robbie95 Posted August 19, 2013 Share Posted August 19, 2013 So for the past few weeks I've noticed when I rev the mj it revs fine, but then when i take my foot off the gas it feels like it wants to stall.. It has never stalled but one day it might lol. Just got it in April and haven't done much except replace the fuel filter, air filter, all the fluids etc and maybe a few other things that don't to mind. Other than that I haven't touched the thing... I've noticed when I start her up in the morning it's kind of slow to start.. so I don't know if that has anything to do with it or what. Other than that she runs like a champ... It's a 1991 mj 2.5 4 banger 186k miles on it. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 19, 2013 Share Posted August 19, 2013 Plugs, wires, cap and rotor are due to be replaced every 30,000 miles. make sure your intake manifold bolts haven't loosened up. Clean your throttle body and IAC. Courtesy of TJWalker:--------------------------------------------------------------------The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea. CLEANING THE JEEP 4.0 IDLE AIR CONTROL Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to) “Gently” wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it. Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 19, 2013 Share Posted August 19, 2013 Did you disconnect your battery lately? You have a 91, first year of the OBD1 ignition system. Whenever you disconnect the battery to work on it, the ECU (computer) defaults to it's stored settings. It'll take 100-150 miles of driving for the ECU to relearn the new sensor inputs again. During this time it will want to stall, but the more you drive it gradually gets better and soon you will be golden again. In order to prevent the ECU "relearning" process, don't disconnect the the battery unless absolutely necessary. If it is necessary and your repair won't take too long, place a standard 9 VDC battery modified with leads and alligator clips in parallel with your battery before disconnecting so the ECU will retain power and keep it's memory. Link to comment Share on other sites More sharing options...
robbie95 Posted August 19, 2013 Author Share Posted August 19, 2013 Plugs, wires, cap and rotor are due to be replaced every 30,000 miles. make sure your intake manifold bolts haven't loosened up. Clean your throttle body and IAC. Courtesy of TJWalker: -------------------------------------------------------------------- The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea. CLEANING THE JEEP 4.0 IDLE AIR CONTROL Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to) “Gently” wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it. Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled I'm gonna try cleaning the IAC, because when I cleaned the throttle body.. it was disgusting, so maybe the IAC is nasty also. Link to comment Share on other sites More sharing options...
robbie95 Posted August 19, 2013 Author Share Posted August 19, 2013 Did you disconnect your battery lately? You have a 91, first year of the OBD1 ignition system. Whenever you disconnect the battery to work on it, the ECU (computer) defaults to it's stored settings. It'll take 100-150 miles of driving for the ECU to relearn the new sensor inputs again. During this time it will want to stall, but the more you drive it gradually gets better and soon you will be golden again. In order to prevent the ECU "relearning" process, don't disconnect the the battery unless absolutely necessary. If it is necessary and your repair won't take too long, place a standard 9 VDC battery with leads and alligator clips in parallel with your battery before disconnecting so the ECU will retain power and keep it's memory. battery died a few days ago because I was running the radio without starting it.. could that do it too? Link to comment Share on other sites More sharing options...
cruiser54 Posted August 19, 2013 Share Posted August 19, 2013 Did you disconnect your battery lately? You have a 91, first year of the OBD1 ignition system. Whenever you disconnect the battery to work on it, the ECU (computer) defaults to it's stored settings. It'll take 100-150 miles of driving for the ECU to relearn the new sensor inputs again. During this time it will want to stall, but the more you drive it gradually gets better and soon you will be golden again. In order to prevent the ECU "relearning" process, don't disconnect the the battery unless absolutely necessary. If it is necessary and your repair won't take too long, place a standard 9 VDC battery with leads and alligator clips in parallel with your battery before disconnecting so the ECU will retain power and keep it's memory. battery died a few days ago because I was running the radio without starting it.. could that do it too? Yep. But since this is new to you, do yourself a favor and get new tuneup parts on it, check every gearbox level and grease the chassis and drivetrain. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 19, 2013 Share Posted August 19, 2013 :agree: Plus change all the fluids, as you already have started on. Link to comment Share on other sites More sharing options...
robbie95 Posted August 19, 2013 Author Share Posted August 19, 2013 Did you disconnect your battery lately? You have a 91, first year of the OBD1 ignition system. Whenever you disconnect the battery to work on it, the ECU (computer) defaults to it's stored settings. It'll take 100-150 miles of driving for the ECU to relearn the new sensor inputs again. During this time it will want to stall, but the more you drive it gradually gets better and soon you will be golden again. In order to prevent the ECU "relearning" process, don't disconnect the the battery unless absolutely necessary. If it is necessary and your repair won't take too long, place a standard 9 VDC battery with leads and alligator clips in parallel with your battery before disconnecting so the ECU will retain power and keep it's memory. battery died a few days ago because I was running the radio without starting it.. could that do it too? Yep. But since this is new to you, do yourself a favor and get new tuneup parts on it, check every gearbox level and grease the chassis and drivetrain. Will do, I wouldn't know where to start with the distributor cap though.. Is there a manual that I can get somewhere to help me do all this stuff that gets a little complicated? Link to comment Share on other sites More sharing options...
robbie95 Posted August 19, 2013 Author Share Posted August 19, 2013 :agree: Plus change all the fluids, as you already have started on. got everything changed except rear diff fluid... gonna change that when it stops raining... if it ever does lol Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 19, 2013 Share Posted August 19, 2013 Invest in a 1991 factory service manual (FSM) set; best tool you ever can purchase. It will pay for itself many times over if you plan on doing your own maintenance and repairs. Ebay or elsewhere. Link to comment Share on other sites More sharing options...
robbie95 Posted August 19, 2013 Author Share Posted August 19, 2013 Invest in a 1991 factory service manual (FSM) set; best tool you ever can purchase. It will pay for itself many times over if you plan on doing your own maintenance and repairs. Ebay or elsewhere. Well, I would like to do my own repairs but if it gets too complicated and needs specialty tools to do then that's is the only time I probably won't try to fix it myself. Yea, I'll have to invest in one of those.. probably order one tomorrow lol.. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 19, 2013 Share Posted August 19, 2013 Invest in a 1991 factory service manual (FSM) set; best tool you ever can purchase. It will pay for itself many times over if you plan on doing your own maintenance and repairs. Ebay or elsewhere. Well, I would like to do my own repairs but if it gets too complicated and needs specialty tools to do then that's is the only time I probably won't try to fix it myself. Yea, I'll have to invest in one of those.. probably order one tomorrow lol.. The things mentioned are easy and rquire basic tools. Link to comment Share on other sites More sharing options...
87MJTIM Posted August 19, 2013 Share Posted August 19, 2013 I found this site for FSM. Complete set and reasonable prices. www.faxonautoliterature.com Link to comment Share on other sites More sharing options...
robbie95 Posted August 19, 2013 Author Share Posted August 19, 2013 Went outside today and did a few things to the comanche, including cleaning the IAC valve.. Was really dirty.. I cleaned it.. reinstalled it.. started her up.. and I could notice a difference in the idle but the revving problem is still there. Guess I'm gonna have to do the other stuff y'all mentioned.. and hope it works! Thanks for the help btw and for the link. Link to comment Share on other sites More sharing options...
robbie95 Posted August 19, 2013 Author Share Posted August 19, 2013 Alright, so I was fiddling through some wires and I found this wire (pic will be down below hopefully..) I followed it down and it goes near the o2 sensor.. why is this not plugged up and if it should be what should it be plugged into? Link to comment Share on other sites More sharing options...
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