Possible Vacuum Leak/Idle Problems When Warm - Ford Mustang Forum
 
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post #1 of 7 (permalink) Old 11-10-2013 Thread Starter
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Any Suggestions? Possible Vacuum Leak/Idle Problems When Warm

Figured I would post this up in the tech section out from my big long thread on my car. Here is the basic info on the car.

1998 Mustang GT Motor swap teksid block MHS stage 3 PI heads and stage 3 N/A cams.

New PI intake I purchased back in 2011 that never got installed just sat in the box in a closet.

PP fuel rail kit w/adjustable FPR.

New 39lb injectors, and new 90mm lightning MAF.

78mm BBK throttle body/plenum.

Pypes LT headers w/pypes shorty o/r h pipe.

Tuner sent me a XCAL3 with start up tune.

Now here below is the basic information on what problems I am having.

Well I took the car this past Tuesday to get it tuned. My tuner found a vacuum leak at my intake on the driver side which is bank 2. So I had to take the car back home to pull the intake, inspect everything, and install with new gaskets. Get everything together hook battery back up and start the car. It sounds much better idles better then it gets to operating temps and just starts running like crap. When you gave it throttle it would idle back down and die unless you gave it throttle then it would hang up and drop back down and die. So I called my tuner and was talking to him. He told me to plug in the XCAL3 and watch my long term fuel trims. They was sitting right at 1.25 and the the short terms was moving around in the high .70's- high .90's. He told me that with the LTFT's reading 1.25 I was getting a vacuum leak somewhere. Now here is the funny thing. I decided to pull the car out of the garage and see how it drove around the street. While still monitoring the LTFT on bank 1 was in the like high .80's- 90's area then I got a CEL for bank 1 running rich. Yet bank 2 the driver side never changed. It didn't stay like that for long it ended up going back to 1.25 on both LTFT's. So I pulled the intake off and put RTV on the gaskets on both sides. Got it all back together and LTFT's was good right at 1.00 until I pulled it out of the garage and drove it down the street. I pulled up to a stop sign and the idle dropped down the died. When I restarted the car and the monitoring the LTFT's had jumped up a little bit. Are these fuel trims something to legitimately go off from or am I doing this all wrong and my problems are coming from something else? I am completely at a dead end here and just about getting frustrated with this damn motor. I have literally spent just about all of my time home from my deployment messing with this thing and I'm getting sick of it because I just want it to be done and tuned so that I can spend more time with my family and get started on other projects. Does anyone have an idea on any of this?

You can go out when the car is cold start it up and it runs fine even getting 1.25 on the LTFT's. You can rev the motor a little and it idles back down and holds rpm's as it should. Once the car gets warmed up it all goes to hell and the idle gets a little rough. When you give it throttle it will idle back down and get low and 90% of the time die. It never seems to be able to catch itself and idle on its own after raising the rpm's. Once the car dies 90% of the time you have to apply the throttle to get it to start back up. Then the rpm's raise up and it will not idle on its own.

I figured out the reason I was seeing the 1.00 LTFT's after doing the gaskets was removing the battery cable and computer going through the fuel trim deal. I'm no expert on this computer fuel injection stuff so figured I would try here for some help before I take the car back to my tuner and let him figure out what is wrong. My conclusions are a few possibilities.

Intake still is getting a vacuum leak and considering everything I have tried possible that I just got a faulty intake.

o2 sensors are reading crazy and causing the problems.

Possible bad IAC valve.

Any help would be appreciated!


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post #2 of 7 (permalink) Old 11-10-2013
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Dying when letting off the gas screams iac (idle air control valve) I'm not saying that's what it is. I would just check that over.


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post #3 of 7 (permalink) Old 11-10-2013 Thread Starter
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No way it could be. I got to messing around and pulled the vacuum hose off the egr and it wasn't pulling hardly any vacuum. So I pulled the vacuum line off the egr vacuum solenoid and popped it on the egr. Bam it idles now but when you drive it has a hesitation to it because the egr valve is staying stuck open. None of this makes sense. I'm about to pull my dang hair out.

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post #4 of 7 (permalink) Old 11-14-2013 Thread Starter
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Screw got turned somehow on the throttle body. Didn't know it would cause so much problems.

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post #5 of 7 (permalink) Old 11-14-2013
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Glad to hear you got it figured out.
I didn't know those screws could cause that much of an issue either! Lol


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post #6 of 7 (permalink) Old 11-15-2013
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I'm glad you got it figured out. I was thinking that the reason it would still run and idle on cold start was because the computer is in open loop. I'm not too sure if, in open loop, the EGR system is disabled and when it gets to operating temperatue it then enables it and sicne the vaccuum hoses were swapped (at least thats what it sounds like from your posts) it was causing it to die. Again, that's what I was thinking after your OP (I may be completely off) but it doesnt' matter since its up and running

Either way, enjoy it, enjoy you time home with your family, most importantly. Thanks for your service!

Matthew 26:52-54 / Go Pack Go!

1987 Mustang GT Hatchback - 2V Mod Swap In The Works

1997 Lincoln Town Car, PI Intake/Cams, Sofa-On-Wheels, "Fat Tony" we call it

2001 GT Convertible - D1SC / Geared / Cammed / 440wh 400wt - TOTALED 2/2019
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post #7 of 7 (permalink) Old 11-15-2013 Thread Starter
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EGR is not opened at idle nor wot. Its deleted from the tune now so all egr junk is getting removed. Much cleaner look in my opinion. I think the exhaust gas flowing in at idle was helping with the throttle body adjustment off. Yet it made it show as a vacuum leak of course as it was.

Thanks man I appreciate it.

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