high idle before and after engine swap


Angie

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Background: Purchased a 92 4x4 that was ran hard then parked for a year. It was cheap as it needed new brakes, 7 U-joints, and had a serious miss in the engine. dented drivers front 1/4. still needs work but fixed all that.

Engine: fixed by pulling it out (260,000 kms) and replaced with 1 from our running 94 Explorer (screwed trans) and time to move on from it. Under 180,000 kms on this engine. very clean and strong runner.

Problem: the old engine had a high idle at 1000 RPM. no vacuum leaks. I chalked it up to the badly missing engine and didn't concern myself with it knowing I would be swapping it out anyway.

Now after the swap. Swapped out all the components that were on the running engine from explorer. did not remove anything. out with old, in with new. however the high idle is still there, been driving 2 weeks now after the swap. Swapped the ecm today from a good condition parts truck thinking maybe there was something wrong there. didn't change anything.

What could it be that is giving high idle? Only thing I changed was I deleted the air-con, and deleted the egr BS that went to the exhaust manifold that was in the explorer, used a good intake from another good engine i had sitting in a parts truck.

Checked for a vacuum leak in the booster. all ok there, no vacuum leaks anywhere in the engine bay.

is there a wire harness sensor that i need to look at?

thanks for reading.
 


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Dirtman

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I would do one more engine swap just to be sure.
 

alwaysFlOoReD

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Check the iac.
Check throttle blade closes fully.
Check air intake tube for unmetered air.
Check the PVC tube to air intake isn't leaking or cracked.
 

Angie

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hi floored,

iac came from donor engine worked perfect in exp,
throttle blade, see above^^^^^^ came from intake from good engine parts truck
air intake tube? as in after MAF? swapped with donor.
PVC new, rubber is ok by inspection....

this is why i have my head scratching.... something not adding up.

cheers
 

Dirtman

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You said you deleted the AC. Did you remove the controls as well? When the AC compressor is engaged the PCM turns up the idle RPM. Just because you removed the compressor doesn't mean the computer knows this. It may still be trying to boost the rpms even though nothing is there.
 

alwaysFlOoReD

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What about the ect?
 

Angie

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The controls in cab still same. my guess unless the button is pushed in it should be turned off and doing nothing. (can check for shorts i guess) deleted all ac stuff. the lines, cooler, condenser, swapped the heater box with non ac 1.

cheers
 

Angie

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ECT from new engine.... all engine stuff was not left in the swap. all from other good running engine (s)
 

Dirtman

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I dont have a wiring diagram for that year but there should be a "signal" wire that does nothing but tell the PCM that the hvac controls are in a position that will engage the AC compressor. (This includes heat settings)

If you can find the wiring diagram, find that wire and make sure it's not hooked up or plugged in to anything.
 

Angie

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i have a couple wire diagrams in books... will check that out thanks dirtman. it does make sence though, cheers
 

Angie

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was reading last night on an older thread, someone had same problem. the fix was a sticky throttle cable (cruise cable) and after a different 1 was placed in there it relieved the situation. will try this first before i get out the wire cutters.

cheers
 

Angie

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not the throttle cables, dawned on me, all i need to do to test them is to take them off and no pressure would drop the RPM.... didn't change a thing. didn't look into the ac stuff yet.

cheers
 

Angie

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There is 1 thing that i have been wondering about. the transmission is shifting a bit rough between 1-2 and 3-4. from what i can guess, the 2 switching solenoids in the trans should be replaced. need to do the trans oil and filter anyway. just wondering if these solenoids could have affects on idle speeds? for just monitoring, added a vacuum gauge into the intake and have the rubber hose through the firewall and stuck the hand held style gauge into the ashtray by drilling a hole into bottom and ran hose into that. from watching it, idles at 25, (a bit high) with great movements through all ranges. zero needle movements at idle, so guessing no stuck valves or other internal issues.

cheers
 

Angie

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UPDATE:

When i had the engine out and the wire harness (original) out I tore open all the looms and traced all the wires looking for any frayed/chewed wires that could have caused the miss (IE injector wire broke) etc, there were no broken connections or missing bits. Re-loomed the harness and taped up neat. Hence why scratching head as to what I was missing in the swap with same problem.

Friend came over this morning and we were looking it over and he unplugged the wires connecting the plug for the IAC, nothing happened. the idle stayed the same 1100 rpm or so on a warm engine. I am wondering if this should have made any changes in the rpm with that plug connected or not connected? how many volts should i be getting on those 2 wires hot and cold? and if i follow those 2 wires back to the wire harness, what will they be plugged into and how to trouble shoot the wires?

cheers
 

alwaysFlOoReD

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Unplugging the iac should have brought idle to 500 or less or stall out.
Not sure on voltages.
 


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