NC Tom Posted October 13, 2017 Share Posted October 13, 2017 I've been reading through the many, many posts on fixing the high idle at start-up. I was hoping that if I post my specific issues, the pros here could help narrow it down. It's been doing it off and on for a while now. I mean around four months. Started quite suddenly after getting a new muffler. I have no CAT, but don't think it's related because the CAT was already bad. When it was doing it, if I drove a bit, it would calm down. However, maybe three weeks ago, it didn't calm down. Was high, and a bit scary, on my 20 minute commute home. It was like having cruise set to 25 MPH non-stop! Has not acted up again until this morning. I tried to shut-off and restart to get it to quit, but no luck. After about three tries, it would turn but not start. Can you flood a fuel-injected engine? Had to take the wife's car. Anyway, guess I'll check it again this evening. So, based on that story, anybody have any ideas where to start. I know there can be several pieces to this puzzle. Thanks. Link to comment Share on other sites More sharing options...
HOrnbrod Posted October 13, 2017 Share Posted October 13, 2017 https://comancheclub.com/forums/topic/51707-cc-members-create-a-signature-to-describe-your-mj/ Link to comment Share on other sites More sharing options...
kryptronic Posted October 14, 2017 Share Posted October 14, 2017 HOrnbrod's got a good point. We have no idea what type of MJ you have. Renix or HO? What to look for to diagnose your issue is going to be highly dependent on the engine and electronics you have. Link to comment Share on other sites More sharing options...
NC Tom Posted October 14, 2017 Author Share Posted October 14, 2017 Renix I6 Link to comment Share on other sites More sharing options...
cruiser54 Posted October 14, 2017 Share Posted October 14, 2017 Okay. Thanks. Your Throttle Position Sensor is likely bad. Can we squeeze the YEAR out of you also so we can be more specific addressing your issues? Go to www.cruiser54.com and complete Tips 1 through 5 before doing anything else. Link to comment Share on other sites More sharing options...
Comavalanche Posted October 14, 2017 Share Posted October 14, 2017 18 minutes ago, cruiser54 said: Okay. Thanks. Your Throttle Position Sensor is likely bad. Can we squeeze the YEAR out of you also so we can be more specific addressing your issues? Go to www.cruiser54.com and complete Tips 1 through 5 before doing anything else. Had the same issue on my 88. The TPS was giving a reading on my REM that the throttle was partially open even when the truck was at idle. I noticed a ground wire that was frayed and exposed. Wrapped it with heat shrink and it fixed it. Also sprayed brake clean on my throttle cable and linkages for good measure. Do cruisers tips before you waste any money. Ask me how I know..... Link to comment Share on other sites More sharing options...
NC Tom Posted October 14, 2017 Author Share Posted October 14, 2017 2 hours ago, cruiser54 said: Okay. Thanks. Your Throttle Position Sensor is likely bad. Can we squeeze the YEAR out of you also so we can be more specific addressing your issues? Go to www.cruiser54.com and complete Tips 1 through 5 before doing anything else. "88 Comanche Pioneer Renix, I6, Auto, 4WD 200K+ miles" I don't know where to put the model info in my profile. I was thinking TPS too. I'm really squeezed for time to do any trouble-shooting currently. It doesn't help that I don't have a garage. Wondering if TPS can just be replaced now and trouble-shoot, in a few weeks? Link to comment Share on other sites More sharing options...
SVPete Posted October 15, 2017 Share Posted October 15, 2017 8 hours ago, NC Tom said: I don't know where to put the model info in my profile. Instructions are pinned on the first page of this forum..... CC Members - Create a Signature to Describe Your MJ Link to comment Share on other sites More sharing options...
cruiser54 Posted October 15, 2017 Share Posted October 15, 2017 20 hours ago, NC Tom said: "88 Comanche Pioneer Renix, I6, Auto, 4WD 200K+ miles" I don't know where to put the model info in my profile. I was thinking TPS too. I'm really squeezed for time to do any trouble-shooting currently. It doesn't help that I don't have a garage. Wondering if TPS can just be replaced now and trouble-shoot, in a few weeks? If you chuck a new TPS on there and don't adjust it properly and/or don't address the grounds, you have accomplished nothing. Link to comment Share on other sites More sharing options...
