My 91 740 WGN (non turbo) runs great for about 30-45 minutes, then the throttle gets sluggish. When I try to accelerate it just bogs down and when I let off it picks up a little. I have replaced the plugs, cap, rotor, wires, air filter and done an oil change recently. I just got this car and don't know the history but it was well kept judging by condition. Also, where can I find a vacuum diagram to troubleshot my A/C problem. Any help would be appreciated.

 

Try to feel the Exhaust and see if it feels restricted.

Possible Bad Cat Converter.

 

Checked cat out and it's fine. When the sluggishness starts I can pull over and restart the car and it runs fine for a while, also the rpm's are at about 2K whene I stop. Is this a computer problem?

 

Maybe a Mass Flow.