88-mj-petersen Posted February 24, 2014 Share Posted February 24, 2014 I got a 88 cheif 4.0 manual 4x4. Has a bit of a high idle(anywere betweer 1000 and 1250) and ita random, hot or cold but mostly hot. Iv replaced the vaccum harness, replaced IAC, cleaned throttle body, set the tps cleaned the c101, cleaned the ground on the dip stick and on the firewall, replaced 1 factory crimp going to the c101. Maybe a few things i forgot The battery ground is on the dip stick stud but I'm wouldnt think that would make a diffrence. I'm thinking its t maybe a bad intake gasket. Is there a way to test that without spraying carb cleaner or anything everywere? Or any other ideas on what to check? Link to comment Share on other sites More sharing options...
88-mj-petersen Posted February 24, 2014 Author Share Posted February 24, 2014 Forgot to add. Iv done a full tune up about 4000 miles or less ago( plugs,wires,cap,rotor,fuel filter, and air filter). Also replaced the fuel pressure regulator and cleaned the fuel pump ground behind the tail light. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 24, 2014 Share Posted February 24, 2014 Carb cleaner works quite well. have you snugged up the intake manifold bolts? Has someone, sometime messed with the throttle butterfly stop screw? How did you adjust the TPS and which plug did you use, flat or square? Link to comment Share on other sites More sharing options...
ParadiseMJ Posted February 24, 2014 Share Posted February 24, 2014 1. When the truck is cold, put a wrench on your manifold bolts and try to cinch them up . 2. Other than a very careful visual of the vac system or spraying carb cleaner etc. you might want to have it smoke tested. 3. Check the other connections at the manifold. 4. Double check brake booster hose. Link to comment Share on other sites More sharing options...
Pete M Posted February 24, 2014 Share Posted February 24, 2014 an unlit propane torch works in lieu of carb cleaner. :thumbsup: Link to comment Share on other sites More sharing options...
64 Cheyenne Posted February 24, 2014 Share Posted February 24, 2014 Get a cigar blow smoke into vacuum lines, see where it comes out (smoke) Link to comment Share on other sites More sharing options...
88-mj-petersen Posted February 24, 2014 Author Share Posted February 24, 2014 I did check the manifold bolts once befor but if i remember right i did it with the truck hot. I havnt touched the butterfly stop screw but i could check to be sure that it is were it needs to be. Setting the tps i took voltage from the flat one. Probed A and B got about 4.90. So i probed B and C and set it about 0.84. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 24, 2014 Share Posted February 24, 2014 I did check the manifold bolts once befor but if i remember right i did it with the truck hot. I havnt touched the butterfly stop screw but i could check to be sure that it is were it needs to be. Setting the tps i took voltage from the flat one. Probed A and B got about 4.90. So i probed B and C and set it about 0.84. Did you ever do the sensor ground test? Cruiser’s Renix Sensor Ground Test This sensor ground circuit affects the CTS, TPS, IAT, MAP, ECU and diagnostic connector grounds. It’s very important and not something to overlook in diagnosing your Renix Jeep as it is common for the harnesses to have poor crimps causing poor grounds. If any or all of the sensors do not have a good ground, the signal the ECU receives from these sensors is inaccurate. Set your meter to measure Ohms. Be sure the key is in the OFF position. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself. Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too. You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well. Revised 06/12/2012 Link to comment Share on other sites More sharing options...
88-mj-petersen Posted February 24, 2014 Author Share Posted February 24, 2014 I did do that. Thats how i found the bad crimp in the harness going into the c101. Link to comment Share on other sites More sharing options...
88-mj-petersen Posted February 24, 2014 Author Share Posted February 24, 2014 I didnt wiggle the harness going behind the map sensor on the firewall tho. Completely forgot about that one. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 24, 2014 Share Posted February 24, 2014 So it's all still good? I'm rapidly approaching becoming an advocate for C101 elimination. Try shooting for .82 or .83 on your TPS setting. Link to comment Share on other sites More sharing options...
88-mj-petersen Posted February 24, 2014 Author Share Posted February 24, 2014 But yes ot checked out ok. I was thinking about eliminating the c101 but I'm not sure at this time. I will set the tps about 0.82 and let you kno what happens. Could that small of a change in voltage make it idle the way it is? Link to comment Share on other sites More sharing options...
cruiser54 Posted February 24, 2014 Share Posted February 24, 2014 Possibly. Is it consistently doing this or just sometimes upon start-up? Link to comment Share on other sites More sharing options...
88-mj-petersen Posted February 24, 2014 Author Share Posted February 24, 2014 Well on start up it will rev to about 2000 but drop right back down right away(i though it might be normal since the girlfriends 92 cherokee does it as well) but otherwise its kind of random. Sometime it will run fine and sometime it will idle high. Mostly acts up when the engine is warm tho. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 24, 2014 Share Posted February 24, 2014 Reset the TPS. GF's 92 is a different animal altogether. Link to comment Share on other sites More sharing options...
88-mj-petersen Posted February 24, 2014 Author Share Posted February 24, 2014 Ok i will do that and let you kno Link to comment Share on other sites More sharing options...
88-mj-petersen Posted March 3, 2014 Author Share Posted March 3, 2014 Reset the tsp and its about the same. Tooks the throttle body off and cleaned it out again to make sure and reset the tps and still didnt help. Tried spraying carb cleaner around the intake, vacuum harness and throttle body and the idle didnt change any. My plugs are turning white to. I beleive that means it running to lean? Link to comment Share on other sites More sharing options...
cruiser54 Posted March 3, 2014 Share Posted March 3, 2014 I did my first C101 elimination last week on my neighbor's 87. Real easy. We soldered and used shrink tubing. One wire at a time. Link to comment Share on other sites More sharing options...
88-mj-petersen Posted March 3, 2014 Author Share Posted March 3, 2014 That was my next thought. Thanks for all your help so far. Link to comment Share on other sites More sharing options...
cruiser54 Posted March 3, 2014 Share Posted March 3, 2014 That was my next thought. Thanks for all your help so far. What got me leaning towards that is when my buddy bypassed the C101 with his cPS wires, then the sensor grounds. Had an odd cold running issue. We hooked up my factory tester and monitored the sensors. The CTS looked fine until he barely wiggled the C101 and the reading went to hell. I have some photos but I'm too much of a dumbass to post them here. Link to comment Share on other sites More sharing options...
88-mj-petersen Posted March 4, 2014 Author Share Posted March 4, 2014 Well its probably something i will get at this weekend. I'm going to clean the c101 again and test the sensor grounds in case i missed something and see what happens. But i think I'm going to bypass that either way. Link to comment Share on other sites More sharing options...
cruiser54 Posted March 4, 2014 Share Posted March 4, 2014 Know how to post photos on here? Link to comment Share on other sites More sharing options...
88-mj-petersen Posted March 4, 2014 Author Share Posted March 4, 2014 No. can't really figure that part out Link to comment Share on other sites More sharing options...
cruiser54 Posted March 4, 2014 Share Posted March 4, 2014 No. can't really figure that part out Need or want some C101 elimination photos? Link to comment Share on other sites More sharing options...
88whitemanche Posted March 4, 2014 Share Posted March 4, 2014 Know how to post photos on here? Cruiser so you have by any chance have a write up on this c101 bypass? Link to comment Share on other sites More sharing options...
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