mik666 Posted March 21, 2016 Share Posted March 21, 2016 Hey Gang so my 87 4.0 w/ auto (pretty much stock) has developed a new occasional problem. Sometimes when i start it ,the idle is crazy high (not sure since i don't have a tach put i'm betting 3-4 K). If i shut it off and restart it it will be fine -(took 3 shut offs/restarts today before was fine). It really just started this after i replaced the battery about a week ago - i'm not sure if that has anything to do with it but it never happened before hand. I've done most of cruisers tips before hand (except getting rid of the big ole connector job), the CPS and most everything electrical has been replaced ( coil, points, oxy sensor, etc). i even put a new computer control module thing in to try and squeeze the extra HP out the ole thing - never done it till recently... anyway anyone have anything they can point me too? i unplugged the battery and let it sit for a while but it still will occasionally do this ... thx! mik Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted March 21, 2016 Share Posted March 21, 2016 Remove and clean throttle body until you would be ok eating out of it. Clean IAC valve and port too. Adjust TPS according to Cruisers tips, if problem persists you may need to replace either the TPS or IAC. FPC. Link to comment Share on other sites More sharing options...
Fsjcherokee Posted March 21, 2016 Share Posted March 21, 2016 Didnt earlier models suffer from manifolds bolts loosening up? May want to tighten them up. Link to comment Share on other sites More sharing options...
cruiser54 Posted March 21, 2016 Share Posted March 21, 2016 Remove and clean throttle body until you would be ok eating out of it. Clean IAC valve and port too. Adjust TPS according to Cruisers tips, if problem persists you may need to replace either the TPS or IAC. FPC. This^^^. Link to comment Share on other sites More sharing options...
Eagle Posted March 21, 2016 Share Posted March 21, 2016 High idle on the Renix 4.0Ls is usually caused by a dirty IAC, but there's another possibility, also. The throttle cable from the pedal through the firewall leads to a bellcrank assembly mounted down on the driver's side frame rail. From that bellcrank, there's a rigid arm that goes up to move the throttle plate. The pivot of that bellcrank assembly can get gunked up and/or rusted, and resist allowing the throttle to close fully at idle. On my '88 XJ I've had to hose it down with PB Blaster a few times to free it up. Link to comment Share on other sites More sharing options...
onlyinajeep726 Posted March 21, 2016 Share Posted March 21, 2016 Mine was manifold bolts. Tighten them with the strength of Thor and also do the aforementioned suggestions with the TB, IAC, etc. Link to comment Share on other sites More sharing options...
mik666 Posted March 21, 2016 Author Share Posted March 21, 2016 OK cool thx guys i'll go through the suggestions this week and report back! Link to comment Share on other sites More sharing options...
mik666 Posted March 25, 2016 Author Share Posted March 25, 2016 replaced the "new-ish" IAC valve with the old one (scrubbed w/ electrical cleaner and soft brush, good thing i'm a packrat ) and the MJ has been good for 4 days now - you guys rule! thx! mike Link to comment Share on other sites More sharing options...
cruiser54 Posted March 26, 2016 Share Posted March 26, 2016 replaced the "new-ish" IAC valve with the old one (scrubbed w/ electrical cleaner and soft brush, good thing i'm a packrat ) and the MJ has been good for 4 days now - you guys rule! thx! mike I'm thinking that nowadays a refurbished factory part is way better than a new POS part. Link to comment Share on other sites More sharing options...
Rockfrog Posted March 26, 2016 Share Posted March 26, 2016 Agreed, I try to keep all the factory sensors I can find. It's also how I happened on the GM 2.8L TPS compatible swap for manuals ... It just looked too familiar to toss. Link to comment Share on other sites More sharing options...
mik666 Posted April 8, 2016 Author Share Posted April 8, 2016 Damn it the high idle has returned, took 3 shut offs this morning and then unplugging the cps while it was running (dies of course) to get the idle low again. i cleaned the throttle body, tightened the throttle body bolts (they were pretty tight), lube up all the linkage on the throttle body/cable, checked the CPS setting - spot on - idled nice then after work did the high idle again, but after 1 restart was fine - damn thing . I have an extra CPS i'll put in on the weekend - but not sure if this is but i'll try it - also going to remove the IAC and scrub it again but it was clean as a whistle when i changed it out - any other suggestions guys? thx! mike Link to comment Share on other sites More sharing options...
cruiser54 Posted April 8, 2016 Share Posted April 8, 2016 Damn it the high idle has returned, took 3 shut offs this morning and then unplugging the cps while it was running (dies of course) to get the idle low again. i cleaned the throttle body, tightened the throttle body bolts (they were pretty tight), lube up all the linkage on the throttle body/cable, checked the CPS setting - spot on - idled nice then after work did the high idle again, but after 1 restart was fine - damn thing . I have an extra CPS i'll put in on the weekend - but not sure if this is but i'll try it - also going to remove the IAC and scrub it again but it was clean as a whistle when i changed it out - any other suggestions guys? thx! mike CPS or TPS? What are you setting your TPS to? Link to comment Share on other sites More sharing options...
mik666 Posted April 8, 2016 Author Share Posted April 8, 2016 Hey Cruiser - woops meant TPS (6 am and to many beers last night) - set as in your tips, don't remember exactly the setting but got it spot on. like i said i have another one thats new in the box i'll change out this weekend thx! mike Link to comment Share on other sites More sharing options...
cruiser54 Posted April 8, 2016 Share Posted April 8, 2016 I figured. LOL. It's probably bad. Link to comment Share on other sites More sharing options...
mik666 Posted April 8, 2016 Author Share Posted April 8, 2016 OK so new TPS in, adjusted as per cruisers tips. start the bastard and the idle shoots right up - damn , restart again and again to no avail, finally i unplug the IAC and the idle drops right away. So pulled the replacement IAC out of the box that i initially changed out in the beginning of this saga and replaced the one that was in the engine (weird the piston on the one in the jeep was fully extended). start it, idle is fine,..... for now WTF so anyways i think it must be an IAC issue - anyone know it there is a real mopar IAC available (part number??) thx as always mike Link to comment Share on other sites More sharing options...
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