XEON
04-03-2005, 08:50 PM
Here is a post from Jeepforums about my Idle issues. I figured I would post this for anyone else with the same issues. Start a small trouble shooting database :D Hope this helps out!
xeon 03-26-2005 12:36 PM
YJ 2.5L 4cyl idle problems
I have a 88 YJ with a 2.5L 4 banger.
The idle is perfect after starting and running for a few miles. But after some highway driving and a stop light. I noticed the egine idles at about 1500 RPM. Now if I turn the engine off and let it sit for a few minutes then start it, it idles fine again just at 1000 rpm.
I would like to know whats going on? And how I can fix this problem. I mean I dont mind that much but it gets annoying at stop lights when it s idleing that fast.
Thanks and any help is apreciated! :wave:
boomhower 03-26-2005 12:48 PM
Wish I had a definate answer for you. I've got a 91 4 cyl, but that was the first year of Multi-Port Injection. I believe earlier 4cyl YJ's had the standard Throttle Body Injection, which is a bit different. My RPM's drop way too low after revving the engine past 3000 RPM's (I mean like it almost stalls), and I thought about replacing the TPS (throttle positioning sensor).
It definetly sounds like it has to be a sensor or something electrical, if it runs fine in different scenarios. Otherwise I would say clean out your throttle body. If I get a chance I'll look for my Haynes manual and should be able to find you a better answer.
xeon 03-31-2005 05:53 PM
Does anyone have any other clues? I am just thinking of pulling apart my intake and cleaning sensors and stuff. Let me know thanks! :cool:
sentinal02 03-31-2005 06:53 PM
Quote:
Originally Posted by xeon
Does anyone have any other clues? I am just thinking of pulling apart my intake and cleaning sensors and stuff. Let me know thanks! :cool:
sounds like one of the temp sensors is off. either the CTS or the MAT. you can check both with an ohm meter. chilton's has a table of what the values should be at a given temp. the resistance is designed to drop as the temp goes up, so if your sensor is going bad, or has a bad connection, the computer sees a low temp resistance and compensates for what it thinks is a cold engine/cold start with a faster idle/more gas. normally electrical resistance increases as temperature goes up (ie hot wires have a higher resistance than cold ones), so a hot sensor that is going bad will increase resistance until it looks like an open circuit. mine used to idle at 1K at operating temp until i found the CTS wasn't hooked up right. i'd start there. shouldn't be hard to test with a multimeter. HTH
xeon 03-31-2005 06:59 PM
Quote:
Originally Posted by sentinal02
sounds like one of the temp sensors is off. either the CTS or the MAT. you can check both with an ohm meter. chilton's has a table of what the values should be at a given temp. the resistance is designed to drop as the temp goes up, so if your sensor is going bad, or has a bad connection, the computer sees a low temp resistance and compensates for what it thinks is a cold engine/cold start with a faster idle/more gas. normally electrical resistance increases as temperature goes up (ie hot wires have a higher resistance than cold ones), so a hot sensor that is going bad will increase resistance until it looks like an open circuit. mine used to idle at 1K at operating temp until i found the CTS wasn't hooked up right. i'd start there. shouldn't be hard to test with a multimeter. HTH
Thanks sen for the info. I hope the Hayes has that info... the book cost $20 and it really only helped me with torqu specs... :D. I might haev to buy Chiltons to get all info I need. Thanks a bunch. Maybe if you get a chance scan that page and post it. Thanks!
drew2000 03-31-2005 07:21 PM
IIRC RPM @ idle should be ~750 RPM.
Drew
sentinal02 03-31-2005 07:30 PM
Quote:
Originally Posted by drew2000
IIRC RPM @ idle should be ~750 RPM.
Drew
yes and he already knows that his is off at 1500 :thumbsup: mine idled at 1K before fixing the sensor and now sits at about 800 at op temp.
sentinal02 03-31-2005 07:43 PM
lol, was just looking through my haynes and found this under the MAT sensor
"checking the MAT sensor is beyond the scope of the home mechanic. take the vehicle to a dealer service department or other qualified shop for diagnosis"
apparently the home mechanic can't read, and thus doesn't own, an ohm meter. that must be why haynes' wiring diagrams are so hard to read. they can't do electrical work anyway so why bother. definitely get a chilton's X, haynes does ok for the later model engines, but the 4.2 and the TBI 2.5 are covered much better in the chilton's. chilton's also gives a lot more diagnosing info as opposed to the above statement. anyway, here's the table i mentioned earlier. HTH
temp °F.............Ohms
212...................185
160...................450
100...................1600
70.....................3400
40.....................7500
20.....................13500
0.......................25000
-40....................100700
and just as a side note to anyone else reading this, these values are only good for the TBI 2.5 sensors. the later model sensors use totally different values.
xeon 03-26-2005 12:36 PM
YJ 2.5L 4cyl idle problems
I have a 88 YJ with a 2.5L 4 banger.
