Check engine light is on again, and the error code read P0304- Cylinder 4 Misfire. This has been happening for the entire time i have had the car (4 years) and nothing we have done in those years have stopped it. The car runs perfectly fine most of the time, unless i get stuck in 10 mins of traffic, or wait with the car running for a short amount of time, or am going under about 10 miles an hour for more than a couple of mins. The car cannot idle for an extended period of time without the 4th cylinder check engine light coming on. If i'm in traffic i have to get off the highway to get the RPMs up so that it stops running as rough. Most of the time it still doesnt matter the check engine light comes on anysays. About my car... its 97 cherokee country, the recent maintanence we have done just in general were changing the spark plugs and distributor cap (twice in 4 years), replace master cylinder, oxygen sensor, some fuel sensor (not sure) transmission solenoid, brake booster, transmission line (twice), radiator, seafoam treatment, new batteries, and other random maintenance. I know nothing about cars so i don't know what could be relevant but everything i have read about cylinder 4 misfires we have already done and i'm hoping anyone has new ideas. I just want to be able to sit in my car for more than 5 mins without the car shaking and the check engine light coming on. some one please help!