. . . . 2007 nonturbo base model automatic with 120,000 miles. Car runs great with the air conditioner off, but it drops to 300 RPM occasionally when the AC compressor kicks in. Has a new tuneup with plugs, wires, and coil. I have changed PCM‘s with a known good one and it still happens. It seems to be temperature related because when the car is cold, it does not start the miss until 4 to 6 minutes after it is started. . . .

You need to check the suction and discharge pressures on the air conditioning system when the compressor is engaged. Maybe the system is overcharged which would cause a drag on the engine? Maybe the compressor is failing and dragging down the engine?

. . . . I have also run continuity checks between the clutch/pressure sensors and pcm. I’m at a loss right now so any guidance and help would be appreciated. . . . .

Between the clutch / pressure sensors makes no sense???

 

Between the clutch / pressure sensors makes no sense???

Sorry, I checked continuity between the PCM and clutch, PCM and the low pressure sensor, and between the PCM and the high pressure switch.

 

It may not be an A/C component at fault.
I had a similar issue with a 92 Daytona. It turned out to be both a partially shorted cooling fan motor, and an intermittent short in the fan harness. Replacing the cooling fan and bypassing the fan harness with a separate relay and wiring fixed it.
What was happening is that the cooling fan comes on when the A/C is turned on, so it would happen not only with engine warm, but on the highway when the A/C compressor cycled. And the short circuit was so bad it dragged the battery voltage down to about 10 volts instantaneously, then it would snap back up. Took 4 months to diagnose fully and repair.
To test this, unplug the coolant temp sensor at idle and see if the car stalls when the fan turns on. Then if you have access to a clamp ammeter, see how much current the fan draws when it turns on. For me, it was a 36 amp spike and 13 amps steady-state. When I replaced the fan, these numbers dropped to 1/3.

 

Thank you guys for the replies and helping me find the problem. It turns out that it was the cooling fan. The previous owner had overcharged the system because there was over 130 pounds of pressure in the low port before turning the AC on. I reclaimed the 134a and there was 28 ounces in the system, which is 10 ounces more than was required. When I reclaimed the 134 an and there was 28 ounces in the system, which is 10 ounces more than was required. When I started charging the system, I noticed that the cooling fan stopped working about three minutes into the recharge process. That is when the engine started stumbling again. It looks like the fan assembly has been replaced, but the two relays are original equipment. I’m going to replace the relays and see what happens before replacing the entire fan assembly. Thanks again for the replies and the help.

 

I'd also check the Idle Air Control (IAC) Valve. It bleeds extra air into the intake to bump up the idle, which typically happens when you activate the air conditioning.