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Idle out of control

Raw16057

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I bought my son a 95 ranger with a 3.0 auto. I put a crank position sensor on it just to get it running then drove it 100 miles home . Since then it idles at 2 to 2 1\2 grand. I have used almost a can of brake clean looking for vacuum leaks , none. I cleaned the IAC and the MAF and made no difference. It will start and run without the MAF plugged in . I am lost maybe the computer took a crap I don't know what else to do . HELP
 


RonD

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After engine is warmed up and idling, unplug the 2 wire connector on IAC(idle air control) Valve
IAC Valve will close and RPMs should drop to 500, or engine may even stall, either is good, it means no vacuum leaks.
But if idle was 2,000rpm after warm up and dropped to 500 after unplugging IAC Valve that would mean computer was setting the high idle with IAC Valve.

If Idle doesn't change then IAC Valve didn't close(move) or it was already closed and you have vacuum leak or someone has messed with anti-diesel screw.
On the throttle linkage you will see an anti-diesel screw, looks like idle screw but we all know you can NOT use an idle screw with fuel injection, no Jets :)
Someone may have adjusted this screw thinking it was an idle screw
So with warm engine idling and IAC Valve unplugged, turn this screw to see if idle goes down, if so keep turning it until idle is at 500.
If RPMs don't change then leave screw as it was, turn it back.

With IAC Valve still unplugged and idle still high, start pulling off vacuum hoses on the upper intake, and cover port with your finger, start with Power Brake booster and PCV Valve hose.
Then move on to smaller hoses
Replace each hose after testing
If RPMs drop you found a leak

Engine off
If you have Cruise Control unhook that cable to see if it is holding open throttle plate
Also the gas pedal cable, it could be holding open the throttle
Remove air tube on upper intake and inspect throttle plate and linkage, make sure plate is not loose and spring is strong enough to close throttle against air flow
 
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cbxer55

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As for the "idle adjustment screw", mine was messed with before I bought it. And it was only four years old at that time. Not knowing for sure how to set it, I just have mine set so that when the throttle is closed, a piece of paper can move freely between the throttle arm and the screw. Been that way for a lot of years and caused no troubles.

On mine, pulling the IAC connector causes the engine to idle down to where it's barely hanging on. For me anyways, cleaning an IAC has never done anything. It is essentially a 12 volt electric motor that fuctuates a diaphragm to control air flow. I believe the motor gets weak and causes issues that cleaning will not fix. I've replaced mine with El Cheapo made in Mexico parts from Vato Zone more times than I can remember. They go bad fast. Three years ago I traded it up for their premium Made in Japan Hitachi IAC. Haven't had another problem with the IAC since.

YMMV!
 
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rusty ol ranger

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I bought my son a 95 ranger with a 3.0 auto. I put a crank position sensor on it just to get it running then drove it 100 miles home . Since then it idles at 2 to 2 1\2 grand. I have used almost a can of brake clean looking for vacuum leaks , none. I cleaned the IAC and the MAF and made no difference. It will start and run without the MAF plugged in . I am lost maybe the computer took a crap I don't know what else to do . HELP
Not to sound insultive with something so simple, but my 97 460 was doing this to. Turned out the throttle was sticking a bit, just something to check. I always start with simple.

Could *possibly* be a bad TPS as well.
 

cbxer55

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In any event, if the "idle screw" is used to raise the idle too high, the PCM will throw a code about something related to the TPS being out of sync with the throttle. Something like that. Had it happen once when I was toying with it. Don't recall the number or exact wording. I was turning it half a turn at a time over several days, just experimenting. Then one day, the check engine light pops on. I read the code, look it up and bingo, I turned it too far. :icon_rofl:
 

rusty ol ranger

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In any event, if the "idle screw" is used to raise the idle too high, the PCM will throw a code about something related to the TPS being out of sync with the throttle. Something like that. Had it happen once when I was toying with it. Don't recall the number or exact wording. I was turning it half a turn at a time over several days, just experimenting. Then one day, the check engine light pops on. I read the code, look it up and bingo, I turned it too far. :icon_rofl:
Shouldnt really need to mess with that screw under normal circumstances. The idle is fully controlled with the IAC, TPS and whatever else.
 

cbxer55

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Shouldnt really need to mess with that screw under normal circumstances. The idle is fully controlled with the IAC, TPS and whatever else.
I know this, but you can make it idle higher if desired. Just can't go lower than what's programmed into the PCM. There have been times in the past, when for reasons unknown to me, it seemed to be idling lower than I liked. Usually ended up being the IAC in the end. Until I put that Hitachi IAC in, mine has had an unusual appetite for IAC's.

TPS doesn't control the idle, it just tells the computer where the throttle is at. Which is why you get a check engine light if you turn the idle up too high. Nothing a small piece of black tape can't fix.:D
 

rusty ol ranger

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I know this, but you can make it idle higher if desired. Just can't go lower than what's programmed into the PCM. There have been times in the past, when for reasons unknown to me, it seemed to be idling lower than I liked. Usually ended up being the IAC in the end. Until I put that Hitachi IAC in, mine has had an unusual appetite for IAC's.

TPS doesn't control the idle, it just tells the computer where the throttle is at. Which is why you get a check engine light if you turn the idle up too high. Nothing a small piece of black tape can't fix.:D
Im not super fluent in EFI. Anything ive had with EFI generally heads to the shop if its related to the EFI. However, i fear no carb, and am espicially fond of the 2150 motorcraft.

Im learning slowly. I guess since its been here for ~32 years, its not going anywhere
 

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