Low Idle - One More Time

[enjr44]

I guess I am beating a dead horse; but, will give it another go.

My 4X2, 4.0L, auto trans, 2002 Range has a strange idle problem and I have no idea what the problem is. This started after a 2000 mile road trip where the outside temperatures were in excess of 100 degrees on average. I had a couple of dogs with me so it was left running at idle, with the air on, for extended periods of time. However, the low idle did not show up until after I was on my way back, so I tend to discount the extended idle time. But …

It starts great, idles great, runs great, and does everything else like it has done for the last 12 years. Everything works just like it is supposed to do except now…..once it is at normal operating temperature when you shift from drive or reverse to neutral or park the idle drops from 750 rpm to the base idle (500 rpm) and them slowly (after about 30/45 seconds) returns to 700 or so rpm. This is really disconcerting.

If you shift back into drive or reverse it immediately returns to 750 rpm. It jumps right back up there.

I just can’t figure out what else could be causing this low idle. I replaced the IACV on the off chance; but, I just don’t think that was or is the problem. In neutral or in gear the IACV is responsible for idle speed as commanded by the PCM .

What else could be messing with the idle??? If it is in gear the PCM commands 750 rpm and the IACV does its thing to keep it at 750 rpm. If it is in neutral what else could be causing the lower the rpm? I would think that if you put it in park the PCM should still be commanding the 750 rpm. I just can’t figure this out. I have disconnected the battery several times to reset the PCM and it idle correctly for about 50 miles or so. What would be causing the idle drop and then the slow recovery in neutral?

Anyone have any ideas or a handle on this??

Thanks, Ed

 

[SenorNoob]

Got codes? Bad Crank or Cam Position Sensor? Maybe a flaky Ignition Module? Which if I remember right is part of the ECU by that year model...

Just throwing out some wild guesses.

 

[kevinrca]

Hi,

New to this forum and not certain where to post this but I would like to know if my Ranger is a flat tappet cam engine or roller cam? I have a 1991 Ford Ranger XLT. I need to know if I should be adding a zink or ZDDP additive to my oil if in fact it is a flat cam engine, it's the 3.0 litre Ford Vulcan engine and again, it is a 1991.

Thank you!

 

[enjr44]

Got codes? Bad Crank or Cam Position Sensor? Maybe a flaky Ignition Module? Which if I remember right is part of the ECU by that year model...

Just throwing out some wild guesses.

No codes??? No check engine light though. The rest of the items should show in drive or reverse as well as neutral or park. Guess I am just going to have to take it in and pay for diagnostics.