Q: Two mechanics have not been able to repair misfire.

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I just moved from California to Arizona and I can't get my car registered in AZ because it won't pass the smog test. In cold weather when I start it up and let it idle for more than a few seconds, it starts missing a cylinder and the "Service Engine Soon" light goes on. If I shut off the engine, wait 10-15 seconds, and start it up again, it stops missing. If I rev the engine after starting it up, it doesn't misfire (or doesn't seem to). Sometime the check engine light goes off after awhile, but lately it's just been staying on all the time. I've had two mechanics in CA attempt to repair it, but they failed. The DTCs are: P0313 Misfire Detectedwith Low Fuel P0492 Secondary Air Injection System (Bank 2) P0491 Secondary Air Injection System (Bank 1)(6) P1349 Misfire Cylinder 4 with Fuel Cut-Off P1620 Map Cooling Thermostat Control Circuit Signal High My mechanic in CA replaced the crankcase ventilation valve, replaced all the spark plugs, and all the ignition coils. Didn't help.

My car has 160000 miles.
My car has an automatic transmission.

Hi there. Check the intake for a possible vacuum leak around the cylinder 4. If there is no vacuum leak around the cylinder number 4, then there could be a burned valve. Check the compression on all of the cylinders and take close attention to cylinder number 4. If cylinder 4’s compression reading is lower than the other cylinders, then you will need to perform a leak down test (requires compressed air and a leak down tester tool). The test will check for any major leaks and exactly where they will be coming from. A burned valve will cause most of the issues with the smog and check engine light. For the code P1620, I recommend replacing the thermostat and flushing the cooling system. Check the fuse and relay to the secondary air injection pump and make sure that they are functional. If the air pump is working, then the exhaust system is taking in too much oxygen from outside the system causing a leak and making the sensors pick up this mixture setting the engine light. If you need further assistance with getting your vehicle to pass a smog test, then seek out a professional, such as one from Your Mechanic, to help you.

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