Another High Idle Issue

[BuffaloXplorer]

I sincerely HATE to do this , but after an hour or so of searching i believe my problem is a bit different than the others' i've read.

When i start the X in the AM (it's generally cold), and sporadically throughout the day (regardless of engine/ambient temp) it revs around 1200 rpm (it sounds higher, though). It takes quite a while for it to come back down to the 7-800 or so it normally is, and generally not within the 10-15 minutes i let it warm up in the AM. If i drive it before it settles down, i can actually feel it trying to push through my braking when i'm stopped at a red light & such. Eventually, it will go away, but well after the engine is at proper operating temp, so that has nothing to do with it (?). While it's revving high, it does not surge - it's steady at 1200.

At first i thought it was a sticky throttle body, but i've popped the hood when it's revving high and determined that it is fully closed. I also disco'ed the IAC and it stalled right out. Does the TPS have any effect on how fast the engine runs? I haven't yet taken to testing the components electrically, though, which would be my next step. I know the TPS ideally should be at .96v at idle - what about the IAC?

Ideas? Thanks in advance.

 

[aldive]

How is the thermostat?

 

[BuffaloXplorer]

Coolant temps are right on the money.

 

[mosinman]

run high.

Idle speed is physically set by the IAC, although the PCM does take into account info from other sensors. The IAC is supposed to send a cel if your idle is over 1000. That being said, my IAC went on the fritz and never threw a single code. Cleaning the iac fixed the problem for a couple of months, then it went out completely. Replaced the IAC and all was well again. Wish I would've just replaced it sooner as the idle was smoother than with the old one even after I cleaned it.
I'm not certain if your IAC itself is defective, or if something else is sending it a signal causing it to open up that high. If I remember, the IAC was about $75.00. Not expensive if that is the fix, but very expensive if it doesn't fix your problem.

 

[ExplorerDMB]

At first i thought it was a sticky throttle body, but i've popped the hood when it's revving high and determined that it is fully closed.

A Throttle body is actually never "fully closed". If it was fully closed, then you wouldn't have an air/fuel mixture. The TPS should sit around .92-.99 and it should only be open a hair (looks like it could be "fully closed", but it's not). I'm sure you meant that it wasn't like "stuck open" -- but I just wanted to clarify for others who might read this down the road. Let us know what fixes it!

-Drew

 

[monkeydude3]

well, my buddy had a slightly older explorer but it did the same exact thing, he put a new TPS On and it went away for good. yours could be sticking.

 

[gijoecam]

I just experienced the exact same symptoms last week, but it was due to an overheat condition caused by the thermostat not fully opening. It's possible that the PCM is picking up excessive head temps due to a head temp sensor fault, but I'm not sure if the 4.0 SOHC is equipped with such a sensor or not. It would start to shift funny (like it was short-shifting), idle high, and take a long time to return to idle when revved, and it would do so long before the temp guage moved up near the red area. It would start doing it at about the halfway to 2/3 point in the normal range.

Maybe? I dunno?!

-Joe

 

[BuffaloXplorer]

A Throttle body is actually never "fully closed"....I'm sure you meant that it wasn't like "stuck open" -- but I just wanted to clarify for others who might read this down the road. Let us know what fixes it!

-Drew

Yup, i knew that - thanks for the clarification.

I've cleaned the IAC to no avail. Anyone have a haynes manual around - i seem to have misplaced mine? I need to know if they have an electrical testing protocol for the IAC.

 

[TPLYNCH]

Check and make sure your gas pedal isn't sticking and not releasing all the way....

 

[therise21]

gijoe i think you solved my problem.

 

[gijoecam]

gijoe i think you solved my problem.

For real? dang.... it was dumb luck on my part..... I'm not smart, just a resourceful idiot.

Glad I could help!

-Joe

 

[BuffaloXplorer]

Check and make sure your gas pedal isn't sticking and not releasing all the way....

Pretty sure that's not the case - if it was the throttle plate would be partially open, which it is not. Thanks, though...

 

[hamper19]

I just experienced the exact same symptoms last week, but it was due to an overheat condition caused by the thermostat not fully opening. It's possible that the PCM is picking up excessive head temps due to a head temp sensor fault, but I'm not sure if the 4.0 SOHC is equipped with such a sensor or not. It would start to shift funny (like it was short-shifting), idle high, and take a long time to return to idle when revved, and it would do so long before the temp guage moved up near the red area. It would start doing it at about the halfway to 2/3 point in the normal range.

Maybe? I dunno?!

-Joe

How do you check if the thermostat is not fully opening. I am having something similar, temp guage is hitting the red now, idling high, and as I am braking it surges at around 17mph.

 

[BuffaloXplorer]

If the temp gauge is redlining, you need to change the t-stat regardless. It's a fairly easy, but messy, job and the part is around $10 (for a decent one).

A sticky t-stat will affect your mpg, too, as the truck believes it's in "cold mode" and enriches the fuel to compensate.

 

[IAmTodd]

If the temp gauge is redlining, you need to change the t-stat regardless. It's a fairly easy, but messy, job and the part is around $10 (for a decent one).

A sticky t-stat will affect your mpg, too, as the truck believes it's in "cold mode" and enriches the fuel to compensate.

I believe al had this problem before, it wasn't fully opening and would run the engine faster to cool it. This could be also why you get bad gas mileage. Give it a try, its only a few bucks.