rustybottoms88 Posted February 26, 2015 Share Posted February 26, 2015 I have changed fuel filter, injectors, cap and rotor, spark plugs, ECM, and CPS, check out my thread "Em's MJ" but long story short the truck won't idle. I had a brick on the gas pedal to keep the truck running so I could check vac pressure and when i pulled the vac line on the intake the truck surged. I took the brick off the gas pedal and it idles. I traced the vac line to the front of the engine to a round plastic ball just behind the front bumper. Another small plastic line attached to it as well. I took the ball off and it has water in it, I can here it slosh around in it. I blew air through the vac hose and its clear. Any idea what is going on here? Generally when you unplug a vac line an engine will run rough and shake quite, the opposite here. BTW Vacuum was rock solid at 25# with throttle slightly open. Fuel pressure is with in spec. I would post pics but for some reason when i right click the paste option is not working...... Link to comment Share on other sites More sharing options...
Jeep Driver Posted February 26, 2015 Share Posted February 26, 2015 Have you cleaned the TB? Link to comment Share on other sites More sharing options...
rustybottoms88 Posted February 26, 2015 Author Share Posted February 26, 2015 Have you cleaned the TB? Nope, I did unplug the TPS tho while i was cleaning plugins. Are u suppose to recalibrate it if you unplug,even it with the engine off? Link to comment Share on other sites More sharing options...
MJCARENA Posted February 26, 2015 Share Posted February 26, 2015 Maybe your idle speed control valve is stuck shut or plugged up with carbon, and when you pulled the line off it got enough air for it to idle again. Like Jeep Driver asked, did you clean your TB? Link to comment Share on other sites More sharing options...
rustybottoms88 Posted February 26, 2015 Author Share Posted February 26, 2015 Maybe your idle speed control valve is stuck shut or plugged up with carbon, and when you pulled the line off it got enough air for it to idle again. Like Jeep Driver asked, did you clean your TB? I thought the same thing. I have had the IAC out and cleaned it tho (it looked brand new) but it could be stuck shut or malfunctioning somehow. I mentioned above that I have not cleaned the TB. Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted February 27, 2015 Share Posted February 27, 2015 Under normal operation there are only two ways air can enter the motor, either the throttle body butterfly valve opening or the IAC valve opening. If you are not pressing the gas pedal and the IAC valve is stuck closed there is no airflow and the engine cannot run. Thus the reason why the engine idled when you pulled a vac line. I have changed fuel filter, injectors, cap and rotor, spark plugs, ECM, and CPS, check out my thread "Em's MJ" but long story short the truck won't idle. I had a brick on the gas pedal to keep the truck running so I could check vac pressure and when i pulled the vac line on the intake the truck surged. I took the brick off the gas pedal and it idles. I traced the vac line to the front of the engine to a round plastic ball just behind the front bumper. Another small plastic line attached to it as well. I took the ball off and it has water in it, I can here it slosh around in it. I blew air through the vac hose and its clear. Any idea what is going on here? Generally when you unplug a vac line an engine will run rough and shake quite, the opposite here. BTW Vacuum was rock solid at 25# with throttle slightly open. Fuel pressure is with in spec. I would post pics but for some reason when i right click the paste option is not working...... The round plastic ball you mentioned is for the climate control system and is more or less irrelevant to your problem. Replace the IAC and your problem will be solved. Link to comment Share on other sites More sharing options...
rustybottoms88 Posted March 1, 2015 Author Share Posted March 1, 2015 Under normal operation there are only two ways air can enter the motor, either the throttle body butterfly valve opening or the IAC valve opening. If you are not pressing the gas pedal and the IAC valve is stuck closed there is no airflow and the engine cannot run. Thus the reason why the engine idled when you pulled a vac line. I have changed fuel filter, injectors, cap and rotor, spark plugs, ECM, and CPS, check out my thread "Em's MJ" but long story short the truck won't idle. I had a brick on the gas pedal to keep the truck running so I could check vac pressure and when i pulled the vac line on the intake the truck surged. I took the brick off the gas pedal and it idles. I traced the vac line to the front of the engine to a round plastic ball just behind the front bumper. Another small plastic line attached to it as well. I took the ball off and it has water in it, I can here it slosh around in it. I blew air through the vac hose and its clear. Any idea what is going on here? Generally when you unplug a vac line an engine will run rough and shake quite, the opposite here. BTW Vacuum was rock solid at 25# with throttle slightly open. Fuel pressure is with in spec. I would post pics but for some reason when i right click the paste option is not working...... The round plastic ball you mentioned is for the climate control system and is more or less irrelevant to your problem. Replace the IAC and your problem will be solved. Thanks. I did some more work on it yesterday morning and unplugged the IAC. It would idle barley for a few seconds then peter out. I had a IAC i had gutted awhile bac for diagnostic purposes so I installed that and it idled but was high, as expected, but it was smooth and consistent so I have a new IAC on the way. Thank for the help Link to comment Share on other sites More sharing options...
rustybottoms88 Posted March 6, 2015 Author Share Posted March 6, 2015 Installed the new IACV today. Idles like a dream! No more feathering the throttle when stopped. Thanks for the help. Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted March 6, 2015 Share Posted March 6, 2015 Sweet deal, thanks for following up with us. :thumbsup: Link to comment Share on other sites More sharing options...
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