Roush 95 s351 eratic idle and shutting off

Your problem probably isn't s351 related, it's a generic problem that 5.0 owners have been battling for years.

I've had the surging problem over the years, and here's what they were: Header exhaust leak, Bad or dirty IAC, TPS screwed up and bad vacumm lines.

Also here's a checklist one of the member here did up.

http://forums.stangnet.com/showthread.php?t=534062

Assuming all is well...

HERS351 said:

hey guys i need help i bought my wife a 95 s351 na but it runs like crap she refuses to drive it cause it is not fun.it is all stock with 18,000 miles it is beautiful but it will not idle right it surges up and down alot or almost stops when you pull up to a light or it just shuts off all together.i thought i saw someone talking about the same problem and someone suggested some electronic gizzmo to fake out the computer i was wondering if anybody has any success with it. i know it is a common problem in these models with the pro m so i am sure some one has found a cure for this. please help wife right now wont drive it only washes it and puts int back in the garage but she really does want to drive it. thank you in advance!!!
LANCE

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Assuming that all the factors in the response above are working correctly, yhen I would invest in an "air adjuster", made by Interactive Systems. 770-720-1259. It works like a charm. Took the surge in our 95 from annoying to virtually non existent. Good luck.

Dan

The idler air adjust plate is a bandaid for a real problem, yes sometimes it works, but it's still doesn't truely fix the problem.

I have a '95 R-code S351 that had the same problem and it too made the car annoying to drive. Start with the basics and go from there before you start replacing/adding components. First, you want to understand the reason that the idle hunts. The reason for that is usually because the exhaust readings (O2 sensors) does not correspond with the air inlet readings of the mass air sensor and the exhaust readings will either be too rich or too lean. The engine's computer will "hunt" up and down it's idle setting parameters to try and match the mass air flow sensor's air intake readings to the O2 sensor exhaust readings, hence the "hunting" idle. Unmetered air (vacuum leaks) and/or incorrect mass air flow sensor signals are common problems. The "air adjuster" mentioned by Footnfan will tweak the mass air flow sensor's signal and can compensate for an incorrectly functioning or calibrated mass air sensor. However, if your mass air flow sensor is functioning properly, then it won't help you.
First, check for vacuum leaks. Any vacuum leak downstream of the mass air flow sensor will create a hunting idle. I've been able to correct numerous hunting idles by finding cracked rubber hoses and torn intake boots.
Second, try removing and carefully cleaning the mass air sensor's sensor element. Dirt build-up on the sensor element will create incorrect sensor readings. This is especially true if you have an oiled filter element (such as a K&N filter). Sometimes the oil used on the filter will contaminate the mass air flow sensor element (especially a filter that has had too much oil applied to it) and create false readings.
On my particular S351 I found a cracked vacuum hose and a broken PCV valve. I also replaced the idle air control (IAC) solenoid with one for a 351 Lightning pick-up. I also installed the Air Adjuster because the mass air flow sensor had been replaced with a 90mm Pro-M and I thought that maybe the sensor may not have been calibrated properly. After the above changes and performing the usual TPS sensor adjustment and computer memory clearing, my car idles and drives much better now and the "fun factor" has been restored. Anyway, hope this helps somewhat.

HERS351 said:

thanks for the replies. has anybody ever had a chip burned to solve these problems? i spoke to a mustang shop by me and the owner said he recomends puting it on a dyno and to burn a chip. i am not sure if that will fix my problem or would just be a waist of money/
thank you for the help

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I was one weekend from doing the same thing, but the air adjuster solved it. Even with a chip, your mass air system will have a hard time coping with running smoothly at idle and wider open. Others will have a ore learned description, but I am convinced that a chip MAY not be in your best interest.

My mechanic drives a mongo 03 Cobra. He had burned several chips for mass air blown cars. Post installation of the air adjuster, he no longer advises you burn a chip for idle roughness....yes for other symptoms, bit not for this issue...assuming the rest of the intake system and other systems are in good working order.

Dan

If it ran good after you disconnected the battery, that's probably because the ECU was heavily compensating for the problems the car had/has and it needed to be "re-learned" after the changes you made. Hopefully, whatever you did cleared the problem. Keep us posted.

If you are on the stock tune a dynotuner that has eec4 experience can tune that outa there. Most of the time it is not mechanical. Like I said, most.
Very typical with the 94-95's. My 95 S351 idled like a Lexus after my first dyno tune. The only part of the tune on the 94-95's that is almost impossible to completely get rid of is the light throttle stumble.

Lance,

Have them burn a chip. It's that simple. Steve at Powertrain Dynamics in Huntington BEach CA is a SCT tuner. DId my cars. May be able to mail you a chip. It will not hurt the value of the car at all.

No overspray in that area. Saleen does not spray parts when they are on the car unless something happened before it left the factory.

also for other s351 owners do you have any paint overspray in the fuel door area? i have two 95 s351s and both have it. i assume it is from saleen blending the paint with the ground effects. just currious?
thank you again
LANCE[/QUOTE]


If your car was equipped with 10in rear wheels they could have cracked the paint on the rear fender lips when rolling them (and had to respray the quarter panels). I have seen this on a few cars.