My G runs great. But 1st time I let someone else drive it, it throws P2135 and limps all the way back to my driveway.
I was perplexed and embarrassed. So I tried to drive it about 30 minutes later, and it runs great for me. Engine light is still there, but I can't reproduce the limp mode.

After thinking about it A LOT, I have a theory...

The person whom I let drive it was very very out of practice with stick shift. He killed the engine twice looking for the clutch as he was trying to back out to the street. And several other times he came darn close to killing the engine before he finally got moving. It was when he finally got moving that it threw the P2135 code and went into limp mode.

Q: is it a reasonable theory that there's nothing wrong with the car, it's just that all that stalling/dying upset the ECM? P2135 means ECM is getting weird readings from TPS. Maybe him having the gas pedal halfway down, but then dumping the clutch and killing or nearly killing the engine several times made the ECM think there's something wrong with TPS?

Like I said, I can't reproduce the limp mode. It runs great for me (but I'm good with the shifter). Check engine is still there, but if my theory is right, the CEL will shut off any time now and this will just go away.

What do you guys think? Should I wait it out before tearing into the diagnostic procedures?

 

I agree, sounds like a (hopefully) non-issue. Try running it through the throttle relearn procedure.

 

Clear the code and see if it comes back, that can be caused by either the throttle position switch OR the accelerator pedal position switch.

Something else is to physically check the wiring for the throttle motor, when you stall out an engine it shakes the whole thing pretty bad and you might have a motor mount that's already on the way out and the shudder from multiple stalling caused it to let go and is doing bad things to the wiring harness.

Motor mount is pretty easy to diagnose with 2 people, or if it's just you set up your phone camera nearby on something stable (not the car) to record a video of the engine bay while you set the e-brake, put it in 1st gear and give it a little clutch and throttle (do this in little increments not just once) to torque the motor, then do the same thing in reverse. Watch the video and see how much play there is, should be VERY little even on the OEM rubber mounts.