im sitting at 90k mi on my lt, recently it has started surging while accelerating, and when putting into park(as well as when starting), it will rev up to about 1200 rpm before settling down, had it tested and they said it was the TPS, so I replaced that, the issue persisted, and I got a code p2138. have also recently had the trans filter replaced and fluid drained, no obvious damage was found they said at that time. has anyone else experienced this?

 

Since you are coming up to 100K miles, I would recommend you read the thread I linked below (if you haven't already). I don't believe it will help with this problem due to the CEL code you have, but it's still good to keep in mind as you are reaching 100,000 miles.
https://montecarloforum.com/forum/ge...0-miles-46078/

Below is data from the shop book. It sounds like a potential broken connection or bad pedal sensor is to blame. Unfortunately, I am not very familiar with the "drive by wire" setup like what is in your car. Perhaps with this information, someone may be able to chime in with more input.

DTC P2138: Accelerator Pedal Position (APP) Sensor 1-2 Correlation

Conditions for running running DTC:
• The system voltage is more than 5.23 volts.
• The ignition is in the Unlock/Accessory or Run position.
• DTC P0641, P0651, P0606, P2120, P2122, P2123, P2125, P2127, or P2128 is not set.
• The DTC runs continuously when the above conditions are met.

Conditions for Setting DTC:
The ECM detects that the difference between APP sensor 1 and APP sensor 2 exceeds a predetermined value for more than 0.5 second.

 

mine is doing the same it/ mine is throwing a code as a miss on cylinder one if it gets bad. then it clears I did all of the fluids in my monte carlo from the trans to the oil in the engine as well as a fourth tune up in a month. what I replaced in the tune up is wires coil pack brick plugs every thing was done at the dealer. they said it is burning the deposits off the valves. dumb answer I got when I asked it is doing it again after the work. I have about 119k on mine majority on high way. still wondering if it is a valve sticking or a bad computer or sensor doing the misfire. it is frustrating to be honest it is more of a surge and throws that code. then run fine for a week or every other day

 

hi, as an update, had the car in at a local shop, awesome guy, checked out everything he could think of in regards to the problem, first thing was changed the plugs and cables, as the old ones were rather...worn, replaced with NGK plats and ngk cables, had the sensors that were triggering the engine light and they tested fine, he checked all the the connections and they were fine, now about a week and a half later, there has still been no engine light, he hasn't been able to find the problem yet. he has replaced a damaged negative battery cable terminal and fixed a loose ground as well. he has now advised that I should have gm run a tech2 on my car and flash the computer... they are doing this tomorrow, will update.

 

It stands to reason a loose ground and a damaged negative battery cable couple be related. If that loose ground was related to the one of the sensors causing your code, that could have been the root cause.

 

Today I had my car in to GM, they scanned with their Tech2, and it gave the code p0011, which none of the previous scanners have picked up, they said that the leaking water pump flinging coolant off the belt everywhere(and onto the sensor) was the culprit, and repairing and cleaning should fix it.. I have already arranged to have it repaired tomorrow, will update again further, what else can i expect to have a problem here, as well as associated costs to fix?