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Q: Misfire

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My rpm gauge bounces around, doesn't rev when it does, it just bounces. Have a slight popping noise when idle or driving. Popps more when fast exceleration. Not so bad on highway. Compression test is good. I have changed plugs, wires, cap, rotor, fuel filter, idle air control valve. Still have problem. What would be more likely, map sensor or injectors?

My car has 233000 miles.
My car has a manual transmission.

A: Hi there. From the description you have giv...

Hi there. From the description you have given, your vehicle has a combination of problems. The erratic tachometer/rpm gauge could be at fault. The tachometer signal from the ignition module could be erratic and may also be the cause of your vehicle’s drivability issue. The popping noise has me concerned. Even though the compression test has passed. There is a possibility, an exhaust valve is not opening properly (ie; a worn camshaft lobe), pushing exhaust gas back into the intake manifold. This popping noise from the engine sounds like a popcorn machine. I recommend your vehicle’s problems be inspected and diagnosed by a certified technician from YourMechanic.

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