Hummer H3 has a misfire only at idle.
I have a Hummer H3. It has a misfire at idle. Code P0300. Misfire counter
tells me it is on cylinder 4. Checking PIDs it shows miss on cyl. 4 only at idle.
New plugs moved coils around and checked injector balance. I found loose
intake manifold bolts. Replaced intake manifold gasket, manifold surface was
flat. Cleaned throttle body. Misfire goes away at about 900 rpm. What am I
missing that could cause a misfire at idle? Has 160,000 miles on the
would definitely check the Grounding at the battery, and after seven or so, will stop taking a charge and run at reduced capacity~ get a new battery with fresh ground connections and give 'er a whirl then~
What is the compression on that cylinder compared to the others? You may also want to run a leak down test.
All cylinders have 170-180 compression. Battery is 5 months old and tests good grounds are clean and tight.