Jump to content

Help! High Idle (Done multiple searches already)


Recommended Posts

I am having a huge conundrum. I am having issues with a high idle on my 89 Comanche. At the moment when I idling it bounces/surges between 1200-1400 rpm. When I say surges,I mean constantly, within 1-2 second intervals it will surge between that predescribed rpm. I cannot for the life of me get it to hold a steady idle nor get the idle down below 1000. To this point I have followed everyone of cruiser54's tips for the renix. I have refreshed all my grounds, cleaned the throttle body, cleaned, then accidentally broke, thus subsequently replaced the iac, tested the tps (was within spec),adjusted the butterfly, replaced the O2 sensor, and tightened all of the intake/manifold bolts. To date I have not cleaned the ECU contacts. Now this is to get a second opinion on my train of thought and next plan of action. I noticed the rpm went up when I changed out the OEM aluminum valve cover to a steel one from a 99-00 jeep Cherokee. I swapped this out as I had read that others had done this to eliminate the issue of oil blow by getting onto the air filter. Everything I read and researched, no one had issues with a high idle post swap. I know that on the older valve cover the rear CCV line acts a restrictor reducing the vacuum pressure. This leads to it becoming gunned, causing the gases to escape into the air filter instead of the manifold. On the steel one the PCV line is now putting direct vacuum on the valve cover.

 

I threw the old valve cover out, should I concede defeat and track down an original valve cover and swap it back out. Any thoughts, suggestions, or opinions are greatly appreciated.

Link to comment
Share on other sites

On the rear of the valve covers there is an elbow that goes to the intake manifold. It gets vacuum to pull out gasses caused during combustion. The original renix set-up uses a metered line (small inner diameter) to limit the amount of air that can pass through. The stamped steel VC uses a metered orifice. What kind of combo / set-up do you have? My thought is that if nothing is metered (large elbow at the rear of the VC and large line from the elbow to the intake) you could be getting large amounts of air to pull directly into the intake causing high idle.

Link to comment
Share on other sites

On the rear of the valve covers there is an elbow that goes to the intake manifold. It gets vacuum to pull out gasses caused during combustion. The original renix set-up uses a metered line (small inner diameter) to limit the amount of air that can pass through. The stamped steel VC uses a metered orifice. What kind of combo / set-up do you have? My thought is that if nothing is metered (large elbow at the rear of the VC and large line from the elbow to the intake) you could be getting large amounts of air to pull directly into the intake causing high idle.

Exactly.

Link to comment
Share on other sites

Okay I am on the same page now. It is/should be the metered OEM elbow for the steel valve cover if I purchased the correct part, since now talking with you guys I am not sure if I did purchase it, as if I had it I probably would not be having high idle issues related to this. I believe it is either a Dorman - Crankcase Vent Tube, part number RBA47057 or Crown Automotive - PCV Valve, Part Number 53030495.

Link to comment
Share on other sites

Not a stupid thought, very valid. I may have possibly done that. I will have to look into that. I'll get back to you guys if that wasn't the issue, it'll be a while before I have time, and the parts to check the elbows.

Link to comment
Share on other sites

  • 2 weeks later...

So I checked a found that I had mixed PCV the elbows up. I put the appropriate elbow (the one with the restrictor) on the rear of the valve cover. Upon complete the swap, when starting the jeep it retained the high, pulsating idle. When it was running I was playing around with the wiring harness and unplugged the vacuum line from the MAP sensor, the idle on the jeep instantly dropped to 800 rpm and held steady. When I would reconnect the vacuum line to the MAP sensor the idle would shoot back up to 1200 rpm and begin to pulsate like originally. Would/could a bad MAP sensor cause this symptom?

Link to comment
Share on other sites

Your tips that can be considered the renix bible. Ever since purchasing my jeep I have referenced your tips, to date they have not steered me wrong.  I have refreshed all my grounds, cleaned the throttle body, cleaned, then accidentally broke, thus subsequently replaced the iac, tested the tps (was within spec),adjusted the butterfly, replaced the O2 sensor, and tightened all of the intake/manifold bolts. To date I have not cleaned the ECU contacts or messed with the butterfly adjustment screw. When reading your tips and post in various forums when helping others, messing with the adjustment screw is a big no. So I have not messed with it, waiting until it becomes a last resort. I found a old post on cherokee forum from 2011, where a guy was hae the exact same problems that I am having (you were helping him) and he ended up adjusted the butterfly screw. Here is the link for reference http://www.cherokeeforum.com/f2/renix-high-idle-still-106800/index5/

 

 

About an hour ago after reading the posts I went and checked the butterfly adjustment screw and noticed a previous owner had tampered with it. The bolt was stripped and it appears that they used pliers to move it.

.

 

From the picture below is this opening on the butterfly to much?

Link to comment
Share on other sites

That's open rather far. Got a set of feeler gauges that go down to .003"?

I noticed I had a typo in my last post, to date I have not touched the butterfly even though I said I had. I don't own any feeler gauges at the moment, but I can own a set here soon. 0.003, is that how open I want my butterfly to be?

 

 

Hit and miss engine technology. Gotta love it...............

 

220px-Amanco_hit-and-miss_engine%28GDSF_

It has been a joy chasing this mystery down (thats thick with sarcasm). Although the one good thing is I have become very familiar with mulitple systems of my jeep I otherwise would have ignored.

Link to comment
Share on other sites

 

That's open rather far. Got a set of feeler gauges that go down to .003"?

I noticed I had a typo in my last post, to date I have not touched the butterfly even though I said I had. I don't own any feeler gauges at the moment, but I can own a set here soon. 0.003, is that how open I want my butterfly to be?

 

 

Hit and miss engine technology. Gotta love it...............

