Is it possible for a car with 228K miles to have an exhaust port clogged up causing a misfire on one cylinder? I have a car here thats doing this to me, and I'm being tormented. its either an exhaust flow issue, or its an ignition issue. I suspect it to be an issue of the cat being plugged up on the motor, which wouldnt surprise me. as it is, the car will start fine, but it wont idle right, it'll do this misfire and it does it throughout the rpm range, only running on 2 or 3 cylinders. so far, I've cleaned the EGR pipe, valve, verified all vacuum lines are good, compression is good, fuel is getting to the motor well, firing order correct(checked 4 times) new plugs, fresh fluids in everything. I'm at a TOTAL loss as to what it could be, other than the distributor being screwed up, or the cat being plugged. by how it accelerates in park, I'm inclined to believe its the cat being plugged up.