The ECM used the TPS voltage to determine throttle position. This information along with other sensor data is used to determine dynamic ignition advance and fuel injector pulse width. On 1985-1991(I believe) Corvettes the TPS mounting holes are sloted for adjustability. One of the Torx mounting screws can be removed to verify that the holes are slotted. The TPS connector has the following pin-outs:
Terminal Wire Color Purpose
A Black Ground
B Dk Blue TPS signal
C Gray +5Vdc
The typical TPS base idle voltage readings are:
Purpose Voltage
Stock +0.54Vdc
Performance +0.65Vdc
1. Before adjusting the TPS the IAC pintel must be fully extended to the base idle
position (see "How to Service the Idle Air Control (IAC)" for this procedure).
2. Connect a scan tool to the ALDL or a DMM across the TPS connector Ground
and TPS signal terminals.
3. Slightly loosen the two Torx screws holding the TPS to the TB.
4. Adjust the TPS position for the desired base idle voltage and thghten the Torx
screws.
5. Manually move the throttle to wide open position (WOT) and verify that the TPS
voltage is at or above +4.6 to 4.7 Vdc. Note that a reading of 4.0Vdc or greater is
sufficient to signal the ECM of a WOT condition.
6. If WOT voltage is not sufficient, slightly loosen the Torx screws and readjust the
base voltage moving top or bottom of the TPS.
7. Repeat until the base idle and the WOT settings are adequate.
If the TPS base voltage is set too high a code 21 may be set indicating too much throttle with idle speed below 2000rpm.