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Discussion Starter · #1 ·
I've had an issue with my 2004 Mustang GT 5-speed for a while now. Heres a scenario. I'm driving down the road accelerating in third gear, the RPM's get to 3000rpm and I decide to shift to fourth gear. If I hold down the clutch without actually engaging into 4th gear, the rpms drop (like they should) but the needle will fall to zero and the engine dies. Normally I would engage the clutch and down shift or whatever, but the engine should only drop to its set idle right? This problem normally only happens at speeds above 40mph. The car idles fine, and starts fine (most of the time). The car only has 23,000 mile on it and and everything else seems to work fine. But sometimes the engine stall catches me off guard, and since the power steering and pwr brakes shut off, it could be dangerous if I can't pop th eclutch fast enough to get the engine going again.
Do you have any suggestions or anyone had this problem before?:headscratch:
 
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maybe, do you have a "chip" in the car? check the PCV hose going to the plemun for cracks or holes, also try cleaning your IAC wth some carb clean and sea if that helps....
 

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Discussion Starter · #3 ·
I actually cleaned out the IAC yesterday, it looked pretty clean but still cleaned it out anyways. It unfortunately didn't change anything. All the vacuum lines look good as well. As far as the chip goes, there isn't one installed unless the previous owner flashed the computer. I order the SCT X3 two weeks ago and should be at my door step tomorrow (May 2). If there was already an aftermarket tune (which I hope not, since I've been running 87) on the computer, would my new SCT tuner detect it? Or do you think the new program I'm going to install might help the problem?
I thought I read that the IAC is preset for a certain idle and the only way to change it is through the computer, so maybe a new tune would do it. Does this sound right?
 
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well, I for one would NOT install/use the SCT-X3 on your car Untill you get the stalling problem fixxed or isolated....other-wise you could be adding to your problems....
 

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Have you checked.....

Have you checked the mechanical idle stop on the throttle body? It almost sounds like it may be adjusted all the way closed or close to it. Perhaps the previous owner didn't like the idle hang that the IAC causes and reset the mechanical stop in an attempt to drop the idle faster. I recently installed a 70mm throttle body on my 02 and it required some adjustment of the mechanical screw to get it to idle correctly. In my case I found that the air for idling appears to be supplied both by the butterfly and the IAC. Be aware that if you adjust the idle screw you may need to adjust the TPS sensor to have the correct setting at idle.
If the butterfly is incorrectly adjusted maybe the IAC cannot respond properly under the shifting conditions????

Good luck
 

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Discussion Starter · #6 ·
Do you have any other ideas of what might be causing this. The car won't ever stall if say, when I'm slowing down off the interstate and braking, if I let the RPMs drop down while still in gear and then push the clutch once the RPM's are down around 1500, then I can roll all the way to a stop with the clutch pushed in without it stalling. This is the way I normally drive and have gone months without a stall. At first I was thinking that the stall problem was just the way I was driving. In fact, thats what the dealership I bought it from told me, but none of my other manual cars had ever done that so I figured they were full of ****.
 

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I had the same issue on my 04 Mach 1 after installing a tune and a CAI. I replaced every sensor you could imagine with no avail. Then, I turned my MAF 90 degrees towards the outside of the car and problem solved. If you have an aftermarket CAI this may involve either redrilling the holes in the heat sheild or removing the heat sheild all together. Don't waste money like I did. Start/Think small and work your way up.
 

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Discussion Starter · #8 ·
Have you checked the mechanical idle stop on the throttle body? It almost sounds like it may be adjusted all the way closed or close to it. Perhaps the previous owner didn't like the idle hang that the IAC causes and reset the mechanical stop in an attempt to drop the idle faster. I recently installed a 70mm throttle body on my 02 and it required some adjustment of the mechanical screw to get it to idle correctly. In my case I found that the air for idling appears to be supplied both by the butterfly and the IAC. Be aware that if you adjust the idle screw you may need to adjust the TPS sensor to have the correct setting at idle.
If the butterfly is incorrectly adjusted maybe the IAC cannot respond properly under the shifting conditions????

