Strange idle??

[Bashman]

Just wondering if my X has a strange idle or is it kinda normal. I have a '93 with the 4.0 pushrod in her. She's a ticker/pinger with slight left lean and I noticed today when it's idling, every 5 seconds the rpms increase from 500 to 750 and back again. Possible vacuum leak or what?

 

[TPLYNCH]

What is your climate controls set on? If on anything but panel, the compressor runs, which will affect your idle. Does it do it if it's set to OFF?

 

[410Fortune]

Yah chck and see if the A/C compressor is cycling, if it is then it's an easy fix.

Also search for how to clean the MAS sensor and the IAC valve, a dirty MAS sensor is the number one cause of a surging idle or hesitation.....

 

[Bashman]

Thanks guys! It was the A/C compressor causing the surging.

 

[dannydux]

Strange idle

I bought my son a 92 Explorer, 4.0L about a year ago and had the same eratic idling problem. 500rpm to 1000rpm. I took it in to one of the local shops an had them put it on for some diagnostics. It happen to be the fuel pressure regulator. Its a small golf ball size part mounted on the fuel rail on the passenger side of the engine. The regulator was putting out excessive fuel pressure to the injectors and that was causing the surging in the idle speed. A 90 buck part at the auto parts store. I put it in myself, 2 bolts and a fuel line disconnect