2000 won't idle.

[Kelbro3]

I've got a 2000 S with 225k on it, 4.0 sohc 2wd, started getting a little rough idle, and then pretty quickly went to won't idle at all, above 2k rpms runs okay, doesn't miss a beat at highway speeds. Plugs and wires have less than 10k on them, and are gapped .54.
MAF tests okay, put on new Idle Control valve, TPS tests .95 volts to 4.58 volts, air cleaner is new, I don't hear any air leaks under the hood. It's throwing codes p1507-Idle underspeed error, P1130 O2 Sensor transition-fuel trim at its limit, p1150-Lack of 02 switches- bank 1 sensor 1 (ECM could not adjust fuel trim because of lean or rich condition) P0171-Fuel trim bank one condition,
and I don't have the code number on this one, but think it's a p0174- it says fuel trim bank two condition.
The fuel pressure test port goes to 58 PSI when the key is turned and slowly drops to 32 over 10 minutes.
I'm thinking It must be manifold gasket leaks or is it an O2 sensor? What about EGR? What do you experts think, where should I go next? I'm just a jackleg with a decent set of tools. Appreciate the help.

 

[96eb96]

How did you test the IAC? Did you clean it out? This sounds like a possible IAC issue.


Also, Check for any vac leaks (check the PCV system).

 

[Kelbro3]

I put on a new IAC, and I guess i should test it to be sure it's good, but nothing changed when I installed it. The PCV valve rattles as it should. I'll throw the gauge on the engine tomorrow and see what i'm getting in eng. vac. readings. Thanks

 

[2000StreetRod]

Gasket replacement time

EGR defects are usually detects by the PCM and reported as DTCs.

If your intake manifold gaskets have never been replaced then they're probably leaking. On an engine cold start the idle will flare and be unstable. The colder the weather, the worse the leak because the gaskets shrink. As the engine warms the gaskets expand and leak less or not at all. A set of upper and lower gaskets cost less than $30 but they are a pain to replace.

You may want to review my Lean condition procedure