94JettaGL heat-related bogging/hesitation

Please help. My car has almost 300K miles on it. I bought it new in 1994. The last three summers though, I crank the car up in the morning and drive it to work 20 miles...no problem. I leave work at 4:00 in the afternoon, it's lets say 90 degrees outside, car cranks right up I ride a few miles and get caught at a redlight, it turns green and I go, and the car hesitates and jerks very badly...worse if the a/c is running. Or I can be driving down the freeway at 70 mph on a hot day and pull off on an exit ramp and downgear into 4th, then 3rd and the car will bog down and almost stop unless I down shift to 2nd, dump clutch, and give it gas. If I cut off the car and run in a store and come back out 10 min later, the car many times wont crank. I have replaced the wires, plugs, ignition coil, cap, rotor, pcv valve, and coolant temp sensor switch, coolant, and thermostat. Finally gave up and took it to VW dealership...they couldnt fix it either (surprised???). Someone please help.

Any check engine lights?

normally when it is happening, no engine lights. Today it was again acting up. I turned the car off ran in a store, came back out and it wouldnt crank up...the battery light, check engine light, coolant temp light, and oil pressure light were all on. They do not typically happen when it is running, even when it is hesitating badly.

Since all those conditions have happened, have the computer scanned to pull codes. My quick guess is the EGR valve. The EGR will cause all the stated conditions. I just need further information to confirm it. One other thing. Does the car have after clatter(doesn't seem to want to cut off) when you shut it off?

franco,
Thanks for the response, EGR valve seems a likely cause to me too. I have never replaced one though. There is no "after clatter" when I turn it off. Can I buy something to plug in and read the codes or should I take it back to VW? Thanks again.

Try checking your local auto parts store first for a free scan. They should have an OBD I scanner tool for VW's. If not, you can purchase one on line or return to dealer. The egr valve is a pricey part so a computer scan is necessary first.