2001 Grand Prix SE High Idle and late shifting too! {Must have taken a fit, It's OK now}

mrbreezeet1

mrbreezeet1

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Aug 4, 2021
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2001 Grand Prix SE with 3.1-liter motor.
After I started my Grand Prix when cold, and drove it about 30 miles, and came home, it started idling high, around 1500. After it started idling high it started shifting noticeably late. If I shut the engine off and immediately restart it, it started idling fine again temporarily. But I was sitting there in park, with a normal idle, but all at once, she would kick up to high Idle again. Almost felt like the older cars did, when say, you would turn the A/C on, or a high electrical load.
Engine had normal power and runs smooth and idles smooth.
It had/has no codes.
I had just changed the oil, thought maybe l bumped a vacuum hose off or something, but l drove it right after the oil change, and it idled and shifted normally that day.
IDK? Must'a took a fit yesterday? I opened the hood and did a good visual inspection, saw nothing amiss. Took it for at least a good 20-mile drive, everything is acting normal ATM.
 
I once got that with my 03 sierra after taking it out of storage with 34k miles on it back in 2015. It went into high idle mode then when driving it it went into low power mode close to home. I made it home but very slowly and figured it might be a one off thing or not. After an overnight battery disconnect and reconnect it never once did it again after 200k miles later. Odd.
 
Unless my CTS is/was on the fritz. I would have thought it would set a code, unless I didn't run it long enough.
I didn't check the temp with my Torque Pro app yesterday when it was acting up. The temp on the dash showed normal.
Does the 2001 Grand Prix have a Temp sensor for the ECU and also a temp sensor for the dash gauge?
 
IDK about the base issue - sounds like a transient thing as noted, but since you mentioned shifting it occurred to me to mention this as an aside.

Do you service the ATF periodically? My mom had one of those in the past, an 01 GT Coupe. We all really liked the car. I recall it really benefitted from a pan ATF drain/fill (nothing excessing, just like every 30k or so). The shifting would firm up noticeably and at a more appropriate shift point slightly lower IIRC.
 
Oro_O said:
IDK about the base issue - sounds like a transient thing as noted, but since you mentioned shifting it occurred to me to mention this as an aside.

Do you service the ATF periodically? My mom had one of those in the past, an 01 GT Coupe. We all really liked the car. I recall it really benefitted from a pan ATF drain/fill (nothing excessing, just like every 30k or so). The shifting would firm up noticeably and at a more appropriate shift point slightly lower IIRC.
Click to expand...
I've only had it about 2 1/2 years. I haven't serviced the trans yet. I have everything ready to service it, and a shift kit and new magnets.
 
Found a GM coolant sensor on RockAuto for about $24.00, in case I find I need it.

ACDelco GM Original Equipment 213-815 Engine Coolant Temperature Sensor​

 
Took it for a good ride, and came back home and let it Idle, high idle presented itself! But this time kicked on my CEL. Have a code P0121!
I want to do a few more tests, and maybe clean my throttle body, and see what I get.
But I am maybe leaning towards the TPS itself, because Torque Pro is expressing the TPS values in percentages. {I can't seem to change it to voltage} So at idle, engine running, one time I am getting 0.39% shut motor off, Key On, floor it, reading 100%.
Start motor, idling, this time it's reading 0%. Next time, 0.39% next time 0% and so forth.
What say you all?
Screenshot_20231007-194245.jpg
Screenshot_20231007-194013.jpg
 
mrbreezeet1 said:
Took it for a good ride, and came back home and let it Idle, high idle presented itself! But this time kicked on my CEL. Have a code P0121!
I want to do a few more tests, and maybe clean my throttle body, and see what I get.
But I am maybe leaning towards the TPS itself, because Torque Pro is expressing the TPS values in percentages. {I can't seem to change it to voltage} So at idle, engine running, one time I am getting 0.39% shut motor off, Key On, floor it, reading 100%.
Start motor, idling, this time it's reading 0%. Next time, 0.39% next time 0% and so forth.
What say you all?
View attachment 182408View attachment 182409
Click to expand...
Check what voltages you are getting on each wire going to the TPS. I think one is a 5 volt reference and one is a ground. Probably a signal wire too. How many wires going to it?
 
