High Idle

[budro]

I have a 93 Ford Ranger with a 4.0. It continually wants to idle at about 1100rpm. We have checked all the vacuum lines off the tree at the back of the intake manifold. New AIC valve, transmission vacuum modulator, fuel pump, fuel pressure regulator, new fuel filter, replaced vacuum line to fuel pressure regulator. No codes show up on the computer besides the 111 which is all clear. Have not adjusted the idle screw. This isn't really a problem driving normally but when you want to stop on snow or ice and the truck is still trying to push you forward it gets scarry. Anybody have any other ideas of what to look for?

 

[baddis]

can you pull on the throttle cable to get the idle down?maybe the cable isn't returning all the way

 

[budro]

Nope there is about a 1/4 inch of slack in it. It is resting fully on the idle stop screw. Which i have never adjusted.

 

[baddis]

have you checked to see if you have an intake gasket leak?

 

[budro]

Whats the best way to test that? Besides spraying carb cleaner around the edges of the intake? Thats kindof scary on a hot motor especially here its been between 90 and 100 degrees.

 

[baddis]

might be able to block off the tb and see if it stays running.

 

[budro]

One other thing to mention is that I unplugged the IAC while the motor was running and it had no effect what so ever to the idle.

 

[baddis]

i am not as up to date on the 4.0 since i have never had one .but seeing that you have no codes i would say it would be more a mechanical problem than an electrical one.

 

[MAKG]

i am not as up to date on the 4.0 since i have never had one .but seeing that you have no codes i would say it would be more a mechanical problem than an electrical one.

That's false on ANY OBD-I computer. They aren't completely infalliable. Not by a longshot.

And there are three self tests. Only one result was posted. Run the other two.

The obvious problem is a vacuum leak. MEASURE the vacuum; leaks don't have to come from obviously broken lines.

 

[budro]

What are the other 2 tests for the computer?

I know about the posibility of where vacuum leaks are. I was just hoping to find something without pulling the intake off and it not fixing the leak.

 

[MAKG]

There is an engine-running and a "Continous" test.

For external vacuum leaks, you can spray brake cleaner around the visible joints while idling and see if the idle goes up. For vacuum components, you can suck on them with a hand vacuum pump to make sure they hold vacuum. Don't forget the charcoal cannister line. Replace the PCV valve out of hand (if it's stuck, it can bypass the throttle). If EVERYTHING else checks out and you still have low vacuum, replace the lower intake manifold gasket. Note that blown gaskets will usually foul at least one spark plug with oil and/or coolant, and may get coolant into the crankcase.

Do you know you have a vacuum leak? What are the results of the vacuum test?

 

[racsan]

i had a problem with high idle that ended up being a failed gasket between the fuel rail and lower intake manifold. the only way i found it was by tearing it down, at the front and back it had "pulled in" my idle was so high, that spraying with carb cleaner didnt do a thing. its worth checking out first before messing with sensors, about 60-70 in gaskets (i replaced my valve cover gaskets due to a leak i had anyhow, i also pulled the lower intake to be sure i was o.k. there.) vs 300+ for all the various sensors. paying for a diagnostic test would be worth it in this case, i went the wrong road first, but i have all the original sensors if i ever actually need one.
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indica strains

 

[96xltV6]

im sick of spending money on trying to fix my ranger..it has a hissing and high idle now too

 

[crazywhiteboy]

im getting kind of the same thing. i was climbing an ice/snow hill spinning all four at about 4500. wen i got to the top i pulled aside shut off my truck but it tried to stay alive. then the rpm's went through the roof but my ignition was off. it took probably 3 seconds for me to jump out, open the hood and yank the power cable off the battery. then it shut off. i let it sit for about 5 mins then started it back up. the rpm's went to 3000 and stayed there for the ride home. it didn't get hot though. i was thinking either elec got wet or vacuum lines. but my engine light didnt come on once during the whole scenario. any help would be greatly appreciated. thanks!

 

[reno]

Take a spray bottle of water, and spray the vacuum lines and intake a little at a time on the intake and you will safely find the trouble spot.