Ever since I've had my 99 Ford KN Laser Auto, I've been plagued with idling issues. When I first got it, it was barely idling at about 500 RPM. I've replaced the plugs, TPS and crank sensor after it shorted out. Now it usually sits around 8-900, except when it doesn't.
At cold it idles at 1500 and doesn't come back down once the engine warms up. However if I cut the motor and restart it, the idle drops back to 8-900. Likewise when driving, sometimes I'll notice the engine running on when my foot is off the accelerator, when I drop it into neutral it's idling at 1500. If I cut the engine and restart it, it returns to back to 8-900.
Any idea what might be wrong with it?