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Diagnostic help. Pcm issue? Other problem?. 07 gxp acting funny

R

Rjohnson07GXP

New member
So I just put on a 3" downpipe and the engine light came on. I had the guy who did my tune turn off the CEL and now my car is acting very strange. While driving it shifts very hard, slow and hesitant shifts from 1st to second and from second to third. Hard enough to jerk my head and body on normal acceleration. In addition to the hard shifting I can feel the engine is very underpowerd and doesn't get up and go like it did before he turned the CEL off. Then when I put it in park it idles very low and rough at about 600 rpms almost on the verge of stalling. When I push the gas to raise the idle there is no response from the throttle whatsoever it doesn't do anything at all. These symptoms all came right after he flashed the computer and took the CEL off. He didn't change anything besides the O2 sensor. He tried a few other things on his laptop and hp tuners but he couldn't figure it out. Is it the computer malfunctioning or possibly something else? Any information is greatly appreciated. My car is an 07 with about 120k
 


I have a 2008 GXP and it idles at 600 rpm. I also drive a 2008 Suburban with a 5.3 and it idles at 600 rpm. it is very typical for V8 vehicles. I would check for an exhaust leak since you just changed your downpipe, you may not have one, but with it is best to eliminate the simple stuff first. the hard shifting could easily be a tuning problem, but there might also be a transmission issue exacerbated by the tune. might be best just to put it back to stock.
 


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