2000 Altima Cylinder Misfire

[SaturnAscends]

I a m having a very similar problem Factual. I drive a 2000 Altima and my fourth cylinder is misfiring. Most of the time what happens is at a stop while idling my rpms jump rapidly and my car pulsates/jerks as the rpms rise and rise then fall. I have had the sparkplugs and wires replaced, I have had the valve gasket cover replaced as well. I had that thing where they run the chemicals through to clean the fuel lines and all that stuff. i dont know waht to do but it is killing my gas mileage and as a result, my bank account. The fourth cylinder is a mighty pain in the rear. Please help

[Ramius83]

As a precaution, try the following diagnostic method. Go to your local autoparts store and buy some Carbuerator cleaner. With the engine running, spray the carb cleaner on the intake manifold where it bolts to the head near cylinder 4 (you are trying to spray on the intake manifold gasket). When spraying it, take note if there is a change in idle. If your idle does change, then your intake manifold gasket is leaking and air is entering the system, which will cause a lean condition, and furthermore, a cylinder mis-fire.

[SaturnAscends]

I will try that thanks

[SaturnAscends]

The only problem is that the idle changes all the time. Because it fluctuates sp constantly spraying the fluid wont show me anything. Another interesting point is that while I sit idle and the rpms are jumping and the car is shaking I can turn on the AC and the rpms steady and the idling stops. I dont know much about cars but sometimes when the AC is turned on I can hear it click off (I guess it has gotten cold enough) and the rpms start jumping and the car starts shaking again.