2001 Pontiac Grand Am: high idle, high rpm shifting

[gustie07]

I have a 2001 Grand Am SE 2.4 liter automatic. Last winter, it started idling high after a cold start (around 2500 to 3500 rpm) and then would drop to 1000 to 1500 rpms within 15-30 seconds. It also started shifting strange, mostly from 1st to 2nd and 2nd to 3rd gears (automatic transmission). The car would rev to 3000 to over 4000 rpms and then shoot into the next gear, unless I babied it and feathered the gas pedal, it wasn't so harsh. I took it into a repair shop, no codes came up and they weren't sure what it was. I replaced the tranny fluid and TPS, neither did the trick. Then I had a "new" used computer put in, which seemed to do the trick.

Then within the last month, it started having the same symptoms again. I did have a code on the OBDII, which was for a small EVAP leak. I replaced a hose (attached to the MAP sensor I believe) and then the TPS (again, even though I had replaced it less than a year ago). Neither fixed the problem. My question then, is it likely that a 2nd computer (PCM I think it's called) go bad in my car within the same year? Or is it something else, even something that could make the PCM go bad in the first place? Any help would be greatly appreciated.

[doctorhrdware]

Or it could be a problem in the wiring. Pull the connectors going to the PCM and check the pins on the connectors for corrosion and on the PCM also. Also check the wiring, it could have a short in the wire harness.

[thephantom1492]

If they replaced the BCM, they stole your money.
The BCM is Body Control Module, and control non-engine stuff, like lighting, security, doors, windows, seats, A/C and so on.

PCM: Powertrain Control Module, this one control the engine and transmission. It also control the cooling fans

EBCM: Electronics Braking Control Module, mainly known as ABS module. It deal with, well, brakes

Airbag: Well, it's the airbag control module.

Cruise control: well, another one that is obivious.


Bring it to a real garage with proper scan tool, they will do a road test and check real time data and see which sensor is faulty. But you might want to check the PCM connectors, this module is located under the kick panel of the driver side. Remove the plastic under the dash, the module is on the exterior wall "up there". Check for corosion in the connectors. You might want to locate the TPS and check it's connector too.

Also, check the MAF sensor, it could be dirty. The Mass Airflow Sensor is there to tell the PCM how much air came in. Wrong data can cause a wide range of issues, including surges...

A note of warning: only use MAF cleaner on MAF, other cleaner can kill it so only do the proper stuff...

[gustie07]

Thanks for the replies. It was definitely the PCM they replaced, with a used one that they took to a dealer and had flashed. When I was having the same exact symptoms last winter, I went to a mechanic and rode with him during the road test. Even he wasn't sure what was going on with the car, there were no codes activated but there were two strange things going on during the road test (the first was that the gear on his reader would show we are in a different gear than the car was actually in, and I don't remember the second problem). Anyways, he figured it might be the TPS or PCM, which he replaced them both. That worked for about ten months.

About the wiring, isn't that something the mechanic would have noticed last winter? If I check it myself, and unplug it, will that screw anything up where I would have to reset everything or take it into a shop to get reset?

And I looked in my Haynes manual and it says it doesn't have a MAF sensor, only the V6 models have it (mine is a 2.4 L 4 cyl).

[thephantom1492]

If you disconnect the battery first, it will be all fine. However be warned that when you disconnect the battery the PCM lose some setting and can take a bit of time to relearn the stuff.

But... Have you checked to be sure that your transmission don't lose oil? Everything in a transmission is oil driven, including the gear shifting. Half a pint lost is what is needed to start to have driveability issues, like slippage in the torque converter... Later on you could lose some gears (due to not having enought oil to shift).

[doctorhrdware]

Originally Posted by thephantom1492

A note of warning: only use MAF cleaner on MAF, other cleaner can kill it so only do the proper stuff...

The MAF cleaner that is made by CRC is good stuff. I have used it and have not had a problem since.

[gustie07]

Does the 4 cylinder have a MAF? My Haynes manual says that is only in the V6 models.

I thought it might be the tranny fluid last winter. It doesn't have the dipstick, so it is a pain to check and replace. I had a shop do it and they said the fluid looked fine and wasn't leaking, so I don't think that is the problem.

