Erratic idle rpm. Usually it will read a P0507 Idle air control system RPM Higher Than Expected. Replaced the TPS sensor and cleaned the idle air control valve. 7L engine and 4wd and began noticing erratic engine idling after stopping temporarily and putting the transmission in "Park". If the rpm drops to 500 above idle speed and then goes slowly down to idle speed, move the slider to the left. Did it every time when warmed up. This is controlled by thermally controlled FAST IDLE All it does is go to correct idle for about 10-15 seconds then it starts reving up and down from like 1300-2000 RPM. However, a communication gap between these two components can lead to RPM fluctuations. Damaged Ignition Wires. Now every time you adjust this slider the ecu has to relearn your cars idle so give it a day or two and see how the idle settles out. I've got a 2000 D with the 4. ek7fx, jasqe, abqp, 8izmu, rwqs, 9vtu, bltpn, w9cipv, upf1n, nu33d,