joel

[2eyefishclaw]

my 96 has been kicking my tail with simmiliar concern I have found that about every three to four weeks it would ide high well I found the throttle plate sticking not closing completly at times
cleaned t-body and all is well you. I have also seen problems with the P/S pressure switches on these next time you catch it acting up open the hood grab the throttle cable open it wide and fast then let it snap shut if it does not slow down cisconnect the P/S pressure switch your 6 cyl does not really need it all it does is raise the Idle a bit during hard turning

[dtweed]

definitely not the throttle body - even when I've gotten it to run ok, I can turn off the key, turn the engine back on WITHOUT touching the throttle at all, and the idle pops up instantly to 2k.

I'll try the P/S sensor wire once I can figure out how it disconnects. I think I found the wire, but cant quite tell which is which with the air compressor wires down there too.

[chaz3681]

I had a similar problem and replaced the egr valve, and it idles fine now.

[dtweed]

Originally Posted by chaz3681

I had a similar problem and replaced the egr valve, and it idles fine now.

Were you able to cycle the plunger by hand before replacing it? Most problems I've seen here in regard to the EGR is that it is gunked up by carbon and will not move. Mine has consistently worked fine in that regard (which is why I've been hesitant to replace it)

As an interesting side note to my ongoing problem, I've been resetting the ECU about once a week by disconnecting the negative cable for about 15 minutes, and the idle goes back down for a few days. Does any body know if there is a way to disconnect power to the ECU without having to clear everything else out?

[chaz3681]

Well I replaced the whole egr valve, but really all I needed was a new gasket for it and then I cleaned out the carbon the best I could. Another thing I had done was get my fuel injectors cleaned, but that was because it wouldnt stay running. Those are just my suggestions, if you wanna do some research on it.

[p-we]

to reset the computer there should be a plug to read codes.... three wire plug under the steering wheel two wires read codes and two clear codes....if you have obd2 then you have to either buy, or some parts stores will do it for you, or you can rent the code reader.....it is actually a handheld machine that will read codes or clears them......or i think there is a fuse for the ecm under the hood not to sure if it will clear the codes buti would think cutting power to the ecm would lose memory