Part Throttle Hesitation
04-28-2009, 01:12 PM
#1
Junior Member
Thread Starter
Part Throttle Hesitation
I have a 98 Cherokee with a 4.0 that is completely stock. The problem that I'm having is that sometimes at part throttle (only when starting from a dead stop) it hesitates/looses power till I let off the throttle and get back on it. Then everything is fine. The other day when it happened, I went into the throttle a little more and it seemed to backfire in the throttle body. I have already replaced my TPS and it seemed to go away for a week or so. Front O2 is less that a year old too. Any ideas?
04-29-2009, 02:51 PM
#3
Newbie
Join Date: Apr 2009
Posts: 9
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee
Same issue!
Hope I'm not threadjacking here, but I'm looking at the same problem on my cousins 98 Cherokee Sport, 4.0L. Random/intermittent stumble/hesitation at idle and part throttle operation. Blipping the throttle a few times seems to make it all even out. Appears to only occur during closed loop operation. Spark plugs/rotor/cap/wires replaced, new intake manifold gasket, not hearing any vacuum leaks with stethoscope. The computer is throwing a code for the O2 sensor, but the sensor looks brand new and the cable to it is dangling suggesting someone replaced it not all that long ago, perhaps due to the stumbling. Jiggling the wire harness does not reproduce results.
I've heard of people having this issue and replacing their IAC motor. The only thing I can think of with the IAC causing problems would be letting unmetered air past the throttle plate, so the reading from the MAP and TPS conflict with each other, or something like that?
Ehhhh!!!
Thanks!
I've heard of people having this issue and replacing their IAC motor. The only thing I can think of with the IAC causing problems would be letting unmetered air past the throttle plate, so the reading from the MAP and TPS conflict with each other, or something like that?
Ehhhh!!!
Thanks!
04-29-2009, 02:57 PM
#4
CF Veteran
Join Date: Nov 2008
Location: Paso Robles Ca
Posts: 2,473
Likes: 0
Received 9 Likes
on
9 Posts
Year: 1991
Model: Cherokee
Engine: 4.0
several thing that can cause you problem
got to auto part house and have them check for codes
check for vacuum leeks
check or replace TPS
check or replace MAP sensor
check or replace CPS
check or replace IAC
got to auto part house and have them check for codes
check for vacuum leeks
check or replace TPS
check or replace MAP sensor
check or replace CPS
check or replace IAC
04-29-2009, 03:10 PM
#5
Newbie
Join Date: Apr 2009
Posts: 9
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee
several thing that can cause you problem
got to auto part house and have them check for codes
check for vacuum leeks ->in my case, no vacuum leaks found.
check or replace TPS ->I disconnected the connector and ran the sensor through its full range with an ohm-meter attached. Smooth numbers through the scale.
check or replace MAP sensor ->can you, or anyone, give us a heads up on the wiring diagram to the MAP? What readings to look for
check or replace CPS ->by what I've been reading about the CPS, it seems to me that the symptom is slightly different than what I'm noticing. With a CPS, correct me if I'm wrong, the engine noticeably *dies* and then catches back up, just like someone pulled the power to it (which, in a way, is kinda true).
check or replace IAC ->in my case, i pulled the IAC to look at it, and it seems like the plunger doesn't actuate the way it should. It's a stepper motor(EDIT FOR FUTURE READERS: apparently, it ISN'T a stepper motor, my bad!) so does the plunger rotate to extend and retract? And again, would the IAC actually be a culprit to a part throttle hesitation?
got to auto part house and have them check for codes
check for vacuum leeks ->in my case, no vacuum leaks found.
check or replace TPS ->I disconnected the connector and ran the sensor through its full range with an ohm-meter attached. Smooth numbers through the scale.
check or replace MAP sensor ->can you, or anyone, give us a heads up on the wiring diagram to the MAP? What readings to look for
check or replace CPS ->by what I've been reading about the CPS, it seems to me that the symptom is slightly different than what I'm noticing. With a CPS, correct me if I'm wrong, the engine noticeably *dies* and then catches back up, just like someone pulled the power to it (which, in a way, is kinda true).
check or replace IAC ->in my case, i pulled the IAC to look at it, and it seems like the plunger doesn't actuate the way it should. It's a stepper motor(EDIT FOR FUTURE READERS: apparently, it ISN'T a stepper motor, my bad!) so does the plunger rotate to extend and retract? And again, would the IAC actually be a culprit to a part throttle hesitation?