NC Tom Posted October 15, 2017 Author Share Posted October 15, 2017 3 hours ago, cruiser54 said: If you chuck a new TPS on there and don't adjust it properly and/or don't address the grounds, you have accomplished nothing. I figured you say that. Well, guess I'll be dealing with it for a while longer, unless the TPS can be cleaned or tapped-on or some other bandaid. Link to comment Share on other sites More sharing options...
cruiser54 Posted October 15, 2017 Share Posted October 15, 2017 It might not BE the TPS!!!! Do the Tips. Takes little time. Link to comment Share on other sites More sharing options...
NC Tom Posted October 15, 2017 Author Share Posted October 15, 2017 16 hours ago, SVPete said: Instructions are pinned on the first page of this forum..... CC Members - Create a Signature to Describe Your MJ Link to comment Share on other sites More sharing options...
NC Tom Posted October 15, 2017 Author Share Posted October 15, 2017 17 minutes ago, cruiser54 said: It might not BE the TPS!!!! Do the Tips. Takes little time. Yeah, yeah, I know. Link to comment Share on other sites More sharing options...
metrictonner Posted October 15, 2017 Share Posted October 15, 2017 Not having any knowledge of what you drive, check my MJ and if it is near matching I have a couple of suggestions because I just fixed my high idle problem today and my problem sounds exactly like yours. 1. While a TPS should be adjusted correctly, an improperly adjusted one actually lowers my idle causing stalling problems. For some reason my DRBII sets the TPS voltage differential to 13% rather than the Renix manual 17%. So what is right? The 13% actually masked a sticky IAC problem. 2. My problem was a sticky IAC. The stepper motor innards were sticky, not the throttle body mounting. These things cannot be fixed so you must buy a new one. Much has been said on this board about how many IACs people have been through until they finally find one that works. I broke down and bought a $60+ one to replace a $40 one that lasted about a year. I think the $60 one is performing better than the $40 one when new. 3. The usual complaint about china parts can also mean that parts that appear to work when new may need to be replaced sooner than expected and regularly...the joy of owning an antique vehicle for which there are no OEM parts any more. You can test for IAC sticking by removing the air intake from the throttle body. With the engine roaring away, slide your finger up onto the throttle body bypass air duct that the IAC uses. If the idle RPM lowers as you slide your finger over the duct you have a sticky IAC. You can also check to make sure the throttle body butterfly is closed at idle. Good luck. Link to comment Share on other sites More sharing options...
SVPete Posted October 17, 2017 Share Posted October 17, 2017 (edited) Too early to call it fixed......? I too have been experiencing a high idle periodically on start up and sometimes the idle would seem (audibly) high when I would pull up to a light or stop sign. I worked through / checked a lot of things including many of Cruisers tips. I was just enduring it since I hadn't figured it out. For some reason on Saturday, I pulled the Manifold Air Temperature sensor out again and cleaned the crap out of it. I had done that previously, but I'll say it was a "good enough" cleaning (considering what it looked like before, all mucked up). This time I used degreaser and a pipe cleaner and made the thermistor inside shine since it still had baked on brown stuff on it. So far, for 2 1/2 days, it has made a difference. No extremely high revs on start up and the engine is audibly idling lower as I am driving. This doesn't mean it is the magic bullet. Certainly work through Cruisers tips, but add this to the list if you haven't removed and cleaned it......really well. And remember to clean the contacts in every electrical connector you disconnect. Edited October 22, 2017 by SVPete Came back after changing the oil of all things...... Link to comment Share on other sites More sharing options...
Gubachoo Posted October 22, 2017 Share Posted October 22, 2017 Another vote in favor of something linked to the TPS. I had similar problems so I cleaned the grounds for mine, checked it with a meter, installed the new one, and clocked it properly, and if you don't include the trip to the parts store, it took, in all, maybe 30 mins. That cruiser guy knows what he's saying. ☺ Link to comment Share on other sites More sharing options...
NC Tom Posted November 17, 2017 Author Share Posted November 17, 2017 On 10/14/2017 at 10:05 AM, cruiser54 said: Okay. Thanks. Your Throttle Position Sensor is likely bad. Can we squeeze the YEAR out of you also so we can be more specific addressing your issues? Go to www.cruiser54.com and complete Tips 1 through 5 before doing anything else. Well, I never have been good at following directions, so I skipped to item 11. My throttle body was a black, crusty mess. I gave it a Seafoam cleaning and it does run better. The high idle is mostly resolved. I will go back and do tips 1-5. I thought I would just throw these current symptoms out there. From a cold start, the high idle is gone. From a hot start, it's a crap-shoot, but when I get the high idle it calms down after a bit. The idle increases some when moving auto shifter to Park. Link to comment Share on other sites More sharing options...
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