Q: RPM's fluctuate while idling and sometimes it dies. Getting codes for multiple misfires and knock sensor.

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this is an 01 nissan altima. the problem started a week after I bought it. at first just the rpm's fluctuating and the knock sensor code. changed the knock sensor but didn't fix the problem. Mechanic said the valve cover gasket was leaking into the spark plugs, the oil pan gasket was leaking and the front main seal gasket was leaking. I changed the valve cover gasket, the plugs and wires, didn't find any oil in the plug tubes and the plugs needed changed but weren't fouled nor in bad shape, still getting the misfire code and RPM's are still fluctuating and the car dies if I don't put it in neutral and hold it at about 1000 RPM. not sure if relevant to this problem but when going down the interstate I notice the temp gauge fluctuates back and forth from cold to normal. I don't know what else to do and the mechanic acts as if they don't either.

My car has 135000 miles.
My car has an automatic transmission.

Hi there. Check the fuel injectors and see if they are working or not. While the engine is running, unplug one injector harness at a time. If the engine begins to hesitate, then the injector was working. If the engine hesitated even more, then the fuel injector was either not working or there could be an issue with the cylinder. Check the compression on the cylinders and compare them to all 4 cylinder readings. If the cylinders are all low or all high, then that is good, but if all the cylinders are all different, the there could be an issue with the valves or rings making the engine misfire. To determine this condition, a leak down tester (requires compressed air) would be used to check for a leak in the engine. If you need further assistance with your engine misfire, then seek out a professional, such as one from Your Mechanic, to help you.

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