2002 Dodge Intrepid Very puzzled about this problem.

I have a 2002 Dodge Intrepid with 138000 miles. For about the past week or so, I would be at a stop sign or redlight, and I would start to accelerate and the car wouldn't pick up and go. It would sit and kind of idle along for a few seconds and then it would finally pick up. It almost sometimes does it at random. I thought it was a fuel problem. I bought fuel injector cleaner but didn't help, and today I was told by a mechanic that there was carbon build up in the throttle body. I originally went in there to get a fuel filter changed. He put some chemical in the fuel system and cleaned out the whole thing. There was a lot of carbon coming out of the exhaust. He told me to drive around for awhile and it should get back to normal. I don't know if that stuff takes a certain amount of time to work, but I'm not noticing any change. However, it hasn't been very long since I left the place. An engine light is on too, but I'm not sure if that would cause it to come on. What is the deal?