Rpm idle is to low

[Cntrysthbst]

92 PA with about 132,000 miles. No codes, may new parts. Ac delco plugs, wires, alt, belt, timing, cam/crank sensors, are all new. No erratic idle. At start up all is well till I get to normal operating temp., the rpm reads at 500, it was at 800, maybe 850 before. I've notice at a hard acceration that about a second or so into it I get a boost, like how it's suppose to take off. Sometimes my ac comp won't kick in till I bring it to 750 to 850 rpm.
Please ! Thanks!

[HotZ28]

If you have access to a scanner, check the idle air control motor, (IAC) for proper operation. The IAC is the only control you have for idle speed and it should adjust the idle speed (up-down) with AC on-off. The PCM uses a predetermined idle speed and uses the IAC to compensate for all variables.

[Cntrysthbst]

10-4, will do. Thanks!

[Cntrysthbst]

92 Buick PA - Took throttle body off to clean. I noticed that my TPS is not the original one, and looking closely there's two indend marks on it when I took it off. After cleaning it all up I put it back together and reinstalled the throttle body. Tried to loosen screws for TPS with car running to adjust it and theres a big HOT exhaust pipe that told me different so I had to take the throttle body back off to loosen the TPS. Now I'm ready to adjust it, got the screws half way tight. One light tap towards the drive belt/belts and it's at 1000 rpm, one light tap towards the washer fluid and it's at 500 rpm. what to do, and if I'm even doing it right. I need please! Thanks!

[HotZ28]

The TPS, is simply a potentiometer used to vary voltage. The best way to check the voltage is with a scanner, however if you don’t have one that will give you that information, you can use a DVOM. You can check the voltage on the blue wire, with ignition on and engine off. With the throttle body closed, you should have .37V to .45V. This voltage range should be ideal for idle around 750-850 rpm. The white wire is the ECM/PCM reference signal and should measure 5.0V and the black wire is ground. .The blue wire should measure between 4.1V to 4.5 at WOT.

[Cntrysthbst]

Good deal,

Blue wire w/ ign. on,
closed I got .46v
and 4.10v @ WOT,
White is @ 5.01v.

Thanks!

Testing TPS - Throttle Postion Sensor
for proper voltage.

[HotZ28]

Originally Posted by Cntrysthbst

Good deal,

Blue wire w/ ign. on,
closed I got .46v
and 4.10v @ WOT,
White is @ 5.01v.

Thanks!

Testing TPS - Throttle Postion Sensor
for proper voltage.

The TPS is fine! What is your idle doing?

[Cntrysthbst]

It idles at 500rpm, to low, voltage won't go up to 13 volts till I push pedal up to 750 or so. In another post I posted about the climate control, the ac hasn't worked since. With out the ac on everything is now fine. I noticed on one of the wires connecting to the compressor the coating had melted off about 1/2" up the wire from where it connects to the comp.. I live in Fla. so the ac system is NEVER off. Now that it's off it runs like it's brand new. Idles about 800 rpm, volts go right up.

Could the AC compressor have been causing this problem? Shorted or something?

[HotZ28]

The alternator will not put out charging amps @ 500 RPM! It would be marginal at 750 RPM and if you were using very many accessories while @ 750 RPM, it would probably show negative 12V on your volt meter. Maximum amperage kicks in @ around 1200-1500 RPM.

The wire that connects to the compressor has a diode inline with the hot wire, so it looks like it is a naked wire, however, that is the way it was designed. Take some of the tape off the connector and you will be able to see the diode.

Now, why was the idle low with the AC on? When you turn the AC controller to AC-cool, that commands the compressor to start as well as prompting the PCM/ECM to adjust idle speed up 200-300 RPM. (This is considering normal operating conditions and temperatures). Either the PCM/ECM is not giving that command, or the idle air control is not adjusting counts accordingly. It could also be that the compressor is pulling more of a load than it should, (high head pressure) usually due to a blocked orifice tube. The link below may help you with the AC problem.
*Automotive AC Information Forum*

[Cntrysthbst]

Ok, will do, thanks for the info, I'll check into that link and post back.