BUICK REGAL CUSTOM 3.8 CAR MISSES IN 4TH GEAR.

Do you have a check engine light?

Could be coming from the transmisson-Check the transmission fluid level and condition.Also refer to this walk-thru link of misfires: https://www.2carpros.com/articles/engine-misfires-or-runs-rough

no check engine light. when I put my OBD1 THE FANS RADIATOR FANS START AND DO NOT STOP UNTIL I PULL THE OBD1 FROM THE SOCKET. I have checked all the sensors except the IAC which I will do Tuewsday. All the sensors check okay.
I do have a miss at idle but it is hard to see the engine move as I have replaced all the motor mounts. I have checked all the injectors and all are working and they all have 11.6 ohms.
They all work when I put the stethoscope on each one.
I have checked the ICM and it checks okay. Each spark plug I have checked and all are the same color. I have put new plug and plug wiring on this past week with no improvement.
I have an idea when I take the throttle body off and check the ICA I probably will be my problem. It amazes me that it has so much power when you put it to the floor.
Any help would really be appreciated. Wendell A

Also when the engine is idling and I turn on the ac the engine does not increase in rpm. Wendell A

Triple check the IACV- when the AC is turn On- the idle speed should stabilize not drop due to the extra electrical load imposed-