Rev hang issue

[CheepComanche]

For the past few months my Renix 2.5 Comanche has had a rev hang like issue. When I take my foot off the throttle to shift, the rpm doesn't go down and in some cases it goes up. Originally I thought my o2 sensor was to blame but after replacing that with an NTK sensor the problem didn't resolve. I've now moved on the the TPS however I am unable to backprobe the connector as I can't fit the probes of my multimeter in the plug. I'm not sure where to go from here. 

[eaglescout526]

TPS is pretty easy to back probe. Your probes don’t have the cones on them do they? If you use the probes and just follow the wire into the protective boot of the weather pack, it will go right in and give you a reading. 
 

Now high idle on a 2.5L would lead me to a vac issue first. I used to have such on occasion where the hose from the bottom of the manifold would come off and create a high idle for me like 1100-1300. The hose in question would go to the back portion on top of the valve cover. 

[CheepComanche]

Yeah, I have the cones off the the probes but still not luck getting the probes into the plug. It looks the the plastic of the plug is tight around the wire.

[eaglescout526]

Well don’t be afraid to really jam the probes in there. 
 

Hell unplug it and then jam the probes in and then plug it back in 

[CheepComanche]

Alright, will do. Also, was vacuum line that you mentioned the pcv hose? 

[eaglescout526]

It is a PCV. The front most hose goes to the air box, the rear goes to the base of the throttle body. If the original hose is still there at the base of the TB, I would bet its slipping off and needs to be replaced or just zip tied on.

[cruiser54]

AND, make sure your intake manifold bolts haven't loosened up!!

[CheepComanche]

I've put a hose clamp on the pcv hose and the throttle body bolts are tight. I'm wondering if it could be a bad map sensor or a vacuum leak somewhere else. I have noticed that It rev hangs worse going up a hill. 

[eaglescout526]

You can always unplug the hose to the MAP sensor and see if it changes. 

[CheepComanche]

I unplugged the map sensor vacuum hose and the truck just ran rough. I also unplugged the tps and it also just made the truck run rough. This leads me to believe that both sensors are working so I’m not sure where to go from here. 

[cruiser54]

Intake manifold bolts and hoses? 

[CheepComanche]

The bolts are tight. Maybe I should replace all the vacuum lines as they are all original.

[Ωhm]

Make sure linkage between pedal and TB is free from kinks/binds and is well lube.

[CheepComanche]

The throttle snaps right back but I have noticed the rev hang gets worse as the truck warms up. Not sure what that could mean 

[eaglescout526]

Vac leak or the ISA is sticking. 

[Ωhm]

Bad motor mounts can hang up the linkage.

[CheepComanche]

The motor mounts could certainly could be my problem. The engine in my jeep was swapped in a little over a year ago and I’m not sure if the mounts are bad. I’m not sure how much the engine should move when you rev it. 

[CheepComanche]

I know this is a little off topic but I was wondering what this is for. Some of the vacuum lines going into it fell off when I messed with it and others I can’t remove.

[eaglescout526]

That’s just the harness. Believe it or not the 4.0L uses the same harness style, so if you want to replace the harness itself, you can get the 4.0 one but you’ll have to trim the bigger lines and get some flexible vac line to make the connections. But the hoses are glued in. 

[CheepComanche]

I'm considering deleting the egr valve and removing as many vacuum lines are possible. I'm not sure what goes into this process and what vacuum lines can be deleted but I would like to clean up the engine bay. 

[eaglescout526]

You can delete maybe one or two lines but most are pretty essential to the proper operation. 

[CheepComanche]

When it comes to an egr delete, what all is required?

[CheepComanche]

After messing with the jeep quite a bit I thought my rev hang was being caused by the isa. I rebuilt it, however no change. I also drove the jeep without the isa which completely resolved the rev hang. Just to make sure, I bought a new isa but still no change. This really confuses me because I know I have a properly working isa but if I remove it my problem goes away. 

[eaglescout526]

ISA adjusted properly though?

[CheepComanche]

Yes, I adjusted it so when its fully extended the engine revs to 3500