Last night I notice that I had no control over where my heater and air conditioner were flowing air. After a brief search of the web I found that my heater diverter vacuum connection had become disconnected at the intake manifold like is shown here'
So I reconnected making one smal change to make the elbow fit tightly into the hose that attaches to the manifold and it works like a charm.
However on my way to work this am I notice that my idle fluctuated between about 500 and 1200 rpm making the TJ almost lurch forward. It only did it in drive after warming up and if I shifted to neutral the idle settled.
Anyone have any thoughts. I went out for some light wheelin this weekend and it was likely disconnect the entire time so I don't know if I sucked dirt into the intake through the open port. There are no other apparent vacuum leaks and other than this lurching, the jeep runs great. Thoughts???
The problem occurs when you just lightly touch the accelerator so as to inch forward and then release the accelerator (like you would do at a backed up 4 way stop sign). The idle drops just below the 1st tick mark on the speedometer (2-300 rpm) and the engine must think its dying so the throttle sensor bumps it up, which pushes the rpm to about 1200 rpm, thus the lurch forward (and you have to be quick on the brake). Its repeatable in any forward gear, but in reverse, removing your foot from the brake is enough to cause the jeep to move. In drive, you do have to press the accel to move forward.
When I disconnect the vacuum diaphragm causing a vacuum leak, the problem goes away. I guess that's why the diaphragm was in loosely when I bought the LJ. It allows the heater control to work but also allows enough leak so that the idle doesn't fluctuate.
Idle is smoother without the vacuum leak, but still smooth with it (a mild stumble). I got 16 mpg with the vacuum leak so its not exactly wrecking mileage. Also I had ok power.
Id id disconnect it a couple of weeks ago after getting a code from some E3 sparkplugs. I changed plugs to double platinum, disconnected and shorted out positive lead for 30 sec. Hooked everything back up and it ran fine...until I had this issue with the vacuum line. I've done a little more diagnosing this morning.
It only does this when the engine is warm and at a stop.
I'm going to clean the throttle body this weekend, and break out the code reader to see if it says anything but Im at a loss why the engine would operate smoother at idle with a vacuum leak than without. Are you suggesting that I do another adaptive memory clear?
Pull the positive lead off of the battery and touch it to the ground post for 30 sec. That's what I did to make the cel get reset. There's a whole procedure for resetting adaptive memory found here in post #11:
A local mechanic pluged in to my computer and it wouldnt respond at all,i took it to anothe mechanic and no responce,all fuses and such were checked up to the computer and they said were good, their saying the comp. is no good, any suggestions, im still going to reset it, might not do any good But!
Hate to bring up an old thread, but I had the exact same thing happen again. It was 99 degrees this weekend and when my wife and kid came home from driving lessons they mentioned that there was no control over which ducts the ac came out. I looked under the hood and is was at the same vacuum connection as March 2012. This time I noticed the rubber was really hot (almost felt moist). Nonetheless, I reconnected the vacuum line using some new rubber hose and that solve the ducting problem. However on my way to work today, the throttle jump was back and worse than in March 2012. When inching along in traffic there were several instances where the jeep lurched forward (rpms on deceleration went from 800 to 300 and then jumped to 1200 all in about a couple of seconds). I thought the problem was that I had a dirty TB last time but this time, I doubt that. Someone suggested that resetting the computer would solve the issue. Can anyone tell me why?
Prior to this, I've been driving the Jeep nearly daily and without event. The vacuum line was connected and performance was good. I find it hard to believe that one day of a vac line being disconnected would throw things that far out of whack. Also, with regard to the rubber vacuum line being almost moist, the engine was quite warm (just above the half way mark on the temp gage in the jeep) and the intake manifold was also very warm. Any suggestions on replacing the vacuum line with silicon lines? Right now I'm just using some old (but unused) fuel hose I had laying around the garage. I'm gonna try to look at this tonite after work although its 59 degrees today (yep 40 degrees cooler than Saturday) and raining so I'm not sure the weather is going to cooperate. Thanks
Well I reset the PCM and it worked. The fluctuation was gone this AM. I don't know why one day with the vacuum line disconnected completely disrupts more and a year of PCM operating properly, but it does...and resetting the PCM fixes all that.