rough idle, code 15, speedometer works - JeepForum.com

 
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post #1 of 9 Old 10-18-2009, 03:43 PM Thread Starter
kornonthekob99
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rough idle, code 15, speedometer works

ive searched the answer all over this forum but cant seem to figure out exactly what im looking for... someone else had a similar problem but no one ever responded...

i was driving home the other day and as i was cruising in 4th it felt as if i was getting some resistance.. then it would drive normal, and then resist again... on and off... at a red light a realized my idle was very jumpy, going from 1100 to 700 every few seconds or so... i rode my gears up high in order to prevent from stalling out so i could get home... half way home, the misfiring stopped and it drove fine till i got home....

i ran codes, got a 15, distance sensor or circuit...i read that there is the Vehicle Speed Sensor on the back of the transfer case, and the speedometer itself... my speedo works, i CAN see how fast i am going, so thats not the problem... i heard that the air/fuel ratio is also controlled by the VSS so if that part is off, then the jeep will misfire...

my problem now is that i dont know if i have a faulty VSS, and i dont know exactly which part that refers to, there is a sensor and a cable attached to it.. also i read that there is a gear in there... i dont want to throw down 100 dollars and be wrong, what should i check first? any good diagrams for whats going on down there?

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post #2 of 9 Old 10-18-2009, 05:02 PM
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Quote:
Originally Posted by kornonthekob99 View Post
ive searched the answer all over this forum but cant seem to figure out exactly what im looking for... someone else had a similar problem but no one ever responded...

i was driving home the other day and as i was cruising in 4th it felt as if i was getting some resistance.. then it would drive normal, and then resist again... on and off... at a red light a realized my idle was very jumpy, going from 1100 to 700 every few seconds or so... i rode my gears up high in order to prevent from stalling out so i could get home... half way home, the misfiring stopped and it drove fine till i got home....

i ran codes, got a 15, distance sensor or circuit...i read that there is the Vehicle Speed Sensor on the back of the transfer case, and the speedometer itself... my speedo works, i CAN see how fast i am going, so thats not the problem... i heard that the air/fuel ratio is also controlled by the VSS so if that part is off, then the jeep will misfire...

my problem now is that i dont know if i have a faulty VSS, and i dont know exactly which part that refers to, there is a sensor and a cable attached to it.. also i read that there is a gear in there... i dont want to throw down 100 dollars and be wrong, what should i check first? any good diagrams for whats going on down there?
Your '91 (like my '91) is a bastard child.

It DOES have a VSS signal generator mounted in the T-case that feeds a VSS signal (8 pulses per revolution) to the ECM for engine management purposes.

It ALSO has a speedo cable that mechanically operates the speedometer. This is why you can get a fault code for the VSS signal & still have a working speedometer.

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post #3 of 9 Old 10-18-2009, 05:28 PM
idaholtby
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Check the electrical connection for the VSS output to the ecm. If good, you lilely need a new sender. Like MeanMax said, the '91 is an odd duck. Here is a picture if you are unsure...
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post #4 of 9 Old 10-18-2009, 09:41 PM Thread Starter
kornonthekob99
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o well thats good that my speedo sstill works i guess haha...

yea thats the part i was looking at, i disconnected the sensor connection and replugged it in... am i testing its ohm reading? not sure what i am looking for.. i am just using my pop's car for the time being to avoid getting stuck till i have a moment to look into it further
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post #5 of 9 Old 11-10-2009, 12:59 PM Thread Starter
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so i replaced the part... and added an o2 sensor, which was not on the car when i bought it.. it drives better and a lt smoother for the most part, but there are still moments where the car will run rough, and chug chug on me, like its misfiring... not sure if it could still be the parts the just replaced... it wouldnt make sense... i am guesing maybe its al the deposits left in there that just need cleaning out from all the years it probably ran rich from no o2 sensor... any thoughts? ill run codes later again
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post #6 of 9 Old 11-10-2009, 01:01 PM
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Time for a tuneup probably if you were not running an o2. At least plugs and oil change.


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post #7 of 9 Old 11-10-2009, 03:30 PM
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Did you clear the codes ?

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post #8 of 9 Old 11-11-2009, 05:23 PM Thread Starter
kornonthekob99
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i gave the car a tuneup when i bought it about 4 months ago, it def needs an oil change now... an i did leave the battery unhooked for a while and then i installed those parts but i havent had a chance to actually see if they cleared, im gonna have to check later
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post #9 of 9 Old 11-22-2009, 05:01 PM Thread Starter
kornonthekob99
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finally got a chance to change rotrs nd pads, and while i was at it, i checked codes again... i am getting a 21.. i had cleared the codes for sure because i was getting codes for the intake sensor and for it running rich and for the speed sensor before but now its only the 21... still confused as to why... i just installed an o2 sensor.. what shoul i check?
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