88 cherokee high idle,vacuum leaks,runnning rich
09-23-2014, 03:28 PM
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88 cherokee high idle,vacuum leaks,runnning rich
ive got an 88 Cherokee 4.0 and it idles very weird. starts at 850 and bounces from there to 1k. I know there are vacuum leaks. the po capped almost every single vacuum line in the engine bay. it runs fine besides the high idle and no use of hvac or cruise or 4x4 dash lights. but I want these to work for this winter. it also backfires through the exhaust when revved up. ive cleaned every connection I can get my hands on and done all of cruisers tips but im at a loss and hoping you guys can help me figure this out. vacuum leaks causing the idle.. but would it cause it to run rich? o2 sensor?
Last edited by 88jeepcherokeexj; 09-23-2014 at 04:09 PM.
09-23-2014, 10:19 PM
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Yep. Me.
Make sure your intake manifold bolts aren't loose. Get the vacuum harnesses replaced. Post 22 in my tips. Use this diagram to orient you. Go from there.
Make sure your intake manifold bolts aren't loose. Get the vacuum harnesses replaced. Post 22 in my tips. Use this diagram to orient you. Go from there.
09-23-2014, 11:02 PM
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Yes, Him^. (the grumpy one)(Kidding!). As you go through getting if back, do note;
There is a brittle little tube. It comes out of a rubber plug, low on the engine side of the throttle body. It runs back to the firewall, then up to your MAP sensor sort of high up there near center on the firewall. CRUCIAL!! The MAP will tell the ECU to dump fuel with less/no vacuum. Any crack or blockage will cause problems.
Besides that, it's also important that the large front tube on the Valve Cover is free to vent....to the air cleaner.
There is a brittle little tube. It comes out of a rubber plug, low on the engine side of the throttle body. It runs back to the firewall, then up to your MAP sensor sort of high up there near center on the firewall. CRUCIAL!! The MAP will tell the ECU to dump fuel with less/no vacuum. Any crack or blockage will cause problems.
Besides that, it's also important that the large front tube on the Valve Cover is free to vent....to the air cleaner.
09-23-2014, 11:05 PM
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Yes, Him^. (the grumpy one)(Kidding!). As you go through getting if back, do note;
There is a brittle little tube. It comes out of a rubber plug, low on the engine side of the throttle body. It runs back to the firewall, then up to your MAP sensor sort of high up there near center on the firewall. CRUCIAL!! The MAP will tell the ECU to dump fuel with less/no vacuum. Any crack or blockage will cause problems.
Besides that, it's also important that the large front tube on the Valve Cover is free to vent....to the air cleaner.
There is a brittle little tube. It comes out of a rubber plug, low on the engine side of the throttle body. It runs back to the firewall, then up to your MAP sensor sort of high up there near center on the firewall. CRUCIAL!! The MAP will tell the ECU to dump fuel with less/no vacuum. Any crack or blockage will cause problems.
Besides that, it's also important that the large front tube on the Valve Cover is free to vent....to the air cleaner.
09-23-2014, 11:54 PM
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See? I told you he gets grumpy. Truthfully though Pete, I thought the verbal description was adequate, and saves a little bandwidth on the server, (or something like that). And my thanks for telling me about it back in 2011!
09-23-2014, 11:57 PM
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Hey, maybe I could add your description to the photo!!!
Last edited by cruiser54; 09-24-2014 at 12:14 AM.
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09-24-2014, 12:24 AM
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Sure! Do you remember when a poster nearly ignored yours, and went on to thank me for mine? (my one and only, brief moment in the sun).
09-24-2014, 08:04 AM
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09-24-2014, 10:54 AM
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Map sensor was the first thing I checked.. I might be trading it today for a 79 wagoneer, if that falls through ill get to work replacing the vacuum harness
09-24-2014, 03:11 PM
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ill probably keep my jeep. makes more scence.. ive replaced almost everything and all is good on it besides these issues. and a fullsize wont fit down trails here... ill start replacing all the vacuum hoses and such. I also don't have the vacuum ball thingy, that of any importance? also found out my iac is dead I believe. if I unplug it while running nothing changes
Last edited by 88jeepcherokeexj; 09-24-2014 at 03:41 PM.
09-25-2014, 05:42 PM
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ElMartillo (11-16-2019)
09-25-2014, 07:53 PM
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Does the Job OK! I little writeup on dealing with the broken stub in the rubber might be in order.
I was actually talking about the tube to it...sounds like you checked that as well...Just...it doesn't really look as importand as it is.
I wonder if a guy could (carefully), use a hose on low to check for manifold vacuum leaks on a cold engine. I just use starting fluid, but nobody likes posting that because that can go so wrong. On a warm engine short shots will evaporate right away and not accumulate. IN any case you might see if any easy to reach bolts seem loose. If so you ramove the air cleaner and tighten them all, starting in the center and working out.
Also don't forget the power steering....And the EGR valve.
The IAC has a motor that is controlled by the ECU which sets the airflow through it, around the throttle plate. Unplugging it just leaves it set where it was.
The Vacuum ball, (and a check valve), holds vacuum for controls while the intake manifold vacuum crashes when you have your foot in it. A completely harmless cridder, that keeps your vents blowing right, your disco & light, and your cruse working.
I was actually talking about the tube to it...sounds like you checked that as well...Just...it doesn't really look as importand as it is.
I wonder if a guy could (carefully), use a hose on low to check for manifold vacuum leaks on a cold engine. I just use starting fluid, but nobody likes posting that because that can go so wrong. On a warm engine short shots will evaporate right away and not accumulate. IN any case you might see if any easy to reach bolts seem loose. If so you ramove the air cleaner and tighten them all, starting in the center and working out.
Also don't forget the power steering....And the EGR valve.
The IAC has a motor that is controlled by the ECU which sets the airflow through it, around the throttle plate. Unplugging it just leaves it set where it was.
The Vacuum ball, (and a check valve), holds vacuum for controls while the intake manifold vacuum crashes when you have your foot in it. A completely harmless cridder, that keeps your vents blowing right, your disco & light, and your cruse working.
09-26-2014, 04:28 PM
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my vacuum ball is gone, so ill replace that and I should have my cruise, vents and 4x4 light back right? I don't have the vac disco axle, is the light still triggered by vacuum? ill go around and tighten bolts. haven't checked the egr yet