timing light does not shoot at steady 8
we have 1989 Gmc s15 truck 112k miles
when I check timing instead showing at 8 degree
it flickers between 6 to 10..sometimes 6 sometimes 8 or 10 etc.
same thing with vacuum ..flickers between 14 to 17 etc.
also when we start the truck it vibrates heavily and when stomp on gas pedal vibration stops...when we drive it does not vibrates..so am not sure...if this is due to engine mounts. I also think when engine is warm it does nor vibrates...
changed spark plugs, checked wires for resistance, cleaned cap and rotor...
what should be reason? and what's solution?
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