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Old 04-19-2006, 01:12 PM   #1
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Question My car seems to idle rellay rough, and miss badly

Hi everyone. Am new here. any ways, I have this problem with my car. As you might know, is a 94 mustang GT. And recently it has started to run rough, and idle very badly, and thus seems to be getting worse.
So far, what I've done to remedy it, was change the wires, check the plugs gaps, also swapped coil, and changed the stator. Did a cap and rotor swap. Upped the fuel pressure, changed the timing to many different settings, all with the same result. I am beginning to believe that either I got bad fuel, or my timing chain has stretched. Any suggestions, or guesses of what I might be missing? I don't believe its the fuel filter, as throttle response is good, specially after 2000rpm, and it starts great. Normal for a distributor car. Not like how them old chevys would crank on forever. Enough picking I guess, but here are the mods I've done to my ride.
Upgrades/pony power adders, etc, etc... Cobra computer, bored 30 over block,Speed Pro Forged flat top pistons, Trick Flow aluminum heads, Holley systemax 2 intake, 30 lb injectors, FRPP E303 cam, 1.7 roller rockers, 80mm PMAS(Pro M) MAF, 75mm Throttle body, Fluidyne Rad., underdrive pullies, Tremec TKO 600 tranny, alum flywheel, Centerforce Dual Friction Clutch, alum driveshaft, upper and lower rear control arms, 3.73 gears, Auburn diff., 31 spline axles, cover support, 255 lph fuel pump, fuel press. reg., long tube racing headers, MAC Prochamber, and Cat back exhaust. Cobra front brake conversion, Cobra R rims(eagle brand).
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Old 04-19-2006, 01:16 PM   #2
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Re: My car seems to idle rellay rough, and miss badly

you could try to clean your MAF sensor, cheap and easy. It may do nothing but you never know. Use ON contact NO residure cleaner for electrical parts.
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Old 04-19-2006, 01:22 PM   #3
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Re: My car seems to idle rellay rough, and miss badly

Oh yeah, I had forgot to mention them as well, I did clean the mass air meter and did the tps swap. I had recently pulled a throttle enhancer off the car. There is where it was really noticeable. I'm beginning to believe that its my mass air meter as well. As I had put on a Pro-M(PMAS). I have a feeling that they didn't program it right, as they had called me and asked why I wanted it recalibrated. I told them yes, since I have a cobra computer on the car. He told me that there was only 4% difference on the setup, and shouldn't hurt it. But the car ran fine when it was installed. I had also noticed that when I was cruising down the freeway that it would feel like something changed, like it almost died, or had no power. This was even before doing all that I done recently, including taking off that tps enhancer. So, my guess is that it is the chain. Whi knows. Thanks for the tips, everyone
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Old 04-19-2006, 03:26 PM   #4
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Re: My car seems to idle rellay rough, and miss badly

Maybe you should have it tuned somewhere else?

Have you done a compression check?
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Old 04-19-2006, 03:48 PM   #5
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Re: My car seems to idle rellay rough, and miss badly

Hi Brent, I try to do all my own work. Last time I had someone do anything on any of my vehicles, was a major dissappointment. A whole other story with that. But anyways, the tune up is fine. Also, I had done a compression test. All cylinders were about the same. So, thats why i'm leaning towards timing chain, or gas. We'll see when I get my set, next week. Thanks.
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Old 04-19-2006, 05:39 PM   #6
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Re: My car seems to idle rellay rough, and miss badly

Well good luck with it. Timing chain could be it... but if it is you better change it fast before it gets worse and tears something up.
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Old 04-19-2006, 06:52 PM   #7
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Re: My car seems to idle rellay rough, and miss badly

Yes Brent, I do agree with you there. I haven't driven it much since it has been getting worse. Thank goodness for spare vehicles
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Old 04-23-2006, 07:14 AM   #8
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Re: My car seems to idle rellay rough, and miss badly

if your timing chain has stretched to that point, you would hardly be able to drive it.. however.. my '89 jumped the timing gear, it actually jumped off one set of the double teeth, car barely ran.. I was able to make it home though
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Old 04-30-2006, 11:37 PM   #9
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Thumbs down Re: My car seems to idle rellay rough, and miss badly

Well, to my dissappointment, I had changed the timing chain on my car. And it still does the same thing. A fellow coworker I used to work with told me of a similar situation about his older mustang, with similar problems too. He stated he had done everything like I have done. But then he swapped out the computer in his, and it fixed the problem. So low and behold, I'm going to be doing that next too. By the way, the timing gears sound awesome Makes it sound like I'm running a supercharger under the hood. Maybe after the computer swap, I can scare away some ricers that keep wanting to run me. We'll see.
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Old 05-25-2006, 07:09 PM   #10
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Re: My car seems to idle rellay rough, and miss badly

Hello again all, its been awhile, and still no luck on this beast of a car. I had finally did the computer on it, but of course, still runs the same. I'm now in the process of getting another MAF. Since its about the only thing I haven't touched yet. Figures. Oh well, if not, anybody want a few bolt on parts if I decide to strip this POS? We'll see. Thanks everyone.
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Old 05-25-2006, 11:10 PM   #11
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Re: My car seems to idle rellay rough, and miss badly

