Shawn M

[S Mitch]

Looking for advice, just rebuilt my 2000 chevy 5.3l. The idle is rough. I have looked for vacuum leaks and could not find any. I looked at the timing and it is at 8 to 10 degrees. When I put the engine together I lined up the marks on the sprocket as directed, top at 6 'o and bottom at 12'0. I also conducted compression check to make sure for leaking heads and such. My compression was at 125 with no leak off.

[CamGTP]

Need to be looking at data from a scan tool. Watching fuel trims to see if they are really high still to indicate a vacuum leak or low fuel pressure.

 

Could also be a bad IAC or something with the MAF but we are only guessing. Idle ignition timing on a scan tool should show around 20ish at idle give or take a few if everything is working right.

[davester]

did you rebuild it to stock?

all the exhaust manifold bolts are present and you put new gaskets/seals in the manifold to exhaust pipe joints?

[S Mitch]

I did put a larger cam in. I did a full replacement of gaskets and seals. 

[S Mitch]

The scan tool shows' full pressures are good. Both rails. I looked for vacuum leaks and cold not find any. I am starting to lean towards a timing issue. 

[CamGTP]

Well no wonder it runs rough, you put a larger camshaft in there.

 

You need to get the vehicle tuned for the camshaft change.