Thanks for the reply! Nope, check engine light did not come on at all. It felt a lot like the cylinders were misfiring. The strange thing is that it was under acceleration. I went thru a second stoplight and put the gear in neutral and pushed the gas pedal and it was fine - no stumbling or hesitation. But when I put it in gear it did the stumbling/hesitation thing again. When I got to Staples and shut the engine down I was afraid it would give me a check engine light when I start the engine up again but as I said it seemed to be fine aftewards. My spark plugs are new as well as the cap and rotor (all Volvo branded items). My mechanic said the wires were okay. BTW, my mechanic only works on Volvo's but he can't seem to pinpoint the cause. You think its the spark plug wires? Could it be a bad camshaft position sensor? Or maybe even a bad ignition coil? What else could cause such a thing? I'm running out of ideas and I really thought that replacing the fuel pump and filter would eliminate the problem but its apparently still there. I don't want to keep throwing money into this car to find the problem. Its raining here today and I'm afraid the engine will do the same thing again today. I'll post an update.