Surging idle help me fix once and for all!

99FiveOh

10 Year Member
May 20, 2006
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J-Ville, FL
Of course I searched for answers on this and all I turn up with are threads full of people suggesting replacing every part under the hood! Definitely not a solution at all.

So these cars seem to be plagued with this problem. Some people have zero issues and others have nothing but. My last 94 never had this issue, it would idle all day long rock solid. My current car hunts for idle a few seconds then dies if I don't keep it running. It only does is when it's been running for a bit and I come to a complete stop. Drive throughs are a nightmare! It's embarrassing having to restart.. makes people think I'm driving a clunker or something! So far I've tried to replace the MAF and IAC to remedy the problem and still the same result.

I noticed it got worse when I took some timing out. I'm not exactly sure where the timing is because I believe my balancer has slipped a little. But I pulled timing until it stopped pinging on 89 octane so I'm probably right on 10* or so. The light shows it's around 5*

So guys, who has actually figured out what is wrong and fixed the problem? Since a good number of these cars suffer from hunting idle/stalling I'm sure there MUST be a common issue. I've been driving these cars for years and converting to Fox TB always fixed it for me.. however that's not an option at the present. Thanks for your input guys. BTW, motor is stock.
 
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99FiveOh

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May 20, 2006
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It's one of those plug and play chips they used to sell. I'm not sure what it could be doing and I'm afraid to pull it off the computer. Haven't done an idle reset so I'll try it. I just know that even if it does fix it, it will probably be temporary as the computer will eventually relearn itself into oblivion!

Any success with drilling a small hole into the tbody blade? Bandaid or not, if it fixes it that's all I'm after.
 

RIO5.0

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Feb 16, 2001
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I had a link to an idle reset... I used it in the past with good results. Cant find the damn link but its in the forum....:mad:

Myself I never had idle issues with either stock or my Fox swap. Have heard of the "hole" but never had to use it. If the state of tune is ggod and you have no stored codes than maybe the reset will help.

If you replaced all those parts and never did this full reset than it may help your problem...I'll keep looking for it to post up.
 

99FiveOh

10 Year Member
May 20, 2006
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It's one of those performance boost chips. It's not a SCT type chip that had a tune loaded into it. It has a bunch of dip switches on it that are set a certain way. The car came with it in there and the guy I bought the car from said he never even knew it was there the 6 years he owned the car.
 

toyman

SN Certified Technician
Jul 19, 2007
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And why do you believe the chip is not the cause of the problem? Pull it, you may be pleasantly surprised. And if you believe the HB has slipped even a little bit you are courting trouble. It's not a timing issue but rather an imbalance issue. The consequences can be serious.
 

BlackVert

15 Year Member
Oct 3, 2003
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And why do you believe the chip is not the cause of the problem? Pull it, you may be pleasantly surprised. And if you believe the HB has slipped even a little bit you are courting trouble. It's not a timing issue but rather an imbalance issue. The consequences can be serious.
i agree completely with both of these points.
 

99FiveOh

10 Year Member
May 20, 2006
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J-Ville, FL
I know the chip is not the problem because before this car was finished being put back together, I threw the computer into my other 94 GT and drove it for about a month. I wanted to see if the chip made a power difference. My other Mustang idled fine with this computer in there. I believe this was one of those chips that sent the "hot" settings to the spark plugs and injectors for a little more power. They used to advertise them on those Sunday TV shows like Horsepower and Shadetree Mech.

Anyway, I reset the computer today and it did fine most of the day. But on the way home while stuck in traffic it started hunting again. I am smelling raw fuel coming from my passenger side fender where the charcoal canister is. Does this mean I need a new canister or new lines? This could be the cause if it's a vacuum leak I'm thinking. Whenever it starts hunting I can pulse the brake pedal and the idle will settle down for a bit. I guess next I'll be solving the fuel smell problem as it stinks bad and can't be good!
 

final5-0

Mustang Master
Apr 6, 2003
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Mark

It would seem ... as you've said ... that pcm/chip in a different car would
give you proof that an unstable idle is not due to the pcm or chip :scratch:

however ..............

That pcm & chip ... The're just PART of the WHOLE system :Word:

The pcm makes decisions based upon what the various sensors feed
to it ... don't ya see :)

You could have O2's, meter, tps, and more :crazy:

That are enough different between the two cars to make for an
unstable idle ;)

The sensors and idle driving condition are both VERY involved in the
Closed Loop part of the tune

In Closed Loop ... the sensors are running the show ... as they say :D

Now ... You've already given us info that gives us a clue :banana:

Good manners for a while after the pcm reset :nice:
but
Over time ... the ugly drivablility deamon returns :notnice:

That tells us the pcm (adaptive strategy) is making changes to the point
of causing the issues

It is making those changes to compensate for something (sensors or even hot rod
parts can cause it) that is not right :bang:

Like has been said ... I'd pull the chip and do a pcm reset

Grady
 

Chythar

15 Year Member
Aug 26, 2004
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A gas smell in that area points to a cracked vacuum hose, they vulcanize over time with all the heat cycles. Just get some cheap hose at your local parts store. If you have another car you can use, I'd tear the car down first, so you can see what's there and know how much hose you need. There are a couple of 90* hoses that may be hard to find and replace.

All you need to do is take the passenger wheel and fender liner off; everything is easily accessible then.
 

99FiveOh

10 Year Member
May 20, 2006
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J-Ville, FL

You are correct, however, if there is a sensor or part that is causing the issue how is taking the chip out going to fix it? These cars with all brand new parts have this issue too. I've owned them before, replacing every single part under the hood, seafoam, timing, etc... to no avail. The only thing I've ever seen fix it was swapping to a fox throttle body, but that's not an option for me right now.

What I'm stumped on is these cars didn't do this when they were new, so something has to be causing it.

I will humor you and pull the chip tomorrow. Who knows what will happen. But I just can't see it doing anything but messing with timing and spark curves slightly. It probably doesn't do anything at idle I'm thinking. And if it can run a different completely stock car flawlessly then there's something amiss here.

Now, the EGR is bypassed/plugged...meaning the valve itself is still there, but no tube coming off the header. I've ran a few other SN95's this way without issues including my last one so I can't see it being a problem. I do get a CE light periodically but the Snap on scanner at my brother's shop can't find anything besides my smog equipment missing which is a soft code.