Good luck
The cars RPM's do seem to drop fast if thats what your talking about idle hang. The car idles fine, so would adjusting this mess with that? Do you adjust that screw on the TB and which way would I want to turn it?
 

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Discussion Starter · #9 ·
Also, ClayXmach1, I don't have an actual cold air intake, but have a shaker hood like on your 04 Mach (sweet car by the way). This is the closest I have to colder air. The intake pipe/tubing is stock from the box. My when the Roush Shaker hood was install they changed the MAF position. I thought there was only one way MAF fits in. How do you turn it 90 degrees?
 

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Discussion Starter · #10 ·
Well, I got my SCT-X3 tuner today:myhappydance:. I still have about a 1/4 of 87 in the tank, so I want to run this gas down more, and switch to the 91 before I flash the computer for 91 octane. I did want to try out the tuner so I used its dtc code reader. The only code it found was P1233 which is no signal from the fuel pump. I took the FP fuse out like I read to do, so that P1233 was expected. No other errors though.
I've been doing none stop research on this stalling thing and can't pin point it, except it only seems to happen at speeds above 40mph. I'd just go and replace all the emmisions components if I could but I'm short on cash right now. Do you think the TPS or EGR (Exhaust Gas Recirculation) might be part of the problem?
 

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Hello Dionysus,

Sorry for not responding sooner....too many chores! I am going to try to attach a photo for the 1st time so I hope it makes it. I have drawn a pointer to the adjustment screw and Throttle Position Sensor. Looking at it from the view in the photo you would turn the screw CCW to open the butterfly and raise the idle air through the throttle body. When I installed the Ford Racing 70mm throttle body on my car I found that the IAC is supplying part of the air at idle and the throttle body the remainder. If I disconnected the IAC the idle would drop and vice-versa. What I also found was if I adjusted the screw on the throttle body the idle would remain the same through a range. If I increased the idle at the throttle body the IAC would close down to maintain the idle RPM specified in the computer and conversly if I closed it down the IAC would respond and supply more air. As mentioned this only happened over a limited range of adjustment. If I opened the throttle body too much the IAC could only close down so far and the idle would rise at some point. At the other end it if I closed the throttle body down too much the IAC had problems supply enough idle air. What I propose may help in your situation is to adjust the screw so that the throttle body is supplying a larger percentage of the idle air. Maybe under your circumstances the IAC
is closing down after you shift and the throttle body isn't open enough to keep the idle up. This is offered as a guess only, I have not experienced your particular problem, obviously a fortunate thing!


If you choose to pursue this avenue the first thing I would suggest is too look at the screw and see if there are any signs that it has been moved. When I adjusted mine I had to use some pliers to turn it as the threads fit snugly so it can't move and lose adjustment. I would also be wise to check the TPS voltage setting at idle to see where it is set (key on but engine not running). On my car (02 GT) this was done between the Gray/Red and Gray/White wires. The instructions I got from Ford said this voltage should be between .96-.98 volts although my Haynes manual allows the setting to be 0.50-1.0 volts. If this is off then it could mean that the throttle body adjustment screw may have been moved because the TPS voltage will change with an adjustment there. Or possibly it could indicate a failing TPS. I would also make a mark on the screw and the throttle body so if all else fails you can return the screw to the original setting. At this point you could try adjusting the screw so that the throttle body is supply more idle air. If your car reacts as mine did you should be able to adjust it open slightly more and maintain the same idle RPM. Just remember that if you choose to keep the throttle body screw adjusted at a new setting it will change the TPS idle voltage setting and it will need to be checked. The TPS setting can be adjusted by loosening the two mounting screws and rotating the TPS. It's a little tricky because a small adjustment goes a long way and it tends to move when tightening down the screws. Enough patience and swearing will get it done. If you run out of adjustment in the holes the info I got from Ford says you can drill the holes out slightly for more adjustment. If you adjust the TPS setting you then are supposed to disconnect the battery for 15-20 minutes. When you reconnect apparently the computer "relearns" the TPS setting.
I hope this was not too long winded and helps. I am a home mechanic only and if any Pros out there see a problem with these suggestions please comment!
 

