P0505 idle control malfunction

Need help. Have the dreaded P0505 idle control malfunction on a Durango 4x4, 1999 model (5.2L).

I have replaced the IAC twice, replaced the TPS, took off the Throttle Body and cleaned it. Replaced the throttle body gasket and still nothing.

After install of IAC, engine peaks and drops around 700rpm. Test drive thee car, and then the idle is more like 1200-1500rpm.

I have deleted the code from the car multiple times, but it quickly comes right back on.

Any clues? I do not have any vacuum testing equuipment. So I would have to take it to Goodyears, or somewhere to have that done. No obvious vacuum leaks, and no obvious electrical shorts.

Thanks