TeKdo Posted May 14 Share Posted May 14 Hi guys, sorry to beat a dead horse but I really can't find any more tips on how to bring the idle down on the old girl. She's an '86 2.5 with an AX5 and idles right around 1300rpm. It idles just fine when its cold but as soon as it gets to operating temp (right around 200 *F on the gauge cluster) the idle bumps up to 1300rpm. It used to idle up at 1500rpm until i changed the coolant temp sensor (the one that goes to the ecu) and it dropped to 1300. So far I've -Fixed Vacuum Leaks -Tightened the manifold bolts -Replaced Coolant Temp Sensor (to ecu) -Done the Cruiser54 Ground Refresh (No Jeep Cables Kit though) -Checked TPS harness -Fiddled a bit with the TPS according to Cruiser's tips to see if the idle would drop after adjustment I've also tired to block off the vacuum port on the EGR valve to see if that was leaking since its new, that didn't change anything I've tried unplugging the Idle Speed Motor that pushes on the throttle to increase idle to see if that would bring the idle down (it didn't) Finally I've tried to adjust the TPS according to Cruiser's tips but I can't get a good back probe onto the senor's pigtail on my 2.5...there's fuel lines and a heater in the way. Pictures If it's worth noting, it still gets like 25 to 27 mpg with the high idle which really confuses me. I also don't have a working factory tach installed because it died years ago so I'm measuring the rpm with a new Equus 6088 that I picked up from O'reilly just so see if my ears were playing tricks on me so maybe the tach is out of wack or not accurate? Either way, I've run out of things that I could think of to replace outside of the TPS and possibly an O2 sensor and Idle Speed Motor. Both of those guys look a little worse for wear and I think my grandpa gave me a spare O2 sensor along with the truck too. I am worried about adjusting the TPS properly since i can't get my multimeter probes in there good. Dunno where I'd find a new Idle Speed Motor either...kinda wishing i had single barrel carb now or some kind of renix diag tool to see if a sensor is out of wack. Thanks for reading my little rant and any help is appreciated. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 14 Share Posted May 14 Have you adjusted the ISA at all? Did you buy the MJ from someone who was battling the same or similar issue? If that’s the case I suspect they adjusted the ISA when they shouldn’t have. That being said, unplugging the ISA won’t do anything. The ECU controls that. It should move back and forth to adjust the idle and at shut down it should go back into ready position to make the next start up easy. I have a whole DIY thread on how to adjust it by the AMC TBI service manual. Link to comment Share on other sites More sharing options...
Ωhm Posted May 14 Share Posted May 14 That vacuum cap has cracks in it. Could be a vacuum leak. Link to comment Share on other sites More sharing options...
TeKdo Posted May 14 Author Share Posted May 14 5 minutes ago, eaglescout526 said: Have you adjusted the ISA at all? Did you buy the MJ from someone who was battling the same or similar issue? If that’s the case I suspect they adjusted the ISA when they shouldn’t have. That being said, unplugging the ISA won’t do anything. The ECU controls that. It should move back and forth to adjust the idle and at shut down it should go back into ready position to make the next start up easy. I have a whole DIY thread on how to adjust it by the AMC TBI service manual. Thanks, I'll take a look into your thread. As far as for why this guy was parked, it was because the pinion bearing on the Dana 35 took a dump and the AX5 had expired as well. Plus my grandpa wanted to send it to a shop to get it fully restored at one point after he got T-Boned. As far as I know the ISA is the factory AMC one, he never used aftermarket parts when replacing something on this truck. I also don't think that the ISA has been really messed with honestly, it looks like the factory adjustment, but it looks wound all the way in already too. This is what the ISA looks like right now. Also thanks for the tip on the ISA. I thought it worked a little similar an IAC which is why I unplugged it to see if the idle would come down if the ECU wasn't telling it to open lol. Since the ISA is just for startup it works perfectly as well. Link to comment Share on other sites More sharing options...
