My scanmaster keeps reading code 21 which is the high voltage throttle sensor. I checked the voltage which was reading .87 idle and Went past 4.9 on WOT. After I slot the holes and adjusted the sensor It was reading .62 idle and did not exceed past 4.9 on WOT. The code went away then came back on after a hard test drive. What's the deal with this code? Could the sensor be bad I just had it replaced last week. Could it even be the pigtail harness going bad that connects to the sensor??

 

Did you rotate the throttle blades slowly, watching for any spikes as a result of a damaged TPS sensor winding? Did you check the harness connector for cracking or pin damage, that might be making an intermittent short between the gray 5V PCM base voltage and the blue signal wire? What is the voltage at WOT, after the adjustment? Are you sure your throttle blades are not "over-rotating"?

On the 93's the test for DTC 21 was "over 4.5V". Not sure if that carried forward to the 94's. The 4.9V criterion was used for the 96 and up OBD-II's. Don't know what they used in 94/95.

 

Well my TPS is reading .62 idle and 4.9 on wot - but does not go past 4.9. The pigtail and everything else looks good. Should I try setting the adjust. to under 4.5 wot?

 

A faulty sensor ground on the black wire will cause the problem. When you measured the voltages at the sensor, did you use the black wire as a reference or engine ground? If you used engine ground like most people, you could have missed a bad sensor ground on the black wire.

According to the 94 GM shop manual, if idle voltage is over 2.5 volts or if the voltage is over 4.8 with KOEO. It will set the code. The bad part of this problem is the PCM will not apply the TCC and you will not get 4th gear.

What you need to do is monitor the blue sensor wire for voltage with KOEO and wiggle the hell out of the wires from the sensor all the way to the PCM. And don't forget to check the TPS for spikes(as mentioned above) but you will need a scope as it will likely not show up on simple meter.