Stalling and Banging into Gear After TC Lockup

[stocker]

Hey All,

I'm driving an 08 grand prix base model with 142k miles. So a few weeks ago when it was really cold I had the exact same thing happen and it happened again today at -4F. I'm driving mostly highway to work so when it's really cold the transmission doesn't get to 64/71 degrees until I'm almost to work. This issue happened at almost the exact same spot in the road but this time I noticed the TC lock had just recently happened so I'm thinking that is related.

The issue seems to happen when the transmission shifts into it's final gear (not sure what the right term is, OD after TC lockup). My speed is only 40-50 mph so the RPMs drop so low that the engine is really lugging/chugging. Then it shifts out of gear like I put the transmission in Neutral, then every few seconds it will re-engage the transmission with a pretty significant jolt. I've even tried putting in 3rd and 2nd manually while the issue is occurring but it doesn't seem to help. Both times I've slowed to a stop, restarted and it's worked fine after that. The first time the engine completely died when I was coming to a stop.

This last time, right after it went into TC lockup initially, it shifted back out like "whoa not yet" and then the issue occurred a few seconds later.

As a side note, the engine/trans seems to be shifting to the next gear or into TC lockup too soon. The only reason I say this is because it gets really luggy/chuggy/buzzy when it shifts into too steep of a gear and I end up driving around between 1000- 15000 RPMs which seems pretty low.

I doubt it is related but I recently did the steering rack and was moving the downpipe around - I mistakenly installed the metal downpipe gasket by hitting only one of the holes and the gasket ended up crooked. I noticed it shortly after and corrected but now my car smells like it has an exhaust leak. Not sure if this could have anything to do with the issues I'm experiencing.

Anyone have thoughts on:
1) The stall/surge/die issue
2) How the issue could be related to the transmission or TC lockup
3) If this could be related to me moving the downpipe around (I know there are sensors down there)
4) If this is a sign of a bigger problem or anything I should do to try to resolve this

No check engine light either time. Thanks in advance.

[Scottydoggs]

if you have a scanner scan it for codes before you turn it off and re start it to keep going on your way. some things is resetting when you re start it im guessing.

trannys can set a pending code, but it can clear if you turn off the key.

[stocker]

I don't have a scanner unfortunately. Is there one you'd recommend? Is it just an OBDII type with an app on the phone or something more expensive?

[Scottydoggs]

you can buy a hand held obd2 scanner for like 20 bucks, or get a torque app if you got a droid phone or tablet.

[stocker]

Does the torque app still require some kind of plug in device in the OBII port?

[stocker]

The last one I used was a handheld at the auto parts store, the guy said I needed a CEL to be on for it to display and codes. Would either a hand held or torque app be better for capturing a pending code? Thanks,

[Scottydoggs]

yup. a elm 327 blue tooth adapter, theres a few brands out there that do the same job and work with the t app.

then theres some people who have issues with it working on their car but it works on other cars, seems to be a crap shoot, mine works fine for me. its plugged in all the time too for the last 4 years.

[stocker]

Also, I think I was wrong in referring to the downpipe which is actually the catalytic converter. I thought the resonator was the cat.

Knowing that, I've been smelling more raw exhaust in the cabin - could I have put the seal in backwards that goes between the cat and whatever is upstream - or bent it? Does anyone have a diagram/exploded view showing the proper orientation of the metal seal at this location?

Thanks,

[Scottydoggs]

so you have exhaust leaks? cause thats the only way your gonna smell it in the car.

engine,> down pipe has the cat,> res part is bolted to the down pipe and part of the cat back

[stocker]

Ok, so the downpipe and cat are part of the same assembly. I was close then. Yes, I have an exhaust leak after removing the top of the downpipe during my steering rack.

I am concerned about the thin metal gasket/seal at the joint. I put the gasket back in cockeyed the first time by missing one of the bolt holes. I corrected that but I guess I could have put it in backwards.

I noticed the gasket had some compressible material on one side so I supposed it could be in backwards.

[Scottydoggs]

why you take the down pipe off for a rack swap?

at any rate, un bolt it make sure the gasket is in place, if it is or was the flex in the dp might have broken, the flange parts moves, it can break.

[stocker]

I couldn't move the normal size wrench around in there to remove the rack line nuts and unbolting the down pipe allowed for more working room. Gasket looked a lot like this:

https://www.rockauto.com/en/moreinfo...440276&jsn=325

[Scottydoggs]

lower the sub frame next time. 18 mm open or line wrench fits right on there.

thats the gasket, dont think it matters what way it goes on, if you push it on the studs it should stay put for ya.

[stocker]

Subframe was down and didn't have a line wrench - I assume those are shorter?

Ok, thanks Scotty.

[Scottydoggs]

Line wrench is a box with a open end for the line to pass through. No smaller. Just less chance of rounding the nut.

[stocker]

So the stalling has happened a couple more times recently. It always occurs at very low RPM and low outdoor temperatures.

It seems like the engine thinks no throttle is being applied because the engine seems to be idling at about 1k rpms, then it may intermittently engage and bump into gear. However, it doesn't seem to kill the engine unless I apply some throttle - I've shifted into N and tried to rev it but it sometimes seems to just kill the engine. Could this be a gummed up throttle body ( I cleaned this 2 or 3 years ago) ? What other simple issues could it be on an 08, Throttle Position Sensor or something?

[stocker]

So the stalling has happened a couple more times recently. It always occurs at very low RPM and low outdoor temperatures.

It seems like the engine thinks no throttle is being applied because the engine seems to be idling at about 1k rpms, then it may intermittently engage and bump into gear. However, it doesn't seem to kill the engine unless I apply some throttle - I've shifted into N and tried to rev it but it sometimes seems to just kill the engine. Could this be a gummed up throttle body ( I cleaned this 2 or 3 years ago) ? What other simple issues could it be on an 08, Throttle Position Sensor or something?

Anyone have thoughts on the post above?

[stocker]

I cleaned the MAF thoroughly and cleaned the throttle body recently and there is no change. It seems like the transmission is shifting into too low of gear or the TC is locking up at too low of speed and is resistant to coming out of lockup.

Could this be related to poor performance from the accelerator pedal position sensor? Is there any way to test the performance of the pedal sensor?

[stocker]

Last night I unplugged the MAF which seemed to run slightly better but the shifts were funky. The motor still seems to be shuddering/vibrating more than I'd expect at idle.

I left the battery unplugged over night and when I drove it this morning it surprisingly ran much better! I know this resets a couple of things within the car smarts but what exactly would this have reset?

Are there any other ways I can reset any "learned" or stored information that could help my car relearn based on current conditions?

Thanks to anyone who can provide help.

[Scottydoggs]

un hooking the battery will reset the pcm clearing all codes. what i would do is when it acts up again, scan it running for codes, you might be getting a pending code of some sort thats not fully turning on the cel.

dont turn it off before scanning, that will clear the pending code. so scan it running still for codes.