Idle Air Controller. I had the same problem with my car. Unbolted the IAC(be careful with the gasket its fragile if its old!) and goto advanced or whatever and get some throttle body cleaner... Spray the **** outta the IAC inside and kinda shake it and let it spill out. Then spray the two holes in the throttle body that the IAC connects to. Bolt it back up(make sure the gasket is on) and hope for the best. Also.. if the gasket is in ****ty condition right when you take off the IAC, that could be your problem. Any little amount of extra air that gets in to the sensors of the IAC will **** up your idle to no end. Best of luck.
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Old 05-26-2006, 01:54 PM   #12
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Smile Re: My car seems to idle rellay rough, and miss badly

Hi, and thanks for another tip. Its not the IAC(idle air controller) It is working fine, and I have to take that off to get to the TPS anyways, so, it has been done. Thanks again
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Old 05-26-2006, 05:05 PM   #13
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Re: My car seems to idle rellay rough, and miss badly

try disconnecting battery/ let it sit for ~10 minutes

reconnect, start car.. no accessories.. let it run for 2-3 minutes.. shut it off, turn all accessories on, headlights/etc start it up and repeat

if that fails.. try disconnecting the IAC.. starting the car.. and setting idle, then plugging the IAC back in while its still running.... on that note does it run any better if you disconnect the IAC?

check your TP voltage with the engine off/key on.. should be ~.92-.99 V
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Old 05-27-2006, 11:18 AM   #14
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Re: My car seems to idle rellay rough, and miss badly

Hi again, hanks again for another post. But unfortunately I have done that already too. It was one of the first things I've done. I always do that if I do a swap with a part on the engine. These computers, so I've noticed don't like having new things added till you trick the computer to do its job with the new stuff on it. But again, thanks for the pointer there.
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Old 05-29-2006, 11:07 AM   #15
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Re: My car seems to idle rellay rough, and miss badly

Which computer is in the car now? Is it the J4J1? If its the fox cobra computer, you're going to need an aftermarket ignition to make it run right. Whats it do at idle and how does it run rough? Does it misfire or anything in the high RPMs?
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Old 05-30-2006, 03:15 PM   #16
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Smile Re: My car seems to idle rellay rough, and miss badly

Hi, Yes, the computer is the J4J1. It seems to idle ok, but runs terrible when I step on the gas. I had done a code check, and it says that at least 6 out of 8 cylinders are missing. X's 2 old code reader. It does seem to run a bit better above 3000 rpm, but it isn't right. The way it can be felt. even after a little drive around, it'll stall, and such. Thanks guys.
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Old 05-30-2006, 10:59 PM   #17
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Re: My car seems to idle rellay rough, and miss badly

dose it turn off goin down the road. like when u start to slow down?
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Old 06-01-2006, 12:48 AM   #18
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Re: My car seems to idle rellay rough, and miss badly

its gotta be something either computer, fuel, or ignition related... Have you tried replacing your ignition module? how bout your distributor?
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Old 06-01-2006, 05:06 PM   #19
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Re: My car seems to idle rellay rough, and miss badly

Hi again, all. Yes, it does want to stall when I slow down. And has too. Also, Yes, I have swapped out my ignition module, still acts the same. I also took a fuel sample, in case someone didn't like me and put water in my tank, also swapped out the computer, still the same result. And even did alot of the ignition tests, like checking spark from the coil, distributor, and even all the plugs(1 at a time of course). But thanks for checking to see if I had done that stuff. I'm starting to think it might be a bad ground, as I do have the battery in the rear. I think I might have to run a ground directly to the battery. Just hope its not it though. We'll see. Thanks again all.
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Old 06-01-2006, 05:37 PM   #20
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Re: My car seems to idle rellay rough, and miss badly

A ground could actually be your problem... make sure wherever you grounded it in the trunk, you scraped all the paint off the area where you grounded it. Definitely check all your grounds.
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Old 07-03-2006, 11:16 AM   #21
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Re: My car seems to idle rellay rough, and miss badly

did you try spraying intake cleaner in it my 94 did thatand i sprayed it and it helped some
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Old 07-04-2006, 10:06 AM   #22
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Thumbs down Re: My car seems to idle rellay rough, and miss badly

Hi again. No, I haven't tried doing the throttle cleaner. But I did eventually figure out what has been going on with my ride. I had recently put the battery in the trunk, and routed the positive cable a little wrong(next to the header) And of course you'd know what happens next when high heat and a live wire come in contact with each other. I thought I had fixed the problem, but have soon realized that I have done more damage than first thought. Seems later on, I had to replace the battery, as it acted like a heat soaked starter. Would start with no trouble at all, for the first start of the day, but after that, stop at a store, Etc., it would be really hard to crank. Battery was tested, and failed. Had fried a cell or something. Car had been acting supposedly fine since, but then, it started to feel like it was losing power, and then led to my predicament now. I had noticed under my dash, that I see slight sparks, when I press the clutch down. So I pretty much know, now that its a harness problem, short somewhere under there. I just have to take my time, and not give up on my ride. We'll see what will happen soon. Thanks to all that gave some great tips. And all the provided support.
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