Hi, I have a 91 grand prix 3.1 v6, my problem is when the engine is warm and you drive over 40 mph the engine starts hesitating, if you let off the gas it will level out and also if you go faster, however as soon as you drive steady it starts again, no engine light showing, I have changed plugs, wires, fuel filter, checked all fuses. I took it to the shop and the machine said the car was running lean and that was all. Anyone have any ideas why it would run lean or what my problem could be? any help would be appreciated oh yeah also when you drive it and stop the engine seems to lope, but when put in park it quits it and idles fine. the car does start up easily and will drive fine until it warms up