I have a 2005 Cobalt SS/SC with GM Stage 2, KN Typhoon, and reemed out cat.

I had my throttle body port and polished. When I re-installed the TB the car would start and run for about 30 seconds and run just fine. (with the exception of higher idle which I found out about after doing some reading on PnP) After that first 30 seconds the car would begin to idle erratically and would barely run. The idles bounces around from about 5 rpm to 1500 rpm. The two codes that popped up were p0507 and P0121. While the TB was being PnP I installed a mechanical boost gauge because the junk factory one quit.

I have checked all the connections to the TB and the vacuum line I spliced into to make the connection for the gauge. The gauge works and shows normal vacuum at idle like my old gauge did before it broke so I'm pretty sure there isn't a vacuum leak because the problem doesn't start at initial engine start up.

From the research that I have done it seems that the P0507 code is triggered from the higher idle and the P0121 is set by throttle blade angle being greater than or less than it should be. So the two codes are related to each other.

So does the car need tuned or am I having a malfunction in the TB and it needs to be replaced?

Is there anything else I can check or try?

 

I just tried messing with my car again. I found out that if I delete the trouble code it will run fine until the code pops up again. Is the car just in need of a tune?

Also the the P0121 throttle position code quit popping up today only the p0507 code kept popping up.