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Discussion Starter · #12 ·
First off, thank you for the great info and the time you have taken with looking into my problem! I looked at the adjusting screw and it doesn't appear anyone tampered with it. It is threaded out quite a ways too. Right now, I'm going to test the TPS and see where that is at. I'll let you know what I find out. Also, I read in my Chilton manual that the EGR can cause idle issues too, depending on the flow through it. Any takes on this?

Thanks again:thumbsup:
 

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Discussion Starter · #13 ·
Alright, I tested the TPS. I didn't have an assistant with so I just turned the throttle on the TB myself. When I turned the key on, the TPS read 1.00 volts. At full throttle, it read 4.62 volts.
 

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Stalling

I've never heard of pulling out the fuel pump fuse and I would definately replace it and see what happens. If its telling the ECU that there is no signal from the FP its possible that the ECU is pulling a lot of timing out of it to compensate for "no fuel", good luck.
 

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Discussion Starter · #15 ·
When reflashing your computer, it's recommended that you pull your fule pump fuse, and/or any other acc. the might turn on and draw power when uploading/downloading the new tune. Since I was just checking for dtc code, I probably didn't need to pull the fuel pump fuse, but did it anyways. After putting the FP fuse back in, the dtc checked no errors.
 

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Discussion Starter · #16 ·
So if I try adjusting the throttle body adjustment screw, would it be best to have the car running to see how it reacts to the change, instead of adjusting and finding out after I turn the key for the first time?
 

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I had mine running when I made my adjustment, a shot in the dark otherwise. I see you checked your TPS voltages and they look like they are in spec. I also see you installed a SCT tune, did you check to see what idle RPM it is loading? My Diablosport has a place where you can adjust the idle RPM. It might be good to check on this and see if the car is holding the programmed idle RPM for starters. If they are in sync then try adjusting the screw up a little. Do it when the engine is warmed up but the radiator fan is off....don't need another variable in the mix!
 

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Discussion Starter · #18 ·
The Tune I loaded was a custom tune from the dealer. I see you can data log with these tuners. Do you think I might find a clue to this problem if I data log and let the car do its stall thing? Ive been thinking about just replacing the IAC but cleaning it didn't help so I don't want to waste the money, if the problem is something else.

Also, last night, the car stalled only the RPM's weren't high. I was driving a 55 and shifted into 5th gear. Normally I drive in 4th at this speed cause the RPM's sit to low in 5th. But I did have it in 5th,
RPM's at about 1200, at 55mph, I pushed the clutch in approaching a stop light and it died. I just just threw it in 4th and popped the clutch and she ran again, but it did die during a different scenerio. It seems like it won't idle if the gear is set to low for the speed when the clutch is pushed in too. But no matter what gear your in, as long as the clutch is pushed in, it should idle, right?
 

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dionysus, I feel your pain. The stalling has happened to me a couple times as well. I have a 2004 Mustang GT with a BBK 75mm throttle body, C&L upper intake plenum, C&L intake system. I also run a K&N air filter. The stalling is rare, but it's a pain in the a$$ simply because no power steering and power brakes make life interesting for a couple seconds. I would recommend cleaning the throttle body, the MAF sensor, and the IAC. They're all easy to clean and the MAF sensor has a bad habit of stalling this engine when it gets oily from excess oil on the air filter. The MAF sensor can be cleaned by spraying some TB cleaner into the sensor's hole, and spinning a Q-tip softly over the wire. Be careful, the wire breaks easily. To clean the IAC, spray TB cleaner into both holes and use a Q-tip to clean the mechanism inside. If your problem is the MAF sensor, run paper filters instead of K&N. That will keep EVERYTHING much cleaner in the intake system, and you don't have enough mods to really need more than a high quality air filter anyway. Worst case scenario, buy a paper filter and do test runs before installing it and after. I can bet you won't notice a difference.

Hope this helps.
 
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