Rough Idle at Stop sign/light with AC on

[yamaha tech]

I have a 94 Laser that is a DD. With the ac on and stopped at a light, the idle wants to surge up and down, it will drops as low as 350 and back up about a 1000. If you bump it into nuetral, it will steady out at about 750 or so. According to the manual, it should be at 850 with the ac on. I have done all the checks I can think of, no vaccum leaks that I can find, reset the idle speed, checked the timing, replace the ISC controller. I also replace the closed throttle switch, my was bad. So what i am missing?

This is a 94 Laser, N/T, automatic with about 110.000 actual miles on it. Spark plugs are new also. Thanks for the help.

 

[Fatpig363]

Just in case i would check your alternator, might not be a bad idea. most part stores will do free battery and charging system checks. try that

 

[DSM1G90]

You a 4G37, or 4G63 ? For the 4G63 could spell ISC motor isn't doing it's thing too well since it's supposed to keep the idle speed constant when AC is on since it has to ramp up the idle a touch due to the tremendous load the compressor pulls when engaged.

Also, vehicle that old could be that the compressor is getting tired where your AC system needs a 'tune-up' .

 

[Sepison]

could also be a bad cap in ecu