Welcome to the Corvette Forums at the Corvette Action Center!

'84 corvette- Throttle Position Sensor (check engine code)


Well-known member
Oct 10, 2002
1984 Gunmetal Met

I have a'84 corvette (sincenew, 37K miles) – Last Sat, when starting the car, and turning on the AC, Ifelt the RPM’s fall off, and then the check engine displayed on the dash.

Using atwo pin connector, with the ignition on but the motor not running, I pluggedthe 2 pin connector into the OBD port.

A ThrottlePosition Sensor (check engine code) = 21 displayed.

I disconnected the neg battery, and reconnected the battery40 min later. Drove the car 10 miles without the AC, and check engine did NOTcome on.

A week later I drove the car to a local car show, 5 miles,and no problem. Then when I started the car to go home, at start-up, withoutthe AC running, the engine lost some RPM’s and the check engine light displayedon the dash.

I replaced the Throttle Position Sensor (TPS) 5 years ago(about 1k miles).

From what I read, if there is a voltage cutoff the TPS willtrigger a error (21) code.

I’m wondering if there is problem with my fuel filter (replaced5k miles ago) or my fuel pump (original)?

All comments are welcomed. . .
Code 21 is TPS signal voltage high. Have you verified that the TPS voltage at idle position is very close to 0.525 v. on pin B, with ground probe of your DVM on pin A? (Per '84 FSM, pg. 6E2-68.) The voltage should rise smoothly to a full throttle voltage of about 5.0 v. (FSM pg. 6E2-66)

You are probably aware, this testing is with the ignition on, but the engine not running.

This test does not guarantee that you have a good connection of the TPS pin B circuit to the ECM. That's a bit more complex. Is your TPS connector in good shape? I hope you have a FSM.

I don't understand your question about the Code 21 and your fuel system.


Corvette Forums

Not a member of the Corvette Action Center?  Join now!  It's free!

Help support the Corvette Action Center!

Supporting Vendors


MacMulkin Chevrolet - The Second Largest Corvette Dealer in the Country!

Advertise with the Corvette Action Center!

Double Your Chances!

Our Partners

Top Bottom