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4.0 ohv rough idle runs rich codes ect code i forgot 159koeo/r, 412koer 129koer


blue_pill85

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so in my weeks of searching ive seen this issue or similar a million times however i have yet to see it solved.hopefully we can so lets go back to the beginning. i bought a 94 ranger 4x4 4.0 ohv auto trans about a year ago. ran rough when i got it. plugs and wires junkyard maf did the trick til recently. all of a sudden at a stop light it started surging and bucking almost died idle drops to 500 rpm (where it has been since) put in neutral and gave it about 1500 rpm for a sec. now it idles rough in park. in gear it surges and bucks. finally figured out how to check my codea and that they were 3 digit. refer to the title. checked maf voltage a- battery neg gave battery voltage, batt pos to b gave battery voltage, c to bat neg 5.9 volts, i honestly dont remember doing d offhand but i did. replaced ect new part, helped a bit for 2 days, replaced maf with parts store brand spanking new for 100 (unplugged battery connected terminal, swapped out maf, connected battery) still runs like poop throws identical codes (returned maf not made of money), checked voltage to tps 1.09 at idle, checked resistance on iat sensor to chart got resitance that made sense... idr exactly but close per chart not -4000*, played with and cleaned maf connector got iirc .9volts signal at idle, pulled all plugs (motorcraft oem as i had found recommended lurking trs) all equally covered in dry black carbon cleabed them with electrical parta clraner i had on hand) replaced wires again had a buddy verify i put them on rught for sanity check. that brings us to today. pulled the plug off the iac valve falls dead on its face. cleaned iac with throttle body cleaner (not as well as i wouldve liked but only had a small about in the can) just to see what it does cuz im a curious sort i loosened the iac while it was running. with a little air gap idles great. cleaned iac pintle(sp?) moves freely reinstalled runs like crap. (damn did not unplug battery will do later) anyways also the clear flooded engine test. after idling for a bit. key on pedal down vroom fires right up and revs. wtf right? so sanity check i rev it up to maybe 3500. shut it off foot on the pedal still. try clear flooded again key on pedal down cranks for days. so obviously shes holding some fuel at idle? repeated both tests with same results.

came inside to start writing my experiences down hopefully with some help we can figure it out and get a solution poated so the next poor bastard doesnt have to blow a bunch of money and time chasing these gremlins. i have not replaced iac yet but i think thats.my next step anybody have any comments? im doing all this from youtube and trs lurking.

also sorry if.my post is hard to decipher... if it is.lets work it out like i said save the next schlub some headache this seems to be super common. ill try to get some videos on this thread as well

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blue_pill85

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no egr or dpfe to my knowledge on this engine aluminum intake

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blue_pill85

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also sprayed every vac line and intake hose i could with tb cleaner no changes in idle

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RonD

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All fuel injection computers have a Clear Flooded Engine routine

Key on engine off
Press gas pedal down to the floor and hold it down
If computer sees 0 RPMs and WOT(wide open throttle) it will shut off Fuel Injector pulses but leave spark on

Now try to start engine, still holding gas pedal down to the floor
It should NOT start, it should NOT fire at all, no fuel
If it fires then there is fuel getting into intake

If RPMs get to 400 computer will turn on fuel injectors, if you release gas pedal computer will turn on injectors.

Common issue on older Return Fuel systems, 1997 and older Rangers, was a leaking Fuel Pressure Regulator(FPR)
FPR on the 4.0l will be behind alternator on lower intake, it will have the Fuel Return hose and a smaller Vacuum hose attached
Remove this vacuum hose and check it for gasoline, if FPR leaks then extra fuel will be sucked into the intake, via this vacuum line, causing flooded condition
 

blue_pill85

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did that. as long as i gas it before i shut it off and hold it down it will turn over and no start... if i let it idle and flood it will fire up. fpr holds vacuum and no fuel in line.



UPDATE. otw to work after cleaning and otherwise wiggleing parts in ny iac i now lean out. unplugged my iac and can get min idle. looking more and more to me like an iac solenoid issue or ias sticking . maybe on break ill replace it. i think its reasonably cost effective. back to school is killing ny wallet. maybe do some videos as well.

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blue_pill85

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just occured to me a sympton i forgot about. a few months ago i had a severely high idle. i attriduted to stuck thrittle pulley ( name evades me) i took all the plastic covering off it and lubed and wiggled. and it dropped back down.... now im thinking this could have been the iac sticking and let go in the course of setting tools on it and such.

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Vincenthdfan

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My 93 4.0 was drivin me nuts doing similar issues as yours...idle all over the place.

I bought an aftermarket IAC, ran worse, tested TPS, tested good...

I put the original FOMOCO IAC back on, installed a new TPS and it idles and runs great again.

I also installed a new fuel filter and it cured some intermittent stalling/bucking issues.

Also, check your intake hose/duct work for dry rot/cracking underneath around the MAF end....I found (and sealed) several cracks in mine on that end.
 

blue_pill85

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ahhh the saga continues. running LEAN all day died on me otw home from work cleared codes from screwing with it earlier. now im getting 157, 158, 159 koeo/m heres the kicker. will not let me run engine running diagnostic. wire in fire it up doed not do id blink or single blink for goose test. does rapid blinks then immediately fires off with 998 koeo test not passed..... also newly noticed when the fuel pump kicks on durine koeo test sounds like its blowing bubbles. when it died i did double check tps was connected because it is running just like it did when i disconnected. that is to say instantly leans out. guess ill try popping in a tps.

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