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1994-1995 5.0 Mustang SN95 Tech Forum

5.0L Talk | 5.0L Tech | 94-95 Tech | 1979-1993   1994   1995   Upload Pictures | Timeslips | Power Adders | Mustang Tech 


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Unread 12-06-2009   #1 (permalink)
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Default 1994 Mustang gt iac problems

ok i give up i have no ideas anymore... ive got a 94 mustang gt with trick flow upper and lower trickflow elbow and bbk 70mm throttle body.. My problem is that my idle is all messed up.. when im driving and i shift the rpms jump up about 500 then it takes forever for them to drop when i come to a stop.. also when i let off the gas its like cruise is on.. So i did all the re setting of the idle and tps and iac.. I even put a know good iac on and it still acts the same but when i disconnect it then the idle is fine and the rpms drop bettween shifts... Some people tell me i have a vacum leak... But i just want it to run right.. Any help would be great.. I also have e cam and exht. and a cai thats about it.. thanks for any help

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Unread 12-06-2009   #2 (permalink)
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I don't have an answer...just the same problem on my 95. I have mostly the same parts except a cobra intake instead of TF. I even have it tuned to drop as fast as possible, yet it still does it.
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Unread 12-06-2009   #3 (permalink)
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All this sounds very familiar. I ended up just replacing my iac and tps and cleaned my mass air. WARNING, while in the process of trying to find out what was wrong I was sold the wrong iac or tps, one of them, can't remember. It caused my car to idle very high and my headers started to glow. I disconnected the new piece and took it back. It looked identical to mine and all but it wasn't for my car. A nice guy there helped me in trying to find out why this part didn't work even though it was the part listed for my 95. Turned out to be for a Mazda or something. I ended up going directly to Ford and got the rite piece because all was good afterwards.
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Unread 12-06-2009   #4 (permalink)
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I can see that happening with the wrong iac. That is a little different than what is happening with mine atleast, probably mylittleponie's too.

I have a new tps and I've cleaned my iac and everything. Just like mylittleponie said...when I shift, the rpm will jump up 500 or more; and there is pretty much no engine braking (seems like cruise is on up to 2000 rpm). When I stop (or push the clutch in for a while), the idle takes forever to come down all the way. Mine will hang at 2000 for a few seconds, then drop like a rock to 1300 then it takes 1-2 minutes, at least, for it to drop to normal idle (~800).
Also...when moving and in neutral, mine will surge between 1300-2000.
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Unread 12-06-2009   #5 (permalink)
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Quote:
Originally Posted by mylittleponie View Post
ok i give up i have no ideas anymore... ive got a 94 mustang gt with trick flow upper and lower trickflow elbow and bbk 70mm throttle body.. My problem is that my idle is all messed up.. when im driving and i shift the rpms jump up about 500 then it takes forever for them to drop when i come to a stop.. also when i let off the gas its like cruise is on.. So i did all the re setting of the idle and tps and iac.. I even put a know good iac on and it still acts the same but when i disconnect it then the idle is fine and the rpms drop bettween shifts... Some people tell me i have a vacum leak... But i just want it to run right.. Any help would be great.. I also have e cam and exht. and a cai thats about it.. thanks for any help

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Curious, do you have any trouble codes listed? Mine is showing that the tps is out of self test range, the pcm read only memory failed, and the right and left bank o2 sensors are showing a lean condition. Those show during the engine off test.
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Unread 12-06-2009   #6 (permalink)
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well yes my check engine light is on had it read and it had a coolant sensor bad plus my bank one o2 sensor was bad... and showed my idle out of range..now i put all the new stuff on and kept the same iac and tps... now mine doesnt surge but now its funny it still takes a min for the idle to drop in between shifts but idles fine now.. the only thing i did was adjust the idle air screw to where its one turn closed.. going to my buddys shop to read my codes and see why they came back on... i just hate how it stays reved so hi.. someone said this is a common problem on the 94 and 95 stangs.. so you got me lol
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Unread 12-06-2009   #7 (permalink)
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oh and mine was running rich not lean
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Unread 12-06-2009   #8 (permalink)
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Weird...SOMETHING must be causing it...they didn't do that from the factory.
Mine is going in where I had it tuned to get a wideband checkup to help find out what is really going on soon. we'll see what that turns up.
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Unread 12-07-2009   #9 (permalink)
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You need to replace the O2 sensors. Those are most likely NOT the cause of your idle problems, but they still need to be replaced.

About your idle issue:
You are using the NEW IAC and it still doesn't idle correctly?

The TPS needs to be set at a certain voltage or it won't run right either. The TPS stands for Throttle Position Sensor. It senses how much your throttle plate is open or closed and adjusts the air/fuel accordingly. So if it's not set correctly it can cause problems.

Mustang Basic Maintenance and Technical Articles
Check out the "solve idle problem" section on that link I gave you.
Do those things to your car and set your timing also. See if any of those things fix/help your issue and let us know from there.


