Hi:

I have a 2003 3.0L 4v 6-cylinder Sable with 112K miles and an odd problem.

Upon start-up if the AC is on the engine misfires. This will happen immediately when the brake pedal is depressed. While driving in traffic and using the brake the misfire continues; once on the highway it stops. If the AC is off it may happen but rarely. I don't know if will occur with heat too. The air filter was recently replaced and for a few days the misfire was gone but has since returned.

Any ideas? Thanks.

Susan

 

have the spark plugs been changed? is the battery in good condition? is the coil(s) good? It sounds like you may just need new plugs and wires. Or maybe just new plugs.

 

The battery was replaced 9/2006, vacuum leak repair 55K miles and the spark plugs have been replaced. I don't know about coils. In general, the car is well-maintained.

 

it could be the ignition module (they usually last at least 100K miles, but not always). It could be a bad spark wire (I had that problem with my 88 Grand Marquis - weak to no spark). I've also had batteries die on my inside of 2 years, so it's worth getting the battery and alternator/charging system checked for proper voltage output. Low voltages can cause issues too. Autozone and Walmart Tire and Lube Express should check those for free. The coils can usually be checked with a multimeter (ohm meter), but finding the readings that your specific car should have can be reserved to repair/service manuals. I would check the battery and alternator to make sure they're ok, then change the wires... then last change the ignition module if nothing else fixes it. Then the coils. But then I have the testing tools, so I would test the coils first.