I replaced my old TPS and get the following code now:

P0122 Throttle/Pedal Position Sensor/Switch A Circuit Low Input

Does this refer to the TPS, or is there another sensor?

 

From the LT1-specific code list on Shoebox's "Tech Pages":

P0122 Throttle Position (TP) sensor circuit low voltage

Did you clear the stored code after you replaced the sensor?

 

Yes, I tried to clear the code several times, but it wouldn't clear. On a hunch,I opened the TB butterfly setscrew about two turns and then the code cleared. The car runs well, but the idle is now up to about 1000rpms at idle, but without codes.

 

Are you sure you have the TPS sensor correctly indexed on the end of the throttle blade shaft? You usually have to "fit" it over the shaft, then rotate it slightly against the spring pressure to get the holes to line up.

Extending the throttle stop screw wasn't the best way to solve the problem. First, return it to the correct idle, and make sure your IAC counts are in the range of 20-40. Then check the TPS voltage with a scanner or a volt meter. Should be in the range of 0.20 - 0.90V. If its below 0.20 it will set the code for low voltage. Then rotate the throttle blades slowly to make sure the sensor moves smoothly and the voltage increases smoothly with no flat spots, and reaches approx 4.5V at WOT.

If it isn't reading above 0.20V closed, and you have the sensor indexed correctly on the shaft, you may need to slot the sensor screw holes so the sensor can be rotated to increase the voltage to the range of 0.50-0.67V. Have you checked the harness connector to make sure it isn't damaged or making intermittent contact?

 

Great feedback.

I know about iac count, but do not have a way to measure it.

I feel comfortable that the tps is on correctly and that the connection is good.

I can reduce the idle speed by setting the TB butterfly closer to the original position.

How do I measue TPS voltage?

 

Volt meter. With the key on, engine off, pierce the blue and the black wires, with the pins of the volt meter leads. You can also check between the gray and the black wires to make sure you are getting the correct 5V reference signal from the PCM.

 

I not getting good voltage readings when piecing the wire.

I removed the plug to measure the reference voltage, and it was 2.1 volts rather than 5 volts.

Now I need to track down why the reference voltage is low (providing that it was proper to measure with the plug disconnected.

 

With the tps plug disconnected, I hooked up the voltmeter to the plug's grey and black leads with the key on. The reference voltage constantly fluctuated from 1.5 to 2.1 volts. Way short of 5 volts.

Where do I start to trace the reference voltage back to its source?

Thanks

 

The voltage is supplied by pins B6 and B28 on the PCM. Check the black wire first, measuring the resistance between the black pin in the connector and a good engine ground. Should be "0". Then check the voltage from the gray pin in the connector to a good ground, should be 5V. If you get different results on either wire, go back to the PCM and try again.

 

I probed into the black connector on the pcm.

b6 blk read .3kohms
b28 gray (which is brn on my 97) read from 1.1 to 1.3 volts

 

It looks like I nee a new ecm.

1. How can I verify ecm is bad, vrs a bad connection?
2. Where can replacement ecm's be found?

 

local shop price for pcm w/ 1 year warranty is $102 plus $60 gm reflash cost.

I still need to know how to be sure that the pcm is pad, any way to test it?

I'm concerned that it may ave a grounding our power feed issue that is the real cause of the low 5v referenece output.

Thanks,

 

I put the pcm back in and connected everything up. Now I get a tps referenec voltage fluctuation from 4.1 to 4.3v. The car idles properly now.

I believe I'm dealing with some connection/grounding issue rather than a bad pcm.