low idle warm 90 jeep 4.0
 

Hi Folks:
I have a '90 Cherokee Laredo injected 4.0. When it's warm, after
I've restarted it, it goes through this phase:

If I let it sit and idle, it will slowly go from say 1,000 RPM to 600
or so, and it will be fine. It I step on the gas at all, even if it's
just pulling away from the gas-station pump, it will drop to almost
stalling speed. Once in a while it does stall. Instead, if I let it
idle for about 2 minutes, this doesn't happen. I've changed the O2
sensor, a few of years ago. I've put about 30k miles on it since.
Could that be bad? The last time it STOPPED doing this was one time I
had the gas-tank down to change the pump, which I've done twice so far.
Maybe it's Jersey Gas. This might be something that clears up when I
disconnect-reconnect the battery. I'll have to try that again. Or,
maybe there's a chip upgrade?
Thanks!
Harry

Re: low idle warm 90 jeep 4.0
 

Your symptoms can be caused by a dirty connection on the TPS. I
recommend spray contact cleaner on them to clean them up. WD40 will
work in a pinch.

Our idle goes something like yours every couple years and the clean
fixes it right up.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

HarryHydro wrote:
>
> Hi Folks:
> I have a '90 Cherokee Laredo injected 4.0. When it's warm, after
> I've restarted it, it goes through this phase:
>
> If I let it sit and idle, it will slowly go from say 1,000 RPM to 600
> or so, and it will be fine. It I step on the gas at all, even if it's
> just pulling away from the gas-station pump, it will drop to almost
> stalling speed. Once in a while it does stall. Instead, if I let it
> idle for about 2 minutes, this doesn't happen. I've changed the O2
> sensor, a few of years ago. I've put about 30k miles on it since.
> Could that be bad? The last time it STOPPED doing this was one time I
> had the gas-tank down to change the pump, which I've done twice so far.
> Maybe it's Jersey Gas. This might be something that clears up when I
> disconnect-reconnect the battery. I'll have to try that again. Or,
> maybe there's a chip upgrade?
> Thanks!
> Harry

Re: low idle warm 90 jeep 4.0
 

Your symptoms can be caused by a dirty connection on the TPS. I
recommend spray contact cleaner on them to clean them up. WD40 will
work in a pinch.

Our idle goes something like yours every couple years and the clean
fixes it right up.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

HarryHydro wrote:
>
> Hi Folks:
> I have a '90 Cherokee Laredo injected 4.0. When it's warm, after
> I've restarted it, it goes through this phase:
>
> If I let it sit and idle, it will slowly go from say 1,000 RPM to 600
> or so, and it will be fine. It I step on the gas at all, even if it's
> just pulling away from the gas-station pump, it will drop to almost
> stalling speed. Once in a while it does stall. Instead, if I let it
> idle for about 2 minutes, this doesn't happen. I've changed the O2
> sensor, a few of years ago. I've put about 30k miles on it since.
> Could that be bad? The last time it STOPPED doing this was one time I
> had the gas-tank down to change the pump, which I've done twice so far.
> Maybe it's Jersey Gas. This might be something that clears up when I
> disconnect-reconnect the battery. I'll have to try that again. Or,
> maybe there's a chip upgrade?
> Thanks!
> Harry

Re: low idle warm 90 jeep 4.0
 

Your symptoms can be caused by a dirty connection on the TPS. I
recommend spray contact cleaner on them to clean them up. WD40 will
work in a pinch.

Our idle goes something like yours every couple years and the clean
fixes it right up.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

HarryHydro wrote:
>
> Hi Folks:
> I have a '90 Cherokee Laredo injected 4.0. When it's warm, after
> I've restarted it, it goes through this phase:
>
> If I let it sit and idle, it will slowly go from say 1,000 RPM to 600
> or so, and it will be fine. It I step on the gas at all, even if it's
> just pulling away from the gas-station pump, it will drop to almost
> stalling speed. Once in a while it does stall. Instead, if I let it
> idle for about 2 minutes, this doesn't happen. I've changed the O2
> sensor, a few of years ago. I've put about 30k miles on it since.
> Could that be bad? The last time it STOPPED doing this was one time I
> had the gas-tank down to change the pump, which I've done twice so far.
> Maybe it's Jersey Gas. This might be something that clears up when I
> disconnect-reconnect the battery. I'll have to try that again. Or,
> maybe there's a chip upgrade?
> Thanks!
> Harry

Re: low idle warm 90 jeep 4.0
 

Your symptoms can be caused by a dirty connection on the TPS. I
recommend spray contact cleaner on them to clean them up. WD40 will
work in a pinch.

