2009 buick enclave p0300 - p0306 misfire codes

2009 buick enclave 3.6 70000 miles has codes p0300 p0301 p0302 p0303 p0304 p0305 p0306 had new AC plugs installed about 5000 miles ago . history misfire show misfires on all cyls the most are on 2 at 354 and 3 at 234 or something like that the rest are 150 ish up. it has no misfire now cold or warm. as far as i could tell frezfram showed the codes set in the first 60 sec of start up. fuel trims all look good no other codes set. i'm at a loss as to where to start. i have read where a drive belt bad road and i cant remember what else can set misfire codes. pleas help. thanks all

This reads like a carbon buildup problem to me, typical to GDI's. The truly random misfire, the freeze frame... Plus, 70,000 miles is plenty of time for these to gum up their intake valves.

There's various ways you could test for this, like using a FirstLook sensor in the intake, or pull the upper intake to inspect the valves. Honestly, though, when I suspect vehicles have this problem, I just go directly to running an induction service.

I've had success with Motorvac products at work. Also heard great things about BG, like this GDI Intake Valve Cleaner .

I seen a bulletin for this year to replace all the coils and ecm. I don't know if it applies to your scenario... also is this a gdi system?? ive heard these things get carbon on the back of the valves and need cleaned. also have you tried a cam crank relearn?

tyler read my mind with the carbon issue.... or I read his mind..... we posted at almost the same time

cheryl hartkorn wrote: tyler read my mind with the carbon issue.... or I read his mind..... we posted at almost the same time

:lol: Great minds!

Good idea with the cam/crank relearn, too.

thanks for the replies yes its gdi i havent had much exp with them and from what i'm seeing it looks like the only op i there is is to pull the intake and do a manual cleaning thanks again scanner danner did a good thing with this forum (thanks scanner danner)

No problem! I've heard good things about walnut shell blasting as a cleaning process, maybe something to look into.

Let us know how it goes