Topic: 2000 RPM at start up

[k]

Out of the blue during a good cold snap, my Jeep started jumping up to 2000 rpm at start up when cold.  As soon as it gets going, it will slow back down, and run fine once warm, and even crank back up normally if it hasen't cooled down enough.   No modifications have been made recently enough to be the cause (I think), and we have already been this cold several times this year with no problems.  Checked for vacuum leak by spraying around hoses and connections already.  Any input is welcome.  Thanks.

[sharpxmen]

Out of the blue during a good cold snap, my Jeep started jumping up to 2000 rpm at start up when cold.  As soon as it gets going, it will slow back down, and run fine once warm, and even crank back up normally if it hasen't cooled down enough.   No modifications have been made recently enough to be the cause (I think), and we have already been this cold several times this year with no problems.  Checked for vacuum leak by spraying around hoses and connections already.  Any input is welcome.  Thanks.

it's by design, should idle around 1500 when cold (so 2000 is not that far off), maybe would go there if it's really cold. if it goes back to normal idle once it warms up then i'd say it is just the way is supposed to work.

[k]

it's by design, should idle around 1500 when cold (so 2000 is not that far off), maybe would go there if it's really cold. if it goes back to normal idle once it warms up then i'd say it is just the way is supposed to work.

It is garage kept (no top), so I wouldn't think it would get that cold, and it didn't do that when it was kept under a car port.  I am trying to remember if I changed the sensor on the throttle body when I swapped those out or not.  I know I did change out the TPS.  Could be the one that came from the scrap yard was bad?  Find out later tonight.

[sharpxmen]

the TPS apparently is the same (although i had different p/n on the 4.0 and the 2.5 i verified later and i remember they are the same), the IAC valve and body/housing are different, make sure you swap both.

[k]

the TPS apparently is the same (although i had different p/n on the 4.0 and the 2.5 i verified later and i remember they are the same), the IAC valve and body/housing are different, make sure you swap both.

yea, found that out the hard way!  And I don't have tamper proof torx bits yet.   Funny thing though, I tried starting it without the IAC valve plugged in and it started normally.  Going to let it get cold tonight and try it again tommorrow.  I did clean the sensor, as it appeared to have some build up on it.  Don't know if that will make a difference, but I am relatively certain that it is going to be related to that sensor at this point.

[sharpxmen]

yea, found that out the hard way!  And I don't have tamper proof torx bits yet.   Funny thing though, I tried starting it without the IAC valve plugged in and it started normally.  Going to let it get cold tonight and try it again tommorrow.  I did clean the sensor, as it appeared to have some build up on it.  Don't know if that will make a difference, but I am relatively certain that it is going to be related to that sensor at this point.

you need to swap the IAC housing and valve, there's no way around it, will return to idle lot slower than normal with the 4.0L on. go get yourself a kit of tamper proof torx bits, they're like $10 (just the bits)

[k]

Might have been some build up around the sensor or housing.  Sprayed both down with some brake cleaner, let dry overnight, and realized I lost the O Ring!  Replaced it with the O ring from the other sensor this morning and reassembled everything.  Worked fine.  Went back to normal start up RPM. (Still going to use this as a good excuss to get those bits! )

[aparke4]

I have an 01 and when cold I will crank it and it will sit around 1500-1700 and eventually come back down upon reaching operating temperature

 have always believed that cars like our bodies need an adequate warm up time ... I will let it run for 4 to 5 minutes until it is over 150 + ... that way I know the internals/ bearings/ motor etc. is warmed up and fluids are flowing like they are supposed to

[dwtaylorpdx]

FYI, if you have a small pin punch once you get the TB off, you can
smack each of the security pins with a hammer and snap them off.
Then a regular torx bit works... At least it worked for me!

Dave