My 82 was doing the same thing. My friend found that the high idle was due to an vaccumm or intake leak.
He found a small broken hose near the driver's side fender well. That hose tied into a bigger hose that is attached to the PCV. As soon as we replaced the small broken hose with a new one the idle dropped down to normal. So check all of your hoses for cracks or breakage. HTH

 

TBI Idle Adjustment 101

The IAC controls engine RPM at idle.

Each TB has an IAC assembly motor that controls bypass air around the throttle valve. A pintle extends or contracts, more air to raise and less air to lower idle.

The ECM monitors manifold absolute pressure to adjust injector fuel delivery as necessary.

The TPS, mounted on the rear TBI contains a variable resistor used to proportion input voltage, based on the throttle angle. The ECM uses this signal as reference for throttle valve postion.

Adjustments
The throtle position of each TB must be balanced so that throttle plates open/are in sync.

***Caution: To prevent ENG high RPM and vehicle movement, turn IGN OFF, with car in NETURAL before connecting/disconnecting IAC valves or installing/removing idle air passage plugs.

Remove air cleaner and air cleaner to TBI gaskets.
Plug vacuum port on rear TBI for THERMAC.
Remove tamper resistant plugs covering throttle stop screws.
Confirm both throttle valves are slightly open.
Block drive wheels and apply parking brake.
Connect a tach.
Disconnect IAC valve ELE CON***.
Fully seat idle air passage plugs***(J-33047).
RUN ENG, stabilize at normal operating temp.
Trans in DRIVE.
If ENG idle speed does NOT drop below curb idle speed, check for vacuum leak.
Remove cap from ported tube on rear TBI and connect manometer (J-23951).
Adjust rear TBI throttle stop screw to approx 6" of H2O on manometer.
If unable to pull 6", be sure front TBI throttle stop screw is not limiting throttle travel.
Remove manometer & cap ported tube.
Remove cap from ported tube on front TBI and connect manometer. reading should also be 6" of H2O. If NOT:
Locate throttle sync screw and collar on front TBI (screw welded to throttle lever).
Grind off weld from screw collar and throttle lever.
Block throttle lever movement to relieve spring force against throttle sync crew. (Levers should not come in contact.) If lever is NOT blocked before throttle sync screw is removed, damage to screw may occur, impairing reinstallation.

Remove screw and discard collar.
Reinstall throttle sync screw with Loctite.
Immediately adjust screw to 6" H2O.
Remove manometer & cap ported tube.

Adjust rear TBI throttle stop screw to obtain 475RPM.
Turn IGN OFF, trans in NEUTRAL.
ADJ front TBI throttle stop screw to obtain .005" clearance between front throttle stop screw and throttle lever tang.
Remove idle air passage plugs and reconnect IAC valves.
Start ENG.
ENG may run high idle until IAC valves clsoe air passages.
Stop ENG when idle has decreased.
Check TPS voltage and adjust as necessary.
Install air cleaner gasket, connect vacuum line to TBI.
Install air cleaner.
Reset IAC motors (drive veh. to 30mph).

[CSM, 1984, 6C14-2]

 

My 82 is idling at about 1,000RPM, even after warmed up. Is there a mechanical way to adjust this on the TBI (like a carb), or is this all handled by the computer?

If necessarry, you can reference the assembly manual. (Waiting to receive shop manual.) Any help much appreciated. I don't want to take it in just do this if I don't have to.

Sincerely,
Ignorant but Learning :smokin:

Before adjusting/sync'ing the idle, you need to verify no vacuum leaks; good IAC motors, and good throttle position sensor (TPS).

If possible, hook into your diagnostic port and check for in/out of, range values.

C'ya
D

 

Thanks for the detailed info. I think this is at the limit of what I'd be willing to try on my own, and I'd feel a whole lot safer doing it in front of someone who has done it before/knows what they doing . . . hint hint, wink, nod . . . beer . . pizza . . . anyone . . . anyone.


But first, regarding checking the out of range values. The diagnostic port is under the ash tray. Is there a scanner for this era, or do I just have to read the codes flashed on the check engine light after following the procedures you have outlined elsewhere?

 

Thanks for the detailed info. I think this is at the limit of what I'd be willing to try on my own, and I'd feel a whole lot safer doing it in front of someone who has done it before/knows what they doing . . . hint hint, wink, nod . . . beer . . pizza . . . anyone . . . anyone.


But first, regarding checking the out of range values. The diagnostic port is under the ash tray. Is there a scanner for this era, or do I just have to read the codes flashed on the check engine light after following the procedures you have outlined elsewhere?

I'm about to head back to Corvette Corrections in Anaheim, next week, for some shop work.

Problem is I have a trial that will take up most my time during February. But let me see how things shape up and maybe we can get together one Saturday, at the shop, in the not to distant future.

I've got a Diacom program to check your parameters.

If you are in a hurry, call Mike (714) 774-4412 and see what he can do for you.

C'ya
D

 

On the whole, the Vette is running adequately, so I'm in no real hurry. There's a kind of set screw on the throttle cable assembly, which after some experimentation, I was able to get the effect of lowering the idle a bit . . . sort of. But it's certainly not ideal or proper.

Therefore, when it's convenient for you, I'd be happy to have your guidance. Until then, good luck with your trial.