Topic: Post-4.0L TB Swap ... High Idle

[Sine Deviance]

Monday I swapped in the 4.0L TB. I reused the sensors from the 2.5L TB like I was supposed to. After swapping I've noticed that my idle is higher than it was before (it now idles at 1000-1100 RPM, unless I have the heater blower and headlights on, then it idles around 900.) Also, when I'm driving and I come to a stop, as the engine idles down it will hang around 1500 RPM for a few seconds and then slowly idle down to 1000 RPM. At first I figured the ECU just needed time to sort itself out so I didn't think much of it, but it's been five days now and I've put at least 500 miles on the Jeep since Monday. It's still doing it.

Anybody know why this is happening?

[93yjFirstJeep]

ur jeep learns after 50 warm up cycles have been completed. I just swapped my tb a few weeks ago and it still does that, but not as bad. It gets better over time.

[sharpxmen]

Monday I swapped in the 4.0L TB. I reused the sensors from the 2.5L TB like I was supposed to. After swapping I've noticed that my idle is higher than it was before (it now idles at 1000-1100 RPM, unless I have the heater blower and headlights on, then it idles around 900.) Also, when I'm driving and I come to a stop, as the engine idles down it will hang around 1500 RPM for a few seconds and then slowly idle down to 1000 RPM. At first I figured the ECU just needed time to sort itself out so I didn't think much of it, but it's been five days now and I've put at least 500 miles on the Jeep since Monday. It's still doing it.

Anybody know why this is happening?

IAC valve and housing needs to also be swapped (in case you didn't do it) - if you did then the high idle is due to a vac leak, either you have a vac line unplugged or cracked or your new t/b does not seal properly onto the intake manifold

[Sine Deviance]

ur jeep learns after 50 warm up cycles have been completed. I just swapped my tb a few weeks ago and it still does that, but not as bad. It gets better over time.

IAC valve and housing needs to also be swapped (in case you didn't do it) - if you did then the high idle is due to a vac leak, either you have a vac line unplugged or cracked or your new t/b does not seal properly onto the intake manifold

Okay, I'll keep this stuff in mind. I know it's not a vac leak because all the vac lines are good and hooked up. I know the TB is seated and sealed properly, I used a new gasket and took special care to line it up right. I'll check my vac lines again and if that isn't it I'll just wait a while longer and see.

Thanks!

[Bounty Hunter]

Also consider erasing the memory in the ECM by disconnecting the battery and touching the two battery leads together.

[Sine Deviance]

Also consider erasing the memory in the ECM by disconnecting the battery and touching the two battery leads together.

I'll definitely do that tomorrow, thanks :)

[countryboy15]

 I am thinking of swapping to the 4.0 L throttle body. I just want to know did it work, how long did the high idle problem persist, and how did you get rid of the problem. Also does it affect your gas mileage.

[Sine Deviance]

I am thinking of swapping to the 4.0 L throttle body. I just want to know did it work, how long did the high idle problem persist, and how did you get rid of the problem. Also does it affect your gas mileage.

Actually, my high idle problem seemed to be a result of my PCM being damaged, and not the 4.0L throttle body. I recently replaced my PCM and the high idle went away. So mine was certainly a special case, YMMV.

Hypothetically, swapping to a 4.0L throttle body and using a better intake with a better air filter will increase gas mileage because the volumetric efficiency of the engine goes up. But in the real world, you will either see a few mpg or not. It's better to do the swap for better throttle response and a slight gain in power, which you will definitely get.

[Torch_Ind]

I didn't notice much fuel range difference but I don't really monitor it mile for mile. I still burn roughly the same driving it to work and back and around town the same as before. I get about 2 weeks on my tank doing my daily commuting.  when I plow and do extra things and off road I burn more but also did more with it. all in all I never noticed any crazy gains fuel econ wise.

hug improvement in throttle response and higher rpm's range power. 

never had the idle problem