Cadillac Repair: 1992 3.1 chevy lumina sedan, chevy lumina, mail delivery

Question
I am at my wits end. The car is used for rural mail delivery. It starts fine and runs fine until near the end of the route (approx. 500 stops) then it really runs rough. If you take it for a 1 or 2 mile run it runs smooth again. It seems to be worse as the weather warms up. I replaced (1) injecter, the fuel pressure reg. and the oxygen sensor. Also I cleaned the throttle body & IAC valve. The Map sensor checks out ok on a scope. The car has 70k on it. I want to thank you in advance for any help you can give me. Chuck

Answer
Constant stop and go driving causes excessive carbon and fuel/air ratio inbalances in the engine and is the worst kind of driving you could ever put an engine thru.

There are just so many possibilities that there is no way to GUESS what it could be without having a hands on professional look at the vehicle.


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