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2.3L ('83-'97) Low rough idle…no CEL


OldMan89

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Started my Dailey up the other day and everything seemed normal. Drove around 10 miles and stopped at a stop light and it was idling rough around 650-700. Took off and all was normal. Made it to a longer light and after a few minutes it dropped to 500-550 and ran really really roughy but it accelerated fine. Now it startes fine, runs fine, and drives fine. Just idles low and after being stopped for a minute it drops even lower…..I ran a small amount some barrymans in a half tank of fuel a few days before this and topped off the tank today. I’ve replaced the iac a while back but not with a motor craft. Still have my OG but it needs a deep clean. Tapped on egr while running but nothing changed. Tapped on iac but nothing changed. Checked for vacuum leaks with starting fluid and no surges of any kind. So I’m a little stumped. Can anyone point me in the right direction?
 


scotts90ranger

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to eliminate the IAC, unplug it with the engine running, it should go down to that 500ish rpm range, if it stalls then it's something else. An '89 doesn't have much for diagnostics, don't think there's even an EGR position sensor (think that came in in '90), wouldn't care about a vacuum leak but you have the opposite issue, doesn't sound like spark, it would care about running rich which could cause a low idle... I'd expect IAC to be most likely.
 

OldMan89

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to eliminate the IAC, unplug it with the engine running, it should go down to that 500ish rpm range, if it stalls then it's something else. An '89 doesn't have much for diagnostics, don't think there's even an EGR position sensor (think that came in in '90), wouldn't care about a vacuum leak but you have the opposite issue, doesn't sound like spark, it would care about running rich which could cause a low idle... I'd expect IAC to be most likely.
Definitely think it is running rich. I unplugged the iac and it really made no change. Mabey a little bit. I know I need to replace my temp sensor which I have read can make one run rich. I have it and plan on putting that in this weekend.
 

scotts90ranger

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If unplugging the IAC doesn't change anything that means the IAC isn't opening
 

OldMan89

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Cleaned my OEM iac and put it back in place of the failed unit and it helped for a few minutes. But still idling low and will stumble pretty good when I press the clutch some times. Guess it’s time for another new one. Any good suggestions? The standard brand unit crapped out in less then a year…. Haven’t called a dealer to get an oem price but that will be first thing in the morning
 

scotts90ranger

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I haven't looked in a while but I've heard you can get the Motorcraft units online in places. I've seen a few posts mentioning they're about the only way to go, I know it sucks since they're $120ish instead of less than $50...

SMP (standard motor products) is hit and miss with anything, they have several different quality levels and some stuff is fine but others is junk... sometimes hard to tell but at the price point sometimes worth the gamble...
 

OldMan89

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Just called my local ford store and it is a discontinued part from ford. So after market it is!!
 

OldMan89

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Ok so replaced the IAC with a new one. Drove it around and got it to temp and when I got to a long stop light it was immediately apparent that it had no effect on the idle. It idles just over 500. Got it home and sprayed SF around the intake gaskets and the vacc lines. Still nothing…started pulling vacuum lines. Pulled one off the egr and it did nothing at all. No change in rpm’s or anything. Pulled 2 off the vacc block and both of them separately shot the engine to 1200 rpm. Pulled the one off the pressure regulator and it really didn’t have any effect. It stuttered a little bit mabey. So I shut the truck off and heard a hissing noise I hadn’t heard before coming from the brake booster hose grommet. Started the truck back up and pulled that big hose off and the truck idles at a perfect 800rpms….so could that me the problem? I don’t know the inner workings of a brake booster so I don’t know if this is normal or not
 

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My credo
Its probably better to be self deprecating than self defecating.
In this day and age, just because a part is new doesn't necessarily mean it's GOOD.

This is why the parts cannon approach to things is inadvisable.

By searching far and wide you may still be able to find yourself a new Motorcraft valve, which has the guarantee of being good out of the box because ford made sure it was good before it went IN the box.
 

OldMan89

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Still no luck… everything I’ve done seems to make it a little worse or doesn’t change it at all. It starts every single time will shoot too 2500 and fall. Dies the first 2 times then it will stay running at about 1000 rpm for a minute or so then start hunting…goes too 1500 down to 700….goes to 1700 to 500….then 2000 to 500 or below… eventually it will die………. The exhaust smell HORRIBLE. LIKE REALLY BAD. I did new plugs and wires. Tested my coil packs and even swapped the driver side one with a good one I had off or another truck… removed and deep cleaned the throttle body…. Had a ton of build up in the intake but I didn’t remove that due to not having enough time…. Removed the pcv valve (about a year old) and found it gummed up and stuck. Not sure if it was open or closed. Cleaned it and put it back. Removed and cleaned the egr valve. It had what looked to be oil on the inlet side??? Bought some of the STP intake valve cleaner and let it dispense through the TB… it would idle on its own just above 500 after that but if I touched the throttle it would start hunting again…… if anyone has any idea I’m open too them. I’m gunna rent a head gasket test kit today and see if that’s it
 

scotts90ranger

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I'm wondering if there's a capacitor that's mad in the computer or something, or the fuel pressure regulator is on it's way out, maybe pull the vacuum hose off the top of the regulator and see if there's any fuel there, there shouldn't be...
 

OldMan89

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I'm wondering if there's a capacitor that's mad in the computer or something, or the fuel pressure regulator is on it's way out, maybe pull the vacuum hose off the top of the regulator and see if there's any fuel there, there shouldn't be...
There has not been any fuel coming out of it since I’ve been working on it. I’ve checked a few times. Mechanic friend of mine said it could be the map sensor… I never thought of that
 

scotts90ranger

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The MAP sensor does do a lot of everything on speed density, that or the hose leading to it wouldn't be a bad thing to look at...

I'm pretty sure I still have the stock ECM from my '90 around that should interchange with yours (was built in '89), haven't used it in over a decade...
 

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