 

220px-Amanco_hit-and-miss_engine%28GDSF_

It has been a joy chasing this mystery down (thats thick with sarcasm). Although the one good thing is I have become very familiar with mulitple systems of my jeep I otherwise would have ignored.

 

Education is a journey.........

Link to comment
Share on other sites

Okay, made a stop at the auto parts store to purchase a set of feeler gauges that go down .003, also purchased a new throttle body gasket while I was there. Using Cruiser54's renix tip #14 adjusting the butterfly screw I closed the gap between the throttle body wall and butterfly. Try as I might I could not get the allen wrench to turn, in the end I had to use some vice grips to grip the screw and turn in it. I went until I could barely slide the .003 feeler gauge between the wall and butterfly, here is what it looks like now.

 

Correct me if I am wrong, I recall reading somewhere that you want only the faintest of light getting through, after adjusting it I shone a flashlight through to verify.

 

As of right now it appears that adjusting the butterfly has solved my high idle issue. I started it and the idle was between 600-800 rpm. I let it sit and idle to half of operating temperature and it never climbed above 800 rpm. I will give it a good test drive tomorrow to see how it the idle behaves once it gets to operating temperature. Still can't get the idle to stop pulsating in the 200 rpm range. But as of right now I am considering this a small victory. Thanks to everyone that has helped me with this issue, if tomorrows drive proves its not fixed, I know where to come to continue trouble shooting.

Link to comment
Share on other sites

I'm curious about the clearance between the butterfly and housing. How did you come up with yours? 

Should the clearance be different, if it is not correct I'd like to know. I would rather go back and fix it correctly and be done with it than have a band-aide fix and have it evolve into a bigger issue donw the road.

 

I arrived at the clearance that I have right now through a number of factors, First, using your renix tip for adjusting the butterfly, I know in the post you never give any space measurements, it simply states close all the way and open until the faintest movement is detected. Second in a previous post you made on this thread you asked if I had a set of feeler gauges that go down to 0.003", in response to that post I asked if that is the gap measurement that I neede, you must have missed the question, you never responded to that one. And finally reading through mulitple forums on adjusting the butterfly (most seemed to treat it as a quick easy fix to idle problems), with the knlowdege the butterfly needs to be open as minimally as possibly I recall reading a post that you want only the faintest of light getting through.

Link to comment
Share on other sites

We're working on a dimension that will work. There is no factory dimension.

 

In theory, that stop screw is just that, to keep the butterfly from gouging the throttle bore.

 

Mcgowan came up with the .003" clearance. Please try it and let us know. 

Link to comment
Share on other sites

Okay, well it is currently set with the clearance of .003". I adjusted until I could barely (not having to force) slide the .003" feeler gauge between the wall and butterfly. Thus far it has been working great, my idle is down to 600 rpm at start up and when at operating temperature, adjusting the butterfly has resolved my issue. The PO must have adjusted the stop screw as a quick easy fix to an idle issue and never addressed the real issue. Then at some point in my repairing and replacing old worn out parts, I must have addressed the underlying issue and his band-aide fix was brought to light. Again thanks to all who have given help and input in this issue.

Link to comment
Share on other sites

Okay, well it is currently set with the clearance of .003". I adjusted until I could barely (not having to force) slide the .003" feeler gauge between the wall and butterfly. Thus far it has been working great, my idle is down to 600 rpm at start up and when at operating temperature, adjusting the butterfly has resolved my issue. The PO must have adjusted the stop screw as a quick easy fix to an idle issue and never addressed the real issue. Then at some point in my repairing and replacing old worn out parts, I must have addressed the underlying issue and his band-aide fix was brought to light. Again thanks to all who have given help and input in this issue.

I think progress is being made!!!

Link to comment
Share on other sites

Very intesting thread...  sounds like someone had a stuck IAC valve, and set idle with the stop screw instead...  You created a fast idle then when you put the unrestricted elbow on the large PCV vacuum line, basically allowing it to suck WAY more air than it should have.   Then you replaced the stuck IAC valve with a new one, but it still wasn't able to lower the idle becasue of the stop screw being too far out, and the PCV elbow in the wrong place...  You've fixed those issues, and now idle speed is correct, but it's still surging...

 

It's entirely possibly that you got a bad IAC valve...   A sticky one will cause surging.  If you've already tried plugging all the vacuum ports at the manifold, one at a time to see if the surging goes away with one of them plugged, then you might try taking the IAC out and getting another one.  More and more I find that the replacement parts we're getting from the big auto parts stores, even with name brands sometimes, are junk.

 

YMMV.

Chris

Link to comment
Share on other sites

  • 2 weeks later...
  • 1 month later...

Very intesting thread...  sounds like someone had a stuck IAC valve, and set idle with the stop screw instead...  You created a fast idle then when you put the unrestricted elbow on the large PCV vacuum line, basically allowing it to suck WAY more air than it should have.   Then you replaced the stuck IAC valve with a new one, but it still wasn't able to lower the idle becasue of the stop screw being too far out, and the PCV elbow in the wrong place...  You've fixed those issues, and now idle speed is correct, but it's still surging...

 

It's entirely possibly that you got a bad IAC valve...   A sticky one will cause surging.  If you've already tried plugging all the vacuum ports at the manifold, one at a time to see if the surging goes away with one of them plugged, then you might try taking the IAC out and getting another one.  More and more I find that the replacement parts we're getting from the big auto parts stores, even with name brands sometimes, are junk.

 

YMMV.

Chris

 

 

About every 75,000 my Comanche starts idling 1500-2000 rpm. A new TPS has fixed it each time, I'm on the 3rd or 4th one now.

 

Thanks for the suggestions, I think I will try both of your guys suggestions at some point in the near future. I am still enjoying the fact that it has a normal idle.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...