Why does my RPM randomly go up to about 3500.

The problem:

The RPM goes crazy sometimes, it seems to happen most about 15-20 minutes after startup, it runs up to the mid 3000s then goes back to normal after about 10 seconds, then the check engine light comes on. The weird thing is that the light goes off when it happens again and turns back on after it stops.

Other information that might be helpful:

This car sat for 18 years until I bought it and got it running about 6 months ago.

Things I’ve tried:

Made sure that the mass airflow sensor was clean and able to move freely.

Made sure that the throttle position control sensor was bolted down tightly.

Checked the intake manifold for leaks

Checked the wires for all the sensors that I could find.