So I recently bought a 1990 ford f150 with only 80,000 miles I thought it was a great truck to invest in but I've ran into some problems. When driving it when I go to shift into a new gear the idle surges to 2500-3000 rpms. That happens right when I push in the clutch. I thought it was a vacuum leak so we looked for one and I found I had a bad plenum gasket. So I replaced that my self hoping it would fix the problem. But it still does it. What should I do next? I've gone through many sensors and it's not giving me any error codes. Please help!
Update: Gave us a Neutral Drive Circuit Open code and a EGR valve not seated/ closed low voltage. Does that change anything?

 

My first guess would be a bad throttle position sensor (TPS) - you can test it - might want to see how dirty the blades on your throttle body are too.

 

The blades on the throttle body seem to be very clean and the TPS checked good we are just running out of things to check.

 

IAC test
then MAF test

I have seen the VSS wheel on 1992 affect this, not sure about your year.
Make sure your battery is up to charge and is charging correctly. Same with some of the switching at the brake pedal and cruise control.

I would check a wiring diagram for your year to see what is in play when you push the clutch in...

1992 the computer matches the RPM to the auto trans to smooth shifts, perhaps one of the 1990 guys can add to what happens with the manual and the RPM match, for your year.


keep us posted,