Hummer H3 has a misfire only at idle.
2,335

Asked by Jeff Jan 08, 2021 at 04:49 PM about the 2006 Hummer H3 4dr SUV 4WD

Question type: Maintenance & Repair

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
odometer.

3 Answers
2,335

Jeff answered 3 years ago

All cylinders have 170-180 compression. Battery is 5 months old and tests good grounds are clean and tight.

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10

Guru925J1H answered 2 years ago

It's happened to me on my 07 H3 Hummer. I checked vacuum lines, did a smoke test and found one of my hoses on the evap canister in the back by the rear axle was bad, as well as a vacuum line was cracked. Replaced them and it disappeared.

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