1994 High Idle...Why?

[CorvetteMark]

I have a 1994 LT1 which has a high idle (around 1500 to 2000 rpms) but not sure why? I have checked for vacuum leaks (but none) and replaced the Idle Air Control. Anybody ever had this problem?..............

 

[Daryllawman]

Welcome to the Corvette Action Center....... I don't have an answer for you on your problem, but someone will jump in here and help you soon.

 

[LT4John]

CorvetteMark,
I had the same problem a few weeks ago on my 96. I reseated all the sensor connectors and the problem went away. The biggest problem with my car is not the sensors, but the connections to the sensors. I just replaced the wires to my MAF to fix a P0100 error. You may try cleaning the throttle body, but be careful on what you use; they make specific cleaners for them.

Good Luck

 

[Dave C. '04 Z06]

Hi idle speed

Have you done anything to the throttle body recently? Maybe put an aftermarket one on or something?

The best way to find out what's wrong is get someone with a scanner to measure your TPS voltage (throttle position sensor) and IAC (idle air control) motor step count. When at idle if the TPS is 0.5-0.7 Volts the the throttle blades are probably in the right position since the TPS on the LT-1 is non-adjustable. If not (if the reading is higher) your throttle is not closing all the way so something is binding. (a cable, or the return spring, etc...)


If the TPS is reasonable (0.5-0.7V) but your IAC step count is below 8-10 then you possible have a vacuum leak.

****
Don't try this next step without a scanner or you'll hose it all up. As you turn it the PCM will constantly try to adjust the IAC so the engine RPM won't change until it gets out of control range. If your idle is high, then it should drop to the correct idle speed when you are adjusting this.
****

If the TPS voltage is high and your IAC step count is low ( as in below 10) then you need to set your idle bleed air setting (or "minimum idle air"). You do this by inserting an allen wrench into the TB right behind where the stop is and turn it counter clockwise to close it, or clockwise to open it. When you do this you must watch the IAC step count with a scanner and set it so that the stepper is open ~20-50 steps.

If your TPS is good (0.5-0.7) and your IAC step is good (20-50) and your still idleing high, the computer is trying to set it there and I don't know what the heck is wrong.


Oh yea, if you don't know anyone with a scanner, then if your a gambling man you can try to turn it counter clockwise and see if the rpm's drop. They probably will. Once it gets to the correct idle speed, turn it about a 1/4 turn more and leave it. The only problem with this is that you might be compensating for a vacuum leak somewhere which, if ever fixed, will cause the car to try possibly to stall on you when slowing down or on startup. Don't adjust it to where the TPS is less than 0.45V however, or the computer could get confused.

Good luck....

-Dave C. '97 Z28
1997 Camaro Z28 w/ 454cid 6spd
1995 Corvette LT-1 w/ 6-spd

 

[Cruise]

Erractic idling

Would this advice, possibly correct erractic idling?

I also have a '94 and my idling is fluctuating up and down ( quite noticeably ).
I have had the TPS and computer replaced, but it is still doing it.

What do you think?