Our idle goes something like yours every couple years and the clean
fixes it right up.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

HarryHydro wrote:
>
> Hi Folks:
> I have a '90 Cherokee Laredo injected 4.0. When it's warm, after
> I've restarted it, it goes through this phase:
>
> If I let it sit and idle, it will slowly go from say 1,000 RPM to 600
> or so, and it will be fine. It I step on the gas at all, even if it's
> just pulling away from the gas-station pump, it will drop to almost
> stalling speed. Once in a while it does stall. Instead, if I let it
> idle for about 2 minutes, this doesn't happen. I've changed the O2
> sensor, a few of years ago. I've put about 30k miles on it since.
> Could that be bad? The last time it STOPPED doing this was one time I
> had the gas-tank down to change the pump, which I've done twice so far.
> Maybe it's Jersey Gas. This might be something that clears up when I
> disconnect-reconnect the battery. I'll have to try that again. Or,
> maybe there's a chip upgrade?
> Thanks!
> Harry

Re: low idle warm 90 jeep 4.0
 

Mike Romain did pass the time by typing:
> Your symptoms can be caused by a dirty connection on the TPS. I
> recommend spray contact cleaner on them to clean them up. WD40 will
> work in a pinch.
>
> Our idle goes something like yours every couple years and the clean
> fixes it right up.

That and probably a gummed up/sticky IAC valve or butterfly. Amazing
what a teeny bit of crud in the wrong place can do.

--
DougW

Re: low idle warm 90 jeep 4.0
 

Mike Romain did pass the time by typing:
> Your symptoms can be caused by a dirty connection on the TPS. I
> recommend spray contact cleaner on them to clean them up. WD40 will
> work in a pinch.
>
> Our idle goes something like yours every couple years and the clean
> fixes it right up.

That and probably a gummed up/sticky IAC valve or butterfly. Amazing
what a teeny bit of crud in the wrong place can do.

--
DougW

Re: low idle warm 90 jeep 4.0
 

Mike Romain did pass the time by typing:
> Your symptoms can be caused by a dirty connection on the TPS. I
> recommend spray contact cleaner on them to clean them up. WD40 will
> work in a pinch.
>
> Our idle goes something like yours every couple years and the clean
> fixes it right up.

That and probably a gummed up/sticky IAC valve or butterfly. Amazing
what a teeny bit of crud in the wrong place can do.

--
DougW

Re: low idle warm 90 jeep 4.0
 

Mike Romain did pass the time by typing:
> Your symptoms can be caused by a dirty connection on the TPS. I
> recommend spray contact cleaner on them to clean them up. WD40 will
> work in a pinch.
>
> Our idle goes something like yours every couple years and the clean
> fixes it right up.

That and probably a gummed up/sticky IAC valve or butterfly. Amazing
what a teeny bit of crud in the wrong place can do.

--
DougW

Re: low idle warm 90 jeep 4.0
 

How long has it been since you've cleaned the throttle body? Most
don't ever do it at all. It could be a PCV valve that is damaged and
has dropped the valve portion down into the engine creating a big
vacuum leak, a really dirty throttle body or a bad spot on the TPS.
When you clean out the TB, use a very soft toothbrush and a soft cloth,
along with TB-friendly cleaner, not carb cleaner. Work with the engine
OFF, and take your time cleaning all the gunk off the sides and the
butterfly valve.

While you're in there, pull your EGR valve and give that a good
cleaning as well. Sometimes they get so gunked up that they stick
open, creating a vaccum leak.

Also, on those TPS's, aftermarket units are junk. Buy only an OEM
replacement. Same goes for the EGR valve, if you ever need to swap it
out. I found this all out the hard way.