4.0 issues

[Timbit]

truck specs:

92 4.0 4x4 XLT,5 spd....HAD air tilt cruise before a cab swap....electronic 4x4 too although shouldn't make a difference as it has own computer to control....

the engine had 170k miles on it..and the cab was rotten...beyond repair!! So I find a 90 2 wheel x-cab truck and swap the cab....don't want air cause it doesn't work, and same with cruise....so bonus the old truck doesn't have it...I use the heater box on the firewall and the heater controls and take out the CC harness...while doing all this swap, I find the computer has been getting wet, and it rotting it out...I was surprised the truck was even running

so I bolt new cab in with NO a/c controls, and CC harness missing, but wiht the computer I decide I need a new one! so I get a computer from a truck out of town, of course, because NO yard in town had a computer for my truck. so I get one that was made for:

4.0, 4x4, NO air, 5spd...everything should be the same....truck runs great after with all this swap done, and we are ok...well truck breaks tranny, and sits for a year, new house, new garage, get everything going, and I get the truck fixed...and replace lots of stuff to make it new again, and also another engine from a 92 exploder...it has 132k miles on it, still runs great.....brings me to my new problem!!!

I have a high idle that won't go away!!..I have replaced all sensors on engine within two years, Except VRS and idle bypass...mind you, I have 4 other IAB sensors for this engine, and all 4 either make it worse or it stays the same...if I let the engine sit for a long time idling it will do fine..right about 800-850 but will go up and stay about a 1k on my tach and be up while driving around even at idle at a stoplight...also the engine seems to really jump around while driving, when letting off the gas it will start to slow the truck down, but will do it with quite harshness....timing chain maybe???

I have HORRIBLE gas mileage, and I still don't know what would be causing this anyone have any ideas here for me? Like I said, all new sensors except the 2 mentioned and also new plugs, wires, filter, all within the past two years...so, does this computer possible cause a problem? cause it wasn't the original specs? and should I break down and get the new IAB valve?

I am just throwing out all issues I see, and also all specs of truck current and all mods that has been done.....I am getting lost here, and just looking for mostly 2nd opinion answers and brainstorming......

Tim

 

[fireguy12117]

whenever i had IAC (IAB as you called it) i always had problems idling, never at speed. perhaps double check the plug wires to make sure they are in the right order? ive had motors run weird with a messed up firing order, but still drove em till i managed to figure it out. check engine light on? visual inspection on everything, just to make sure you didnt miss a vacuum line or plug someplace since its been over such a long period for the repairs? now that i say that- double check vacuum leaks! they wreak havock...and a buncha other people on here will hopefully chime in with some more ideas....

 

[Timbit]

lol....IAC..that's what I meant to call it..couldn't think off the top of my head about it. Anyway, yeah, no engine light on, so I don't have codes, and visual inspection shows up ok, no vaccuum leaks that I can find...have already checked all those. I am thinking possible intake gasket leaks??? I don't know

 

[Timbit]

hey guys!! haven't been on here for soooo long, glad to see its still going strong I love this site!

anyway, still having this same problem! just haven't really bothered with it as the truck is only an occasional driver, but I am hoping now to turn a nice bronco 2 into a wheelin' vehicle...gonna use this drivetrain to do it, but wanna fix issues....let me just re-iterate:

1. high idle-no codes, nothing shows wrong, I am sure I need to replace the lower intake gasket....have played with the MAF and got a brand new IAC valve...should I get a new MAF???

2. extreme bucking in gear at idle speed, no matter gear-I can drive the truck great at anything over 1500 RPM....if I let it drop below that RPM, while in ANY gear(5spd)then the truck will buck and jump like your hitting the gas and letting off quickly....without even touching the gas pedal!! it is really hard on the truck, and it really confusing me. I have come to think maybe a timing chain problem? or would the high idle be causing this...I tried even a different TB from the old engine and still no change...

just looking for opinions still guys, and thoughts let me know if anything comes to mind..

PS, if anyone has a nice 89 or 90 bronco 2 in decent body shape(drivetrain irrelevant) for sale, close to northern ontario, or northern michigan let me know!

 

[Timbit]

no one????

no opinions on the engine issues experiencing??

 

[AaronC47]

High Idle

Just to throw in my nickels worth here, A friends daughter had an 87 honda accord that idles way high then way low, was very erratic, I couldnt get it to idle to save anyones life. She left for the summer her mom sells car for her,
Now My ex wifes daught has the same year and model and even same color car doing the same damn thing. So I found a downloadable accord manual online, Come to find that someone ran vacuum lines wrong and so the EGR was not operating properly,
Moral of the story try checking vacuum lines no matter how much your sure its right, maybe the guy working on it before you screwed something up.