mythreesons Posted March 28, 2011 Share Posted March 28, 2011 One of my sons mentioned this little behavior after driving one of the XJ's for a couple of days. Ever since he mentioned it, I began to notice it in other vehicles. Do they all do this or is it an indication of something else? Left over torque that "rev's" the engine once the load is gone? The behavior: Using a 4.0 w/AW-4, drive the vehicle a little and come to a stop. Change gears (ie. Drive to Reverse or the other way if your so inclined). I have noticed that when coming out of gear and going to neutral the throttle will rev up a little. Just a "blip", but it is noticeable. Tested for this behavior on all the Jeeps at the house. Here are the results: 2002 WJ (4.0/AW or NV auto tranny) - Yep, it does it. 1995 XJ (4.0/AW-4) - Yep, it does it. 1992 XJ (4.0/AW-4) - Yep it does it. 1988 MJ (4.0/AX-15) - Nope, but then it is a manual so it doesn't count. 1988 MJ (4.0/AW-4) - Ummmmmm, since it has a blown D35, it doesn't count either. 1988 XJ (4.0/AW-4) - Didn't try, it is a donor for the above MJ. I guess my data sampling is really not too good. Perhaps I should take a road trip and check other member Jeep fleets for this? (That would be kinda neat to just drive a big circle visiting as many CC members as I could for a week. Wish I could.) What do you guys think? Link to comment Share on other sites More sharing options...
JeffN Posted March 28, 2011 Share Posted March 28, 2011 It's just the air idle control circuit adjusting itself Link to comment Share on other sites More sharing options...
acfortier Posted March 28, 2011 Share Posted March 28, 2011 Most cars do it. I had a 2000 Saturn SL2 that did it, same with the 2008 KK we have and the 2005 Dodge Ram. All autos. Nothing out of the ordinary here. Link to comment Share on other sites More sharing options...
HOrnbrod Posted March 28, 2011 Share Posted March 28, 2011 When you go in gear w. the auto tranny, the hydraulic pump starts, torque converter engages, and creates a load on the engine. When you take it out of gear, the engine abruptly loses the load, and revs up a hair until the idle circuitry kicks in. Perfectly normal w. auto trannys. Link to comment Share on other sites More sharing options...
Eagle Posted March 28, 2011 Share Posted March 28, 2011 One of my sons mentioned this little behavior after driving one of the XJ's for a couple of days. Ever since he mentioned it, I began to notice it in other vehicles. Do they all do this or is it an indication of something else? Left over torque that "rev's" the engine once the load is gone? The behavior: Using a 4.0 w/AW-4, drive the vehicle a little and come to a stop. Change gears (ie. Drive to Reverse or the other way if your so inclined). I have noticed that when coming out of gear and going to neutral the throttle will rev up a little. Just a "blip", but it is noticeable. Tested for this behavior on all the Jeeps at the house. Here are the results: What else would you expect? In any gear, with an automatic the engine is pushing against the resistance of the torque converter when the vehicle is stopped. Shift into neutral and suddenly the resistance is gone. Link to comment Share on other sites More sharing options...
mythreesons Posted March 28, 2011 Author Share Posted March 28, 2011 Well it's good to know that I was headed in the right direction. After spending the day with my mother yesterday and work today, I was not real sure that my brain had any electrons left to use for thinking. Thanks guys!! Link to comment Share on other sites More sharing options...
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