2009 Camry LE 2.4 4cyl. Used high and low manifold gauges to check pressures. Outside temp was about 70. Humidity was about 45%. Low read 24 and high got 140. Car cools down great, maybe too cold. In park and idling, olnly when the AC is on, or if the AC compressor is commanded like when the fan setting is for defrost, the RPM needle jumps between 750 and 400-500 for a few seconds, and the car vibrates/shudders vigorously, then it returns back to 750. This back and forth jumping of the needle happens constantly, about every 10 seconds. I cannot tell if the AC compressor is short cycling or on all the time, but i do not believe mine has a clutch. It is a new compressor installed last year at mileage of 270k and now i have 321k, mostly highway miles. I have already had the throttle body replaced. I am looking for advice on what my issue may be, because I don't think this up and down is normal. Thanks!

 

The idle should increase when the A/C clutch is engaged. If it doesn't then could be the A/C amplifier, A/C control assy, compressor lock spend sensor, compressor relay circuit, ECM, wiring, .