Colossus

When I start it cold the Jeep's idle falls down to ~100-200 RPM then shoots back up to normal idling just under 1k. It will do this until its warmed up.
Sometimes stalls in reverse if the engine is still cold, hasn't stalled in drive.
All of this goes away when its warmed up.

Cleaned IAC, no change. Replaced with junkyard IAC, no change. Could be they're both bad.
Properly adjusted TPS.
No vacuum leaks.

Ideas?

ajpulley

Have you cleaned all your grounds? What else have you checked as part of your troubleshooting process... i.e. voltages, vacuums, continuities, etc.? It's apparent that the issue is most seemingly a thermal problem, or combination thereof.

cruiser54

Go to my website and do Tips 1,3,4, and 5 before doing anything else.

what method did you use to set the TPS?

Colossus

Cleaned up the grounds, doesn’t drop below ~400 RPMS now which is an improvement. Took cruiser’s advice and cleaned out all the connectors. Found a few corroded connections but nothing too bad. I did find a broken fuel pump ballast resistor
did a little reading and supposedly all it does it quiet the fuel pump but I’ll replace it just to be sure. I’ll let y’all know when I do.

Any other ideas what I should do if replacing the resistor doesn’t help?

cruiser54

Have you done tip 5 yet?
Ever cleaned the throttle body and IAC?

ajpulley

As in, pull the IAC out of its bore, and gently clean the pintle, and the opening inside the hole? Is it gummed up with carbon and gunk? Gently and lightly lubricate the o-ring on the IAC before re-inserting so as not to tear or stretch it. There is also a vertical hole that leads from a groove in the top of the TB that allowes filtered air to bypass the TB plate and enter the intake manifold via the IAC. Clean that hole too.

cruiser54

This:

http://cruiser54.com/?p=60

ajpulley

That.

Brilliant, just brilliant.

Colossus

I already tried gently cleaning the IAC, throttle body, and intake manifold. I don’t remember cleaning a small hole on the throttle body, I’ll have to go look for that.

Colossus

So I cleaned the throttle body again, making sure to clean out where the IAC sits really well. Also got a new throttle body gasket. I think there was a small vac leak there. Anyway I fired up the jeep and the strange idle drop seems to be gone, not 100% sure if it is though. I’ll check back in once I drive the jeep a little more. Thanks for the help.

cruiser54

Thanks for the report back.

ajpulley

You just have to be smarter than the material your working with.

Bugout4x4

I thought that for a long time until the material started proving me wrong in my assumptions.