[H-D_Vette]

I recently purchased a 1987 Corvette with a 4-speed and about 111k miles. It was inexpensive and had been sitting for some time. I have been driving it for a couple of weeks after changes all fluids. It runs well except that it typically does not idle down during shifting or if I take my foot off the gas pedal at highway speeds. I need very often to put the clutch in and tap the gas pedal to bring the engine speed down during shifting and highway cruising. I have sprayed the throttle linkagewith lubricant where the cables connect to the throttle body and have sprayed the throttle plate area. this seems to have worked for a short time (not quite sure) but in the long run the problem seems to be getting worse. Do you have any ideas of where or what I should check or try next?

[KULTULZ]

First, remove the throttle cable from the throttle valve and check for freedom of movement in the cable housing. Any binding/sticking...replace the cable and housing.

Make sure the linkage bracket is mounted tightly on the upper plenum.

Check for any binding in the gas pedal (linkage) itself.

Second, remove the air intake and MAF sensor and operate the throttle valve by hand while checking for any binding in the bores. You will be looking for a worn throttle shaft bushing and/or throttle plate sticking in the bore.

It may be sticking because of coke buildup (air flow reversion) or mechanical failure.

You may also have an engine control device (such as IAC motor) malfuntioning. If you cannot find a mechanical fault, have someone run codes for you.