LQ1 TPS voltages?

[Galaxie500XL]

Still having intermittent high idle problems with my '95 LQ1 Cutlass... Finally got some good information, when the "check engine" light came on a couple of days ago. Code was for "LOW TPS voltage".

 

Checked the wiring (CK416-417), and haven't found any problems. I appear to have a good 5v reference voltage, and everything else looks good.

 

Scantool says otherwise. Sensor voltage is consistent at .51 with my foot off the throttle, but the computer is seeing this voltage as somewhere between 0 and 9% throttle. Sometimes, restarting the car makes the scantool report 0% throttle opening (correct), but the SAME sensor voltage, .51v.

 

TPS voltage is all over the place as the pedal is slowly pressed, down as low as .2 volts at one point, then jumping up and down all over until beyond approximately 20% of throttle. At that point, throttle% and TPS voltage go up steadily as the accelerator is pressed.

 

I recently replaced the TPS, chasing the idle issue, and for a brief time, things seemed better, then started acting up again.

 

Am I looking at a bad TPS, or am I missing something? I'd really like to resolve this before sending the car to have the transmission rebuilt.

[jman093]

TPS voltage should increase smoothly. That TPS is garbage.

[threepointone]

i had a similar problem it sure seemed that my car was much happier with a delco tps over an aftermarket tps

[Galaxie500XL]

That's pretty much what I'm thinking, the TPS, even though just a few weeks old is bad...just wanted to make sure I'm not overlooking something..

[RobertISaar]

TPS voltage should increase smoothly. That TPS is garbage.

 

X2!

 

the ECM calibrates the TPS % every time it's keyed on, basing the 0% value on the voltage it sees during that time. however, if voltage drops below it's detected 0% value, then it will readjust where it thinks 0% is.

 

if it goes so low to trigger the SES however, then that's due to going even further under range than the ECM has been programmed to allow.

 

so, either TPS is junked again, ECM is faulty, or you have some intermittent wiring issues.

[Galaxie500XL]

That's pretty much what I was thinking. I was convinced at first it was likely wiring, but if that were the case, I'd expect to see fluctuations in TPS voltage everywhere, not just in the first 15% or so of thottle opening...but I'm still going to keep a close eye out. However, from what I understand, that first 15% of throttle opening is the place the sensor usually fails. We'll see if there's a change once I replace it.

 

The TPS is a BWD, Advance Auto Parts sells them with a "lifetime" warranty...we'll see. Personally, I'm inclined to buy the OEM sensor, but since Advance already got my money on this 3-month-old sensor, I'll see what the replacement does, since that one should be free.

[mfewtrail]

I just put a BWD TPS on my parent's Regal the other day since I needed one quickly at the time. It works perfectly, I monitored voltage throughout the range of the sensor and it changes smoothly. It's only been on the car about 2.5 weeks or so. Hopefully it lasts a little longer than the 3months you got out of yours.

[Galaxie500XL]

Looks like the problem is solved, it was a bad (3 month old) TPS. Idling now at 725 RPM, and at highway speeds, it's no longer dropping in and out of overdrive.

 

Thanks, all for your help...I wanted to get this fixed before having the transmission rebuilt. I didn't want to take the chance of the car idling at 3,000 RPM, and the transmission guys not having the good sense to shut it down while they have the car.