Hi everyone,
I have used the site many times, but this is my first post.

I have a 95, 4.0 ranger, automatic. When then engine is cold it idles great, but when it warms up the idle surges high and low. This only happens when the truck is in park or neutral. If it is in gear the idle smooths out. It also runs smooth while driving. You can sometimes rev the engine and slowly back off the accelerator and the idle stops surging, although it still seem low.

I have read many articles about the IAC, MAF, and TPS but have not seen any articles with my exact conditions. Any help will be appreciated.

Thanks,
Chris

 

Well remove and clean the IAC, have your local auto parts pull the codes, clean the MAF while you're at it. IAC seems to be a common culprit. Let us know how the cleaning goes.

RP
Zach

 

Thanks for the reply Ranger Pilot.

I was looking under the hood at lunch and started messing with some of the sensors. When I unplug the IAC the engine cut off during the low rmp surge. This makes me think the IAC is working. I also pulled the vacuum line from the EGR vacuum selenoid and the idle smoothed out. Some time back I had a 401 code, EGR insufficient flow, and thought it might be the DPFE, but I have been putting off fixing it. Then the idle issue started. Could the EGR vacuum selenoid not apply the right pressure to the EGR valve register and insufficient flow?

Thanks,
Chris

 

I would suspect the DPFE then. I don't have an EGR ('94 model year), so I'll leave this to someone who has more experience with that. Sorry I can't be of more help, hope you get it fixed. You sound, from what I've read, like you're definetly on the right track.

RP
Zach