I got the check engine light fixed and decided to have the gauges I've had installed. I get the car back and the idle goes up and down continuously. I can hear air being sucked in and it is not the intake. Any ideas of what it could be. the gauges installed were oil pressure and a/f ratio and the a/f follows the change in idle from rich to lean back and forth. thanks for any help.

 

its either a egr valve or a throttle position sensor unpluge the clear/dirty clear plug on the throttle body and start it up if it s a 3rd gen for example good luck

 

I have a 92 H23a. I had the same problem. When I replaced the fast idle valve, the problem was gone. It could also be the idle control valve.