The idle is perfect after starting and running for a few miles. But after some highway driving and a stop light. I noticed the egine idles at about 1500 RPM. Now if I turn the engine off and let it sit for a few minutes then start it, it idles fine again just at 1000 rpm.
I would like to know whats going on? And how I can fix this problem. I mean I dont mind that much but it gets annoying at stop lights when it s idleing that fast.
Thanks and any help is apreciated! :wave:
boomhower 03-26-2005 12:48 PM
Wish I had a definate answer for you. I've got a 91 4 cyl, but that was the first year of Multi-Port Injection. I believe earlier 4cyl YJ's had the standard Throttle Body Injection, which is a bit different. My RPM's drop way too low after revving the engine past 3000 RPM's (I mean like it almost stalls), and I thought about replacing the TPS (throttle positioning sensor).
It definetly sounds like it has to be a sensor or something electrical, if it runs fine in different scenarios. Otherwise I would say clean out your throttle body. If I get a chance I'll look for my Haynes manual and should be able to find you a better answer.
xeon 03-31-2005 05:53 PM
Does anyone have any other clues? I am just thinking of pulling apart my intake and cleaning sensors and stuff. Let me know thanks! :cool:
sentinal02 03-31-2005 06:53 PM
Quote:
Originally Posted by xeon
Does anyone have any other clues? I am just thinking of pulling apart my intake and cleaning sensors and stuff. Let me know thanks! :cool:
sounds like one of the temp sensors is off. either the CTS or the MAT. you can check both with an ohm meter. chilton's has a table of what the values should be at a given temp. the resistance is designed to drop as the temp goes up, so if your sensor is going bad, or has a bad connection, the computer sees a low temp resistance and compensates for what it thinks is a cold engine/cold start with a faster idle/more gas. normally electrical resistance increases as temperature goes up (ie hot wires have a higher resistance than cold ones), so a hot sensor that is going bad will increase resistance until it looks like an open circuit. mine used to idle at 1K at operating temp until i found the CTS wasn't hooked up right. i'd start there. shouldn't be hard to test with a multimeter. HTH
xeon 03-31-2005 06:59 PM
Quote:
Originally Posted by sentinal02
sounds like one of the temp sensors is off. either the CTS or the MAT. you can check both with an ohm meter. chilton's has a table of what the values should be at a given temp. the resistance is designed to drop as the temp goes up, so if your sensor is going bad, or has a bad connection, the computer sees a low temp resistance and compensates for what it thinks is a cold engine/cold start with a faster idle/more gas. normally electrical resistance increases as temperature goes up (ie hot wires have a higher resistance than cold ones), so a hot sensor that is going bad will increase resistance until it looks like an open circuit. mine used to idle at 1K at operating temp until i found the CTS wasn't hooked up right. i'd start there. shouldn't be hard to test with a multimeter. HTH
Thanks sen for the info. I hope the Hayes has that info... the book cost $20 and it really only helped me with torqu specs... :D. I might haev to buy Chiltons to get all info I need. Thanks a bunch. Maybe if you get a chance scan that page and post it. Thanks!
drew2000 03-31-2005 07:21 PM
IIRC RPM @ idle should be ~750 RPM.
Drew
sentinal02 03-31-2005 07:30 PM
Quote:
Originally Posted by drew2000
IIRC RPM @ idle should be ~750 RPM.
Drew
yes and he already knows that his is off at 1500 :thumbsup: mine idled at 1K before fixing the sensor and now sits at about 800 at op temp.
sentinal02 03-31-2005 07:43 PM
lol, was just looking through my haynes and found this under the MAT sensor
"checking the MAT sensor is beyond the scope of the home mechanic. take the vehicle to a dealer service department or other qualified shop for diagnosis"
apparently the home mechanic can't read, and thus doesn't own, an ohm meter. that must be why haynes' wiring diagrams are so hard to read. they can't do electrical work anyway so why bother. definitely get a chilton's X, haynes does ok for the later model engines, but the 4.2 and the TBI 2.5 are covered much better in the chilton's. chilton's also gives a lot more diagnosing info as opposed to the above statement. anyway, here's the table i mentioned earlier. HTH
temp °F.............Ohms
212...................185
160...................450
100...................1600
70.....................3400
40.....................7500
20.....................13500
0.......................25000
-40....................100700
and just as a side note to anyone else reading this, these values are only good for the TBI 2.5 sensors. the later model sensors use totally different values.