One last thing: When was the last time you gave your car a complete tune up?
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Unread 12-07-2009   #10 (permalink)
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Default idle problems

I also have a 95 gts. all of it is trick flow. heads came intake .Mine does the same thing.I've done everything that you guys are trying. Then I ran across an old fast ford issue. In this article they were having thew same issues. what they did was change to the 93 lx computer a9L ect. because it has more tune ability than ours have. I also have the 24lb injectors, bbk long tubes with flowmaster dumps, hurst shifter,h&r springs,I put mach one struts on the front, monroe gasmatics on the rear. I run mine at roadamerica so I still have the 273 rear in it.it gets fantastic gas miledge 34.801 miles to the gallon. as long as i stay out of it around town i get 22 mpg.she runs 12.59@104 in the quarter mile.But it still has the same driveabilty problems. I don't think that I can get it to run any better than it does now.Ones I get the computer changed over I'll let you know how it works.I hope that it is the fix we all need. I'll keep you posted.
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Unread 12-07-2009   #11 (permalink)
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Well...the o2 sensors will probably be replaced sometime soon.

As for the iac valve...no it is not new, I am currently working on getting another.

The tps adjustment article is interesting. I just replaced mine, and the voltage was off just a little bit...though I don't remember being able to adjust it.

plugs, filter, tps, wires, distributor, coil are fairly new on mine. I haven't messed with the base timing yet.

It is parked for now as I neglected to put the hood pins back in one day last week before I drove it. :sigh: Had the hood come up. Luckily the hood was the only thing damaged. Anyway...it has some stuff waiting to happen.
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Unread 12-07-2009   #12 (permalink)
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Quote:
Originally Posted by good'ole302 View Post
I don't have an answer...just the same problem on my 95. I have mostly the same parts except a cobra intake instead of TF. I even have it tuned to drop as fast as possible, yet it still does it.
I have the same f&^%$ problem and almost the same modifycations too, Mine is a 94 GT and it has, Edelbrock heads, cobra lower and upper intake, BBk 65mm TB, racing MAF, custom CAI, K&N filter, racing cams (do not know spec), shorty headers, H pipe, flowmaster mufllers, etc. I recently changes my TPS and O2 sensors, and the same **** happens.

My mechanic told me that is a combiantion of the TB not clousing completely and a bad IAC, but I change the IAC and problem remains, so i am not changing parts like crazy until i confirm what it is, i am trying to get another TB and IAC valve from a friend in a loan to veriry if that is the problem, but have not the parts yet.

lets solve this between all, please keep posting and lets keep everybody updated with everysbody evaluation and tests.....
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Unread 12-08-2009   #13 (permalink)
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Hmm. Good idea on trying another TB. I still have my factory one up on a shelf...and am working on getting another iac. I'll have to wait till my school finals are done though. My shop is full with 2 other vehicles, and I have a ton of studying to do. I'm guessing we'll get it figured out one way or another...
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Unread 12-09-2009   #14 (permalink)
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Quote:
Originally Posted by good'ole302 View Post
Well...the o2 sensors will probably be replaced sometime soon.

As for the iac valve...no it is not new, I am currently working on getting another.

The tps adjustment article is interesting. I just replaced mine, and the voltage was off just a little bit...though I don't remember being able to adjust it.

plugs, filter, tps, wires, distributor, coil are fairly new on mine. I haven't messed with the base timing yet.

It is parked for now as I neglected to put the hood pins back in one day last week before I drove it. :sigh: Had the hood come up. Luckily the hood was the only thing damaged. Anyway...it has some stuff waiting to happen.
How far off was the voltage on the TPS? Even a tenth of a volt can make a noticeable difference. And to adjust the TPS, you have to loosen the bolts just enough to be able to move it. You just turn the TPS in a clockwise/counter-clockwise motion to adjust the voltage. I got mine to read .96 and it's supposed to be at .97-.98.

The TPS would be where I would try first.
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Unread 12-10-2009   #15 (permalink)
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Default idle

the problem your talking about isnt your iac or tps etc..its the vss wire picking up that the car is rolling and will make the car run at either a high idle status or a really low idle status..when you let off gas and press clutch the engine you think would drop to say 7 to 800 rpm but it wont mine stays at 1300 till i come to complete stop..its the vehicle speed sense wire telling computer car is still in motion..all 94 95's have this issue and its not fixable unless you unlpug the vss from car..if it started recently then you might have a bad o2 and and bad vac leak..everyone so far that has responded to this i had all you guys issues..i had vac leak, bad egr, bad 02's, bad ign mod, bad fuel press reg, bad tps and the car ran like a total nightmare would barely run at all..i replaced everyt freaking sensor on the car including the ect and iat and ir runs awesome now...fyi..after mods on 94 95s its best to do a dyno tune..trust me when i say this its well worth it and those on here who say you dont need it need to get a clue..im one of 4 guys in my click that have a sn95 and let me tell you all of us when and did a tune..a combined 4 car hp increase of 195 hp between the 4 of us...trust me do it and you will love it..
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