This 2000 Mustang V6 acts up really strangely when in gear on idle. It does not do this when in Park or Neutral, only when in gear and the accelerator is not in use. It will suddenly rev up from the normal 700 up to 1000, sometimes 1100 rpm.
The air filter is fairly clean.
I have cleaned the Mass Air Flow sensor with brake cleaner.
I have cleaned the Inflow Air Temperature sensor with brake cleaner.
I have taken the Idle Air Control Valve off, cleaned it first with brake cleaner and Q-tips, then later took it off again and dipped it in gasoline for half an hour, then used more Q-tips to clean it better, and finally used some more brake cleaner, so it's quite clean now. I tested it by plugging it in and turning the key to ON and I could see the switch move slightly.
I have also cleaned the throttle flapper with brake cleaner, and it works smoothly.
I have sprayed a soapy solution over vacuum hoses with no apparent leaks there.
The air intake tube moves slightly when the idle goes up (letting in extra air)
I get no trouble codes at all with my OBDII tool.
Any ideas what else could be causing this?