Last edited by genericflounder; 04-29-2009 at 03:33 PM. Reason: Just a quick notation on incorrect information.
04-29-2009, 03:22 PM
#7
CF Veteran
Join Date: Nov 2008
Location: Paso Robles Ca
Posts: 2,473
Likes: 0
Received 9 Likes
on
9 Posts
Year: 1991
Model: Cherokee
Engine: 4.0
with a 98 you have the newer map sensor i think
on my 91 it have three wires
ground
power should have 5 volt
power to the ecm should be 5 volt engine of and 2to3 volts ruining
on my 91 it have three wires
ground
power should have 5 volt
power to the ecm should be 5 volt engine of and 2to3 volts ruining
Last edited by mike37; 04-29-2009 at 03:49 PM.
Trending Topics
04-29-2009, 03:37 PM
#8
Newbie
Join Date: Apr 2009
Posts: 9
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee
Nice to know about the IAC - I could have sworn I read about it being a stepper motor. This one is stuck, I have to realllllly push on the bugger to get it to budge. If anything, at least we know it's bad and I won't feel bad about replacing it even if it doesn't fix the problem :P
Last edited by genericflounder; 04-29-2009 at 03:38 PM. Reason: Added link to sticky.
04-29-2009, 03:48 PM
#9
CF Veteran
Join Date: Nov 2008
Location: Paso Robles Ca
Posts: 2,473
Likes: 0
Received 9 Likes
on
9 Posts
Year: 1991
Model: Cherokee
Engine: 4.0
I saw there was a nice write-up for the CPS checking in a sticky (LINK!: https://www.cherokeeforum.com/showthread.php?t=5563 ), I'll do it for kicks and grins.
Nice to know about the IAC - I could have sworn I read about it being a stepper motor. This one is stuck, I have to realllllly push on the bugger to get it to budge. If anything, at least we know it's bad and I won't feel bad about replacing it even if it doesn't fix the problem :P
Nice to know about the IAC - I could have sworn I read about it being a stepper motor. This one is stuck, I have to realllllly push on the bugger to get it to budge. If anything, at least we know it's bad and I won't feel bad about replacing it even if it doesn't fix the problem :P
but they are just a little spring loaded magnetic valve
that controls the idle air mixture
04-29-2009, 04:05 PM
#11
Newbie
Join Date: Apr 2009
Posts: 9
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee
I did witness it once where it was sitting at idle, and the stumble came in. You can hear it run rough and see it shake, and also the RPM's at one point revved up a bit (by itself) and came back down and kept stumbling. Apparently it has done this other times as well.
04-29-2009, 05:32 PM
#12
Seasoned Member
Join Date: Apr 2009
Location: Northeast PA
Posts: 288
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1997
Model: Cherokee
Engine: 4.0, k&n intake Flomaster cat back
I have a 98 Cherokee with a 4.0 that is completely stock. The problem that I'm having is that sometimes at part throttle (only when starting from a dead stop) it hesitates/looses power till I let off the throttle and get back on it. Then everything is fine. The other day when it happened, I went into the throttle a little more and it seemed to backfire in the throttle body. I have already replaced my TPS and it seemed to go away for a week or so. Front O2 is less that a year old too. Any ideas?
04-30-2009, 08:34 AM
#13
Newbie
Join Date: Apr 2009
Posts: 9
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee
I have a 98 Cherokee with a 4.0 that is completely stock. The problem that I'm having is that sometimes at part throttle (only when starting from a dead stop) it hesitates/looses power till I let off the throttle and get back on it. Then everything is fine. The other day when it happened, I went into the throttle a little more and it seemed to backfire in the throttle body. I have already replaced my TPS and it seemed to go away for a week or so. Front O2 is less that a year old too. Any ideas?
EloXJ,
I'm curious as to whether or not you've dug up more information?
Also, has my description coincided with your issue as well? Just wondering if we're looking at the same problem here.
Thanks!
04-30-2009, 12:10 PM
#14
Junior Member
Thread Starter
Seems like we do have the same problem though except I'm not throwing any codes. Just added some Seafoam to the tank last night for kicks.