Idle increase

[boat196]

1970 Corvette (7040207) it recently started to increases idle speed from 800 rpm to 900 rpm. After the motor comes up to operating temperature. I notice this while I’m out driving, and when I come to a stop. I’ll tap the throttle with no change in higher idle speed.

Bob

[Kenth]

Check for misaligned / jerky fast idle cam, idle-turn screw or choke pull-off.
Check the function and adjustments of all possible solenoids on the carburetor.
Check the function of the choke / bimetal and that the flange gasket is correctly mounted or broken.
Also check for broken / detached vacuum hoses at the carburettor and leaking / broken valves and devices at the other end of the vacuum hoses from the carburetor / intake.

HTH

[Cliff Ruggles]

If you don't find the issue there check the timing.  The mechanical advance part of the distributor may be allowing a little timing in at idle speed causing the increase.  I see this a LOT with vehicles brought in here to custom tuning having similar issues......