I've had this car for about two years now, and it's only got 125K miles on it. I've done a pretty good job maintaining it, but now it's doing something that I just can't figure out.

When I first start the car and drive around initially, everything is fine, but after the car heats up and I've driven it for a while, it begins to feel like one of the cylinders is not firing. The engine begins to "rock" every once in a while (once every 3-5 seconds). The exhaust seems to come out in staccato puffs, though it's not smoky and does not smell or anything like that. If I try to accelerate up a hill while this is going on, through the gas pedal I can feel the engine hesitating for a second and then running fine for a second. Sometimes it gets so bad that you feel like you're riding around on a bumpy road or like you're driving in a manual with a kid that just can't get it in gear.

I pulled off the air filter the other day and cleaned the throttle body and linkages with carb cleaner. I pulled a couple of spark plugs and they seemed to look okay -- no oil, just slightly red, not a lot of carbon buildup, etc.

After having driven the car around for a while, the car exhibits this behavior regardless of whether I am stopped, accelerating, decelerating, or in gear or out of gear. I have tried various gas octanes, and have run a few fuel system additives in recent tanks.

The maintenance cycle seems to indicate that the fuel filter should be changed, which I have not done yet. It is also probably due for a spark plug change.

Anyone out there have any idea what might be the culprit? I really love this car, but I'm a college student without enough money or time to baby it like I want to.

I had a similar problem on my 1985 380SE. Problem was two blocked fuel injectors after I ran the gas low in the tank. You could have your mechanic put the engine on an engine analyzer. On my car, the bad cylinders were shown by abnormally high voltage on the non-firing cylinders.

Runs good as new after the 2 injectors were replaced.