87 Jetta hesitation on acceleration

[thebigyank]

I have an 87 jetta it hesitates/sputters. Initially it only did it an the interstate when accelerating, once the car had warmed up. It would only do it after it had warmed up, and if I let off the gas some it would smooth out, but be slowing sown on the interstate, then eventually clear out and run normally. I thought it was the fuel pump, so I replaced that and the fuel filter. That didn't fix it, still does the same thing, but now it sometimes hesitates on acceleration from a stop. Since replacing the fuel pump twice it ran as above, but when in neutral idled at 2000rpm then I parked it and it died and wouldn't restart. Also, the previous two times I drove it when the temp was below freezing it ran without any problems at all. Then today it was a little warmer, and the problems returned. Any ideas?

[denisond3]

I would suspect either a leak in the air inlet duct running from the air filter (and air flow sensor) up to the throttle vavle, or a sticky air flow sensor, or a large vacuum leak. The idle air control valve can stick and get in the way of the car starting, but once its warmed up it should run okay on the highway, regardless whether the IACV is stuck or not.
Also, doesnt your car have two fuel pumps? One under the back seat, and one inside the fuel tank? I think they will run with the fuel pump in the tank not running, but not so well - with some stalling and such. With the car running you should be able to feel/hear the pump under the back seat running, and listening at the fuel tank you should be able to hear the pump inside the tank running.