Engine Idle & Tps Adjustment Help Request

Discussion in 'Fox 5.0 Mustang Tech' started by Skyler Wilson, Mar 9, 2014.


  1. Skyler Wilson

    Skyler Wilson Member

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    Hello everyone i'm new to the forums with a 1989 5.o GT 25th Anniversary model i recently picked up and this looks like the perfect community to join for what i'm looking for. I'm having issues as far as the engine running a bit lean, idle and deceleration of the throttle; mostly when in neutral or revving with the clutch engaged. It climbs down extremely slowly and has a running idle of 1600 rpm's while in neutral and 1400-1500 rpm's with the clutch engaged in gear. So far i have removed the throttle body and all components except the TPS for cleaning and i have replaced the EGR and IAC with all new gaskets. I have also ran it without the IAC valve plugged in and i get a better idle; around 1200-1300 rpm's and a way better throttle response as far as deceleration. Now for the fact that the IAC is brand new, the throttle body is nice and clean and it has all new gaskets i'm gonna assume the problem lies somewhere else. So my questions are the following: What in the chain here could cause this slow deceleration issue, Does my idle need to be adjusted or is something out of adjustment that makes it idle high and what should the idle be on this particular stang? TPS have anything to do with running lean and higher idle? Any help would be greatly appreciated!

    Also as far as what i know, its equipped with an aftermarket cam of some sort, distributor, oil pump, edlebrock intake manifold & throttle body that i believe is a 65mm bore. I'm not sure exactly if being a bit more high performance effects what a base idle should be or not so i guess i'll throw that in there.
     
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    Last edited: Mar 9, 2014
  2. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. :D

    It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 134,000 hits, which indicates it does help fix idle problems quickly and inexpensively.
     
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  3. Noobz347

    Noobz347 Stangnet Facilities Maint Tech... Er... Janitor Admin Dude

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    This needs to be a sticky... At least for a little while. :nice:
     
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  4. Skyler Wilson

    Skyler Wilson Member

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    I didn't see the checklist till after i posted this but just in the course of a day or so i have pretty much dialed out my idle problems from adjusting the TPS and adjusting the throttle plate from the guidelines off the checklist. I still have a surging problem when the motor gets up to temp but i'm starting to think it has to do with an under the hood cold air intake & filter that is aimed towards the header and seems to get really hot. Definitely a very helpful list of things to check.
     
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  5. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Seems like you have a HOT air intake instead of a cold air intake. :D
     
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  6. JonezySN95

    JonezySN95 Member

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    My money is on a vacuum leak. Go out and buy a can of carb cleaner, while it's idling spray a few areas where there is gaskets between the MAF all the way to your heads (ie: TB gasket, intake manifold gasket, ect.) and listen for a rise in rpm. This would also explain why it's running lean. Hope this helps, good luck.
     
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  7. Gearbanger 101

    Gearbanger 101 Straight Outta Locash Super Mod

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    I concur.
     
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  8. skiwesser11

    skiwesser11 Member

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    I am getting a page not found error on this link?? Could you please repost??
     
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