I have a 2001 Tacoma dbl cab with a 3.4L auto transmission. The A/C clutch will not engage at idle. Idle is back to normal after throttle body, MAF cleaning, IAC replacement and ECU reset. System has been vacuumed and recharged with pressures within specs. It does not appear to be RPM related as it still will not engage when idling at 1500 RPMs at cold start. If I barely crack the throttle the clutch engages. I suspected a bad TPS. When I loosen the TPS and turn it ever so slightly towards the driver side, the clutch engages. I can tighten it down in that position and it will engage at idle as it should, increasing idle as it should. However, after I drive it a little bit it stops again. I replaced the TPS with the same results. If after it stops working, I loosen TPS turn it toward passenger side and then back to drivers side it will again work for a short drive and then stop. It is like the ECU learns its new position. I have checked values with OBD II scanner and all looks well. The CEL has not come on and no DTCs are present. I have racked my brains and cannot figure this out. I have searched and searched the Internet and can find a few others with the same symptoms, but no solutions posted. Save one that ended up being an O2 sensor. They found that out after CEL finally came on with an O2 sensor DTC. I checked voltage of my O2 sensor with scanner. It appears to be giving proper voltage. Any ideas would be so appreciated, please?

 

So I noticed with my OBD scanner that the only values I see out of spec is the idle and advance timing at idle. FSM shows the following:
Idle 650-760 RPMs (truck is running 1150 RPMs)
Adv timing at idle 12.5-22 degrees (truck is reading 10 degrees)

When I slowly crack the throttle, the RPMs gradually increase until the timing adv goes up. Exactly when the timing goes up, the A/C clutch engages. Could I be on the right track here? If so, what would cause the timing to be lower than specification?