I checked the PCM and the wires look to be alright. I think I'm going to go ahead and order a computer (as much as I hate to do it), but it seems to me if it was any mechanical problem it would show up on an OBDII reader? My check engine light isn't even currently on but there are definitely some major issues going on. Before I order a computer thought, can either or you, or anyone else, offer any other suggestions? Could the computer just need to be reflashed? Or would I be expeiencing entirely different problems?

Thanks again for all your help.

[thephantom1492]

I hightly doubt that it's the PCM.

have the transmission fluid level checked.

Also, a good garage would be able to connect a test tool that can actually read live data and they can see what's going on.

Codes ain't the only thing that they can read, every single parameter is on the OBD-II bus! they just need to do live analysis and they can pinpoint many problems.

[gustie07]

Thanks for the reply. But I had the same exact symptoms last winter, and neither shop I took it to could figure it out. They replaced the tranny fluid (didn't help, looked fine and wasn't low), the TPS (didn't help), and finally the PCM (worked, but only for about 10 months).

The first shop had no clue what was wrong with it, so they sent me to a transmission specialist. I rode along with the mechanic while he did a road test, and there were two problems. The I can't remember the first, but the second was that it would say we are in park (or 1st or 2nd or 3rd..) while we were clearly in a different gear. This led to him to believe it must be a problem with the TPS (which it wasn't) or the PCM itself.

I guess all I'm really wondering is could a second PCM (it wasn't brand new) go out in my car within the same year? Or could something else be making it go out?

Thanks for all the help so far guys, this car is driving me nuts.

[thephantom1492]

Could be a faulty shift solenoid in the transmission too.

If one of the coil is partially shorted it will take more current, causing the driver in the PCM to overheat.

I would suspect that the 1-2 solenoid and 2-3 solenoid would be the same, so it could be a good start...

Wire color: at the transmission and after the disconnect plug (so PCM side)
TCC Solenoid: tan and become brown
1-2 solenoid: light green and become light green
2-3 solenoid: yellow and become yellow with black
Those 3 solenoid also use a common red wire that become pink
pressure control solenoid: purple become red/black AND light blue become light blue/white

[gustie07]

Thank you thephantom1492, that is exactly the kind of answer I was looking for when I posted the question, something that might make the PCM go bad in the first place.

I somewhat understand what the shift solenoids are (in the transmission I would guess, sounds expensive), but I'm a little lost with the second part of your post. Am I supposed to check these wires under the car at the transmission ("at the transmission") or check the wires into the PCM under the dash wires ("after the disconnect plug (so PCM side)"). And when I check the wires, am I visually observing something or checking with the voltmeter? Thanks a ton for the help so far. I'm not much of a gear head but I do enjoy learning and doing things myself.

[thephantom1492]

I don't know how it look at the transmission, but I have 2 color table for the wiring, one from the transmission and one after a plug. I gave you both wiring colors so if you want to check with an ohms meter (multimeter) you can check it at any place. My guess is that the PCM side would be easier to access than the transmission.

Remember: before disconnecting the wiring at the PCM disconnect the battery! Once you'll reconnect the battery the car might run weirder due to the PCM that forgot some of the learned car parameters. Don't worry, it will learn them back soon enought. (those parameters include how much gas it need to give during idle and while you accelerate. So you can get rought idling at first, until it rebuild it's fuel table)

[gustie07]

Thank you again for the reply. I will hopefully get a chance to try that this weekend. I feel like this information will really help me get somewhere, so thanks everyone for your help so far. I'll let you know if this helps. In the meantime, if anyone else has any other theories, I'll take all the help I can get!

[uno1111111]

have the same problem in my 2001 grand am 2.4l idles high and shift high just found out today what was wrong with it was the intake gaskets changed them now it runs like new hope this helps

[jessica naviaux]

I have an 02 pontiac grand am v6 3.4 the symptoms are it started high idling and then it progressed to going to over 4000 rpms to get the car to move and then it progresses to get better after about 30 to 45 mins after that time frame it acts like a normal car i do have an 02 sensor going bad PLEASE SOMEONE HELP ME