Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP
I have been a professional master mechanic for over 35 years and am happy to help you with this.
I would suspect a vacuum leak entering that cylinder if the compression is good. Get a can of carb cleaner and with the engine at idle, spray along the intake manifold near that cylinder. if the idle smooths out or increases, there is the vac leak. Now keep in mind that you can only test the upper part of that gasket and not the bottom but they are REAL common to spring an air leak between the gasket and the intake and allowing more air into that cylinder and throws off the air to fuel ratio.
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Thanks for asking!