Low idle problem, Please help.

Hello all, I am completely stumped with this one.
I have a 1994 l6 runs great, but has a low idle problem. It will not die but runs in the 450-600 range in gear when stopped. In park goes back up to a normal range. I have done all the checks of MAP, CTS, cleaned IAC and throttle body, new O2 sensor, plugs, wires, cap and rotor look new, and I'm sure others that I'm not thinking of right now. Everything checks out per specs according to the manual.
Anyone else have this problem and if so do you know of a fix. I don't really mind but it sounds like it is missing when it is running at idle in gear. Oh yeah and bad gas mileage, like 10MPH or less. I've spent hours researching and reading threads on this and other websites and can't find anything that matches.
Please help! gotta figure out something soon or sell the rig.
Thanks in advance
Kenneth

Fuel pressure?

Just a suggestion to check.

I wouldn't suspect that, runs normal through the range of the throttle, I did change the fuel filter though and it was in good shape. I'm thinking electronics at this point. I've never had a computer go bad but maybe?
Any one else with any ideas?

Good luck! I have a 90 RENIX and I have never been able to solve this one... everyone seems to have high idle issues....I WISH I did

Doesn't sound to me like you have a low idle problem at all. Mine runs 700 to 750 rpm in park at start up, about 700 rpm hot, and about 500 rpm in drive at idle. The spec is 750 rpm in park at idle warmed up.

It does sound like you have a gas problem, 4 am grmlins siphonig gas maybe, LOL, but seriously a number of things can affect gas mileage, but if the car is running good (you said it is) that eliminates a lot of the USUAL SUSPECTS, and leaves a dead O2 sensor as the most probable cause, or a bad O2 sensor heater relay or bad O2 sensor wiring, or all of the above. Second major possiblity is a bad TPS, but you would notice that in performance too I think.

When the O2 sensor signal is completely dead for what ever reason, the ECU just switches to a rich gas guzzling mode cald open loop that runs great but eats gas and eats Cat converters.

I bet money on the O2 sensor or its wiring or its heater circuit relay is bad.

The O2 sensor, and relay and wiring can all be tested with a simple analog volt meter. The relay and heater wire voltage can be tested with a digital volt-ohm "multi" meter. The O2 sensor test needs an older style analog volt meter. See some of my prior posts, in particular the "RenX files" thread, or search "oxygen sensor analog meter " and note that yours (94) is a 1.0 volt O2 sensor, not the 5.0 volt sensor used in 87-90.

The idle is definately low, lately it has been in the 200RPM range and has actually died a couple times now.
Anyone have any ideas? Everything checks out with all sensors and wires according to specs. I'm confused and I guess the next step is to check compression, I'm afraid of what I'm going to find now that everything else checks out.

Have you replaced the IAC?

Have you run an error code check?

Have you checked for 12-14 volts on the heater wire to the O2 sensor? It is fed through an O2 sensor heater relay, activated by the ECU on start up. Relay could be bad. Have you checked the O2 voltage with the engine running? Does it oscillate back and forth from 0.1 to 0.9 volts about 1 -2 times a second between the 2 small, usually black wires? What readings are you geting at the TPS on both sides of the TPS?

Partly clogged exhaust, not enough the kill the engine but enough to hurt mileage perhaps?

Leaking fuel injector(s), or low but balanced compression, but that would likely burn oil. Is it using oil???

Torque converter not locking up and or slipping.

Any combination of the above.

What are your grounds reading at the sensor ground to battery negative post with power off? Anything over 1 ohm is not good.