A thing that pops into my head might be the timing of the camshaft or a bent valve. I had a bent valve (intake) in my s4 and the check engine light would come on and go off. Got crappy gas mileage etc etc and didnt have as much power, but i was still able to drive it.

I can also speak from my dirtbike tuning. If a camshaft is off one or 2 teeth, it can cause rough starting and dying at idle. I dont know if this helps but it might be relevant.

 

It would be a bummer if the timing chain has jumped a tooth. According to this photo, http://www.minicooperspeed.com/wp-co...-gear-tool.jpg, the gear has 46 teeth (yes, I counted them). That's ~7.826 degrees per tooth.

 

Why does the OP keep trying to cure everything but the most important problem.. the low compression

 

Yes, a compression check would work, too.

 

WOW! Thanks for all the help everyone!!!!

It turns out, its the TMAP sensor that was causing my car to go nuts. Realizing that the compression is bad, it hasn't affected my car in any other way. this is why:

After I successfully got the CEL to turn off the first time, it eventually came back on. Originally I had 2 codes: P0301 and P0172. Well I went through and unplugged and re-plugged a bunch of connections, the throttle body connection, both MAP sensors and such. CEL did not disappear. The next day I went to go buy a Actron OBDII scanner, and it read up with 8 codes!!!!!

I was just thinking "OMFGosh!!!!!" Well I cleared the codes and its driven without a code since!!!! It's been about a week or so now I would say, and this past weekend I did change out my TMAP sensor (since that was how the light shut off in the first place) and STILL have no CELs! Car runs TERRIFIC no hesitation stumbling whatsoever! Granted the compression is a bit off and heading downhill, it was the TMAP that was causing my car to self-destruct and hit limp mode.

Thanks everyone for your help!!!!!

By the way; like I was saying that I got a custom P&Ped head with a NS2 Cam, got the car tuned again. My previous numbers before those two swaps was 197whp and 181wtq on a Dynapack. Dyno-ing on the Dynapack again, i'm doing 225whp and 198wtq. Thats pretty good

 

Congrats!! It is nice to see something like this work out for the best!!
Keep an eye on the compression...you my need to do something in the future, but in the meantime, MOTOR ON!!

 

Glad to hear it worked out.

 

Really decent #'s considering the compression issues.

 

No problem. I am glad you fixed your problem.

 

Thanks so much heavymetal! Indeed great help!

 

I have the exact same symptoms as the OP. I took a voltmeter to my TMAP sensors and found that at idle, it's putting out way more voltage than it should for an idle RPM.

I'm getting a reading of something like 9.5psi in the manifold at idle (from Torque app on android)

Should I replace one sensor first, or both at the same time? Or could this be caused by something else?