TeKdo Posted May 14 Author Share Posted May 14 1 minute ago, Ωhm said: That vacuum cap has cracks in it. Could be a vacuum leak. Oh my gosh i completely missed that. If its that simple I'm gonna be a little upset with myself. Link to comment Share on other sites More sharing options...
TeKdo Posted May 14 Author Share Posted May 14 11 minutes ago, Ωhm said: That vacuum cap has cracks in it. Could be a vacuum leak. Well it dropped the RPM about another 50 to 100rpm...getting closer! I wonder if theres a couple other random vacuum caps or lines that I've missed now. Link to comment Share on other sites More sharing options...
Ωhm Posted May 14 Share Posted May 14 One more thing, that hose clamp looks like it missed it mark. Needs to move up the hose, could cause problems later down the road somewhere. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 14 Share Posted May 14 Ok if the ISA has never been touched then it’s more than likely vac leaks like Ωhm pointed out. That block at the base of the throttle body on 86’s are notorious for that. A TSB exists to replace that block with just straight vacuum lines to get rid of the problem all together. Link to comment Share on other sites More sharing options...
cruiser54 Posted May 15 Share Posted May 15 Link to comment Share on other sites More sharing options...
TeKdo Posted May 15 Author Share Posted May 15 18 hours ago, eaglescout526 said: Ok if the ISA has never been touched then it’s more than likely vac leaks like Ωhm pointed out. That block at the base of the throttle body on 86’s are notorious for that. A TSB exists to replace that block with just straight vacuum lines to get rid of the problem all together. Will look into doing that, I've been getting a little sketched out about that thing anyways. Haven't replaced it yet though, I didn't know you could replace it with just vac lines. Link to comment Share on other sites More sharing options...
TeKdo Posted May 15 Author Share Posted May 15 5 hours ago, cruiser54 said: are those holes on the right threaded for an NPT hose barb or does that rubber block thing just plug into there? Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 15 Share Posted May 15 15 minutes ago, TeKdo said: Will look into doing that, I've been getting a little sketched out about that thing anyways. Haven't replaced it yet though, I didn't know you could replace it with just vac lines. Yup. It’s a rubber block that honestly wasn’t great to begin with. Simple vac lines will do. The throttle body you’re looking at above is an 87-90 TB. It’s missing the other two ports that your 86 has. So don’t worry about that small detail. Link to comment Share on other sites More sharing options...
TeKdo Posted May 15 Author Share Posted May 15 4 hours ago, eaglescout526 said: Yup. It’s a rubber block that honestly wasn’t great to begin with. Simple vac lines will do. The throttle body you’re looking at above is an 87-90 TB. It’s missing the other two ports that your 86 has. So don’t worry about that small detail. Thank you for the help and insight! Will be replacing that block octopus thing with vac lines when i have a chance. Link to comment Share on other sites More sharing options...
TeKdo Posted May 15 Author Share Posted May 15 Update: The idle dropped down to 1100 outta nowhere. Took the Comanche for a little trip today because I needed a pickup truck. Did about an hour of highway driving, 60 - 70 miles an hour at ~2500rpm. Round trip was 86 miles total. When I left the house truck still idled at 1300 and now here we are at 1100. What the heck is going on. Could the EGR valve be partially stuck open with carbon and its slowly clearing up with long heat cycles? Link to comment Share on other sites More sharing options...
cruiser54 Posted May 16 Share Posted May 16 EGR can cause an undetectable vacuum leak. Link to comment Share on other sites More sharing options...
TeKdo Posted May 16 Author Share Posted May 16 18 hours ago, cruiser54 said: EGR can cause an undetectable vacuum leak. Would that explain why i can't find the vacuum leak by spraying starting fluid at all the vac connections? Link to comment Share on other sites More sharing options...
cruiser54 Posted May 16 Share Posted May 16 yep Link to comment Share on other sites More sharing options...
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