Yet another 4.0 Idle issue

[91rangeryder]

Hi TRS members I've got an idle and overall performance issue with my truck I've searched threads and have found similar problems but none of their fixes helped me. Truck starts runs decent but at operating temperature it Idles at around 1100 to 1200 in park and no less than 1000 in drive when you rev the motor let’s say to3k it doesn’t idle down right away it will drop to 2.5k then 1.5 then about 1.2 in about 3 to 5 second increments. When driving it the motor seems hesitant throughout the throttle range. This is my first 4.0 and fith ranger and it seems as slow as some 2.3s and 3.0s I've had

Parts replaced/checked in order of test or replacement
O2 sensors: replaced both due to failed emissions test. after replacement passed retest with flying colors
EGR checked and is functioning
Checked for vacuum leaks everywhere
Cleaned MAF with sensor safe cleaner
IAC checked operation valve is working properly
TPS replaced/ with a new unit "replaced because had a spare new one"
Replaced All intake & exhaust manifold gaskets including upper and lower fuel rail and valve covers

Any Ideas or suggestions would be very appreciative or if I missed a post covering this let me know thanks !

 

[91rangeryder]

Update

After racking my brain and being convinced this is a TPS issue I started to fiddle around with the sensor after taking it off running the motor then unplugging it running the motor putting the old unit on running it I didnt fix the issue until.... I left the new replacement TPS on the motor and plugged the old one into the connector. After I did this the truck idled at about 850 and when I reved the motor up it dropped promptly back to idle. I don't know why this fixed my issue am I missing something here ? any theories guys ?

 

[GoGoggansGo]

Hi TRS members I've got an idle and overall performance issue with my truck I've searched threads and have found similar problems but none of their fixes helped me. Truck starts runs decent but at operating temperature it Idles at around 1100 to 1200 in park and no less than 1000 in drive when you rev the motor let’s say to3k it doesn’t idle down right away it will drop to 2.5k then 1.5 then about 1.2 in about 3 to 5 second increments. When driving it the motor seems hesitant throughout the throttle range. This is my first 4.0 and fith ranger and it seems as slow as some 2.3s and 3.0s I've had

Parts replaced/checked in order of test or replacement
O2 sensors: replaced both due to failed emissions test. after replacement passed retest with flying colors
EGR checked and is functioning
Checked for vacuum leaks everywhere
Cleaned MAF with sensor safe cleaner
IAC checked operation valve is working properly
TPS replaced/ with a new unit "replaced because had a spare new one"
Replaced All intake & exhaust manifold gaskets including upper and lower fuel rail and valve covers

Any Ideas or suggestions would be very appreciative or if I missed a post covering this let me know thanks !

Had a simliar issue with my 93 4.0 it had a check engine light, and would run rough and sometimes misfire. Needless to say after having my dads master tech buddy looked at it he cleans the MAF to almost new, and still cant get ride of the cel, and recommends that it is the MAF. So I went out and bought a brand new one at advance BWD lifetime warrenty the lot. Solved all of my issues, and the truck seems to have better performance even when compared to when I did not have the cel light just a thought

 

[91rangeryder]

Thanks for the info Go. I'll look into the MAF a little more. I really hope it's not that. Don't want to drop 2 bills on one. I have no CEL but who knows I'm stumped at this point.

 

[GoGoggansGo]

Thanks for the info Go. I'll look into the MAF a little more. I really hope it's not that. Don't want to drop 2 bills on one. I have no CEL but who knows I'm stumped at this point.

60 bucks

 

[daniel3507]

I replaced my MAF with Ford (afraid of using anything other than factory parts for something like that) and it helped out my truck a lot. Have you replaced the fuel filter? Might be gummed up making it not flow very well. Cheap and easy maintenance that never hurts.

 

[GoGoggansGo]

I replaced my MAF with Ford (afraid of using anything other than factory parts for something like that) and it helped out my truck a lot. Have you replaced the fuel filter? Might be gummed up making it not flow very well. Cheap and easy maintenance that never hurts.

Sorry for taking so long but yes try that and some seafoam

 

[91rangeryder]

Yes I did the fuel filter when I first bought the truck maybe 3k miles ago forgot to mention that . I've used seafoam on other vehicles but didn't notice much. It smoothed out the idle a bit on a 4.0 Cherokee of mine. On the ranger 4.0 ohv do you suck the seafoam up with the brake booster vacuum line ? That’s what I did on my old jeep.

 

[91rangeryder]

Anyone know of the symptoms of a bad coolant temp sensor.Not the one for the gage on the dash but the one that feeds motor temp info to the computer. Thiis is my next area of exploration. I'm thinking if this is sending a cold reading to my computer while the engine is at operating temp it could be causing my idle issue. Someone stop chime in if I'm way off. Thanks

 

[daniel3507]

Not sure on the sensor but with the seafoam just pour a little in the vacuum line from the brake booster and some in the fuel tank. I think it says a third for each on the can.

Sent from my LS670 using Tapatalk 2