Help With '85 Corolla Please

[embagel]

For the past three mornings on my way to work, 25 miles one way on back roads, my car has had the following thing happen. I drive for about 12 minutes, with speeds from 0 up to 55mph. I then come to a stop sign, go through it, go down the hill and my car starts riding rough, losing power, very slow accleration, get slowly up to 55mph goes a few minutes, then starts losing acceleration. I have to keep downshifting gears to get the car to accelerate. It is so bad I have to put the hazard lights. This goes on for about 18 minutes until I reach my office. On Monday I took it to my mechanic who put new wires, plugs,rotor and cap on the car. I picked it up, drove the 25 miles home..all seemed fine. But Tuesday when I headed to work, the exact same thing happened, in the exact same place. I took it back to the mechanic and he put a new fuel filter in it. I picked it up, drove home, all seemed fine. This morning, I left home with my fingers crossed, all seemed good, got to the same stop sign..stopped. Went I started accelerating the exact same thing was happening for the rest of the drive to work. I left it in the lot at work from 8:00am until 1:30 and drove it to an appointment, it was fine. Drove it home, it was fine. So it seems like it is sitting overnight, I drive it for 10-12 minutes, and the problems start. But then it sits for five-six hours in the day and it is fine! What could it be?? It has 181,000 miles,4cy sedan FWD. I talked with the mechanic this morning and we are going to do a new fuel pump tomorrow, but wondered if that is what you all thing is the problem? ARe there other things you would check first?? Any help you can give would be most appreciated.

[ems]

Have you had the catylitic convertor checked. Usually when they are going bad the car starts to lose power when it starts to get hot. Good luck

[Twincam.GTi]

Is the Fuel cap / filler area not 'venting'.

Some vehicles need a 'vented' fuel cap. If a none venting cap is put on they will run for about 10-12miles and then lose power or more usually stop due to lose of 'air' creating the vacumn for the fuel system (think i've explained it right ).

[Unity Jon]

according to the 4age workshop manual it will run 'on choke' for 7-12 mins, i dont think this is a coincidence.

I would check your air filter for blockage and dirt and then clean out your fuel filter, fuel rail, pressure guage and return line (back flush the lot to push any dirt back out the system rather than further into it)

whilst the car is runnign 'on choke' it is getting more fuel and less air creating a useable mixture, i reckon when you stop at the junction the engine revs lower and it comes off choke and cant deliver enough fuel and your runnign way too lean.