Help! 81 Corvette idling low and rough.

[JohnnyGordo]

After reading in my shop manual, it says I cannot adjust the idling because it adjusts automatically. The only way I can get the car to idle well is by turning on the A/C, which increases it from 500 RPMs to 1000 RPMs. It idles at 500 RPMs normally and it almost dies. It also idles a little rough. I have replaced the entire ignition system, pvc valve. Can anyone lead me in the right direction to improve my idle. Sometimes when it bogs down and idles rough I can smell gasoline, so it may have an issue with the air/gas mixture, which again is automatic. Once you rev up the engine the mixture seems to fix itself. Any thoughts? I'm getting a little frustrated.

 

[HammerDown]

I have an 81 and yes there is a set screw on the drivers side of the carb > however rough idling and be cause by a number of things. First on the list would be a vacuum leak somewhere in the system > I actually found one on my 81 way down at the transmission > the little rubber hose that connects to the modulator had a split in it.
Also, it could be the air/idle mixture is out. True the computer makes adjustments for this however there two screws front bottom (hard to get to) are those adjustments.
I adjust them the old school way > with a can of starting fluid and the car warmed and idling simply spray a SLIGHT shot of either over the carb > if the RPM's got up the carb is lean > turn out the screws 1/4 at a time.
If the engine bogs down the carb is rich > turn the screws in 1/4 at a time.
The above seems to work quiet well for basic "idle adjustments".

Also...it can be time to rebuild the carb > these floats can go heavy making a rich idle.

 

[22229stingray81]

Could also be a gunked up/stuck EGR valve. Same symptoms as I had before replacement.

 

[RC81]

Plugged fuel filter?

 

[jimbil208]

Try replacing the fuel pump

 

[TimAT]

Your 81 CCC carb has a throttle position sensor (TPS), a mixture control solenoid, and an idle air bleed, along with the idle mixture screws and curb idle screw. It may also have a idle speed control motor (ISC).
The idle mixture screws were sealed at the factory with steel plugs that have to be cut out of the base plate.
you really need the factory service manual to follow and get all the adjustments correct- the sequence of adjustment can make all the difference.
there's also a green connector toward the rear of the engine that's not hooked to anything- a dwell meter on that will tell you if the MC solenoid is doing it's job after the engine gets into closed loop. (ECM controlling with other than the base mapping.)

Do all the basic stuff first- check for vacuum leaks.

 

[jimbil208]

Tim
I do not have an 81 ,I have an 82,I was replying to the thread.
But listening to what he said, I undertand what you said and it is true,but I had a similiar experience with my 82. The may key that he said that I made a suggestion on is the smell of fuel,rich mixture.
I suggested the fuek pump,from experience,and it may be wrong,bue I would make a small wager in it.
Jimbil