3rdgenfbodyguy!

Howdy fellas, I have a an issue with my 88 GTA 5.0L with the idle. Sometimes when it starts up it will idle at about 1100-1300 rpm's. Sometimes if you shut it off and restart it she'll idle at around 600 BUT if you put it in Reverse or Drive then back in Park it will jump back to 1100 hot or cold dosent matter. To correct a few problems I replaced the vacuum lines, replace the Air Idle Control Valve, Replace the Throttle Positon Sensor. NOW HERE IS WHERE I'M STUMPED, the shop manual and you tube videos show the Throttle Position Sensor adjustment is to connect a volt meter to the middle pin (B) , Adjust it until you achieve a reading of .54 - .56 volts, However I can not get mine above .34 volts. I checked the adjustment screw on the driver side of the throttle valve and thats not the issue. The TPS is new, What would cause me not to be able to get above .34 volts ? Any ideas ? Its driving me nuts.

Aaron R.

I bought a brand new one in an acdelco box last year. It was bad from the factory and wouldn't adjust enough for me to get it set at the right voltage either. Returned it and bought a different brand.

The one from autozone worked correctly for me.

3rdgenfbodyguy!

Hey thanks for the input, I’ll definitely get another new one of a different brand and try it. Do you remember what brand worked for you? I believe mine is a Standard Electric

Aviator857

If you find the right parts counter person they can test it for you before you buy it. Have you verified the input voltage?

3rdgenfbodyguy!

Aviator857, no I have not. I didn’t see anywhere in the manual or on google that I needed to do that but it makes sense now that I think about it. Is the input voltage pin A or C & what should it be? Thank you for your help

Aviator857

Not positive it's probably either 12v or 5v input. Should be in the schematic.

84Elky

TPS is 0-5v, but you may not see 5.0v when fully open, but that's OK as long as it's 4.5v+. Many times, even with Delco OEM replacement, one of the mounting holes needs to be ground out (elongated) to allow 0.54-.56v at closed throttle.

No need to have it tested. Your volt meter won't lie. You should see voltage rise from closed throttle voltage to 4.5+ at WOT with key on-engine off.

Aviator857

Based on what 84Elky said its a 5v input. test the input voltage with the multi-meter it should be within a reasonable range of 5v. Assuming the input voltage is good then do the engine off, key on test 84Elky described to see if the sensor is good. Hopefully just a bad sensor, if so replace and report back.

If the input voltage is bad a few things you can do.
Look at the schematics and see what shares the 5v reference line, if something does unplug it and retest input voltage.

Trace the wire back to the ECU and depin that wire from the connector and with the right probe see what the voltage is at the ecu engine off key on. (you can cut the wire and then solder/heat shrink if you can't depin it etc) I would not jump to the conclusion the ECU is bad though if the voltage is off. The next step is to make sure the ECU has the right input voltages and grounds.

I've also seen something totally unrelated cause the ECU to not provide the right 5v so it can get annoying tracing it down.