wtd said:
Check what voltages you are getting on each wire going to the TPS. I think one is a 5 volt reference and one is a ground. Probably a signal wire too. How many wires going to it?
Click to expand...
Didn't unplug it yet, pretty sure it's a 3 wire.
It was dark by the time I got back home. Would almost have to be. I'm sure your explanation above is correct.
Again, would almost have to be. I will check for 5 V reference and ground, and I am 99.9% sure the reference wire is working going to the ECM because I am seeing either 0 or 0.39% at idle and 100% at WOT!
I'll do a good visual on the wiring and the connector too!
 
mrbreezeet1 said:
Didn't unplug it yet, pretty sure it's a 3 wire.
It was dark by the time I got back home. Would almost have to be. I'm sure your explanation above is correct.
Again, would almost have to be. I will check for 5 V reference and ground, and I am 99.9% sure the reference wire is working going to the ECM because I am seeing either 0 or 0.39% at idle and 100% at WOT!
I'll do a good visual on the wiring and the connector too!
Click to expand...
Your 5 volt reference should be 5 volts at all times and won't fluctuate as you move the throttle. Your signal wire is the one that will have the varying voltage as you move the throttle. The signal wire should probably show around 500 mv at idle and go up to close to 5 volts at wide open throttle. Yours is showing percentages instead. Since yours is not consistent at the idle position because of the 0% and 0.39%, I would say your TPS is bad. I would say your signal wire is good since you are seeing varying percentages as you press the throttle and the scanner is seeing that change.

I think typically, the signal wire will be the middle wire in the connector when you go to test the wires and the other two on each end.
 
mrbreezeet1 said:
Didn't unplug it yet, pretty sure it's a 3 wire.
It was dark by the time I got back home. Would almost have to be. I'm sure your explanation above is correct.
Again, would almost have to be. I will check for 5 V reference and ground, and I am 99.9% sure the reference wire is working going to the ECM because I am seeing either 0 or 0.39% at idle and 100% at WOT!
I'll do a good visual on the wiring and the connector too!
Click to expand...
I was going to say the idle air control valve, but TPS when you're getting screwy readings (and a CEL), then ya.. definitely check that!
 
wtd said:
Your 5 volt reference should be 5 volts at all times and won't fluctuate as you move the throttle. Your signal wire is the one that will have the varying voltage as you move the throttle. The signal wire should probably show around 500 mv at idle and go up to close to 5 volts at wide open throttle. Yours is showing percentages instead. Since yours is not consistent at the idle position because of the 0% and 0.39%, I would say your TPS is bad. I would say your signal wire is good since you are seeing varying percentages as you press the throttle and the scanner is seeing that change.

I think typically, the signal wire will be the middle wire in the connector when you go to test the wires and the other two on each end.
Click to expand...
That's what I'm leaning towards.
Do you know if Torque Pro is able to read the TPS voltage's as well, or would I need to use a Multi meter?
I know the old OBD1 scanners read the TPS values in volts.
It was the same then too. About 1/2 volt at idle, and about 5 volts at WOT.
wtd said:
Since yours is not consistent at the idle position because of the 0% and 0.39%
Click to expand...
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Agree.


None the less volts or percentages, they are not consistent!
 
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mrbreezeet1 said:
That's what I'm leaning towards.
Do you know if Torque Pro is able to read the TPS voltage's as well, or would I need to use a Multi meter?
I know the old OBD1 scanners read the TPS values in volts.
It was the same then too. About 1/2 volt at idle, and about 5 volts at WOT.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Agree.


None the less volts or percentages, they are not consistent!
Click to expand...
I'm not familiar with Torque Pro so I don't know if you can change the readings to voltages. I would use a multimeter to do any tests.
 
wtd said:
I personally only like to use factory parts when it comes to sensors or engine management electrical components if available but that one may be okay.
Click to expand...
I know what you mean.
I'm somewhat curious too.
They say these WVE are actually pretty decent.
It's the old Wells company for what it's worth 😱
 
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The best warranty is the one you don't need!
Conversely, WVE actually offers the best warranty!
 
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