4.0 ohv idle and running problem

[bigred4x4]

ok so basically this is what happens.i start the mototr the idle is high about 2000 rpm high for a minute then drops way down then bounces between 300 and like 1500 rpm (sometimes itll stall)that s my first problem.next i go to put it in drive and it runs fine when its cold.as it warms alittle bit its starts to miss/rattle and jerk the truck when accelarator is steady.there is no check engine light and no codes.sometimes its worse than others and once it starts doing it it aslso does it in park but not as bad.


ANY IDEAS? iv been trying to figure this out for months


also id like to add that it doesnt kick into idle wen i take my foot of the gas itll just down shift wen my speed decreases (making it harder to stop!!!)


this is what iv done so far
replaced the motor with a 95 4.0 100k miles(ran fine at first except for idle)
replaced coil pack
new plug wires
new plugs
new thermastat
new IAC
new waterpump
recently changed transmission fluid
new radiator/hoses

 

[Dylansav]

this might seem kind of obvious but have you done any of the basic maintenance on it? I see you have already put in a new AIC and plugs but there are some others that could be causing it.

I've had many idle problems with my truck and any of these have cause it for me...

Besides the AIC and plugs you could take a look at the air filter and fuel filter. you could also have clogged fuel injectors or your fuel pump could be going or anything like that. I've also had a clogged up PCV valve be the cause of Idle up into the 2000s before.

I try to narrow it down. You just gotta think it has to do something with either it's not getting the right amount of 1. Air 2. Fuel 3. Spark.

I wish you goodluck! These Ex's like other trucks can be a challenge sometimes but keep with it!

 

[bigred4x4]

the air filter is fine the fuel pump isn't that old at all its been replaced before the PCV is good I checked that.the injectors should be clean if that pour in cleaner really works.the next thing iwas going to do is change the fuel filter but besides that wat other things should I check up on the funny thing is the idle is steady with iac unplugged...? But the idle isn't concerning me as much as all the vibration and jerking going down the road and under accelleration and alittle bit in park or neutralonce the motor warms up.

 

[Four0Sport]

the jerking while driving could be a fuel/air problem. you say when you unplug the IAC the idle returns to normal? hmm.. maybe a faulty IAC. might also want to clean the MAF as this can also cause air/fuel problems and give you symptons like you described.

hope this helps,

Jack

 

[bigred4x4]

Wow I actually fixed my truck thanks guys yall saved me a trip to the dealership i messed around with maf sensor ,the intake ,and one of my plug wires had a tear in it and was touching metal so that cylinder probably wasn't getting the spark it needed and as far as the idle even no its new I think the Iac is faulty it doesn't do anything wen u pull it of the intake and turn the key except make click noise.



Thanks again,