2008 mustang gt.. Running rough, rough idle, loss of power - Ford Mustang Forum

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post #1 of 12 (permalink) Old 01-10-2011 Thread Starter
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2008 mustang gt.. Running rough, rough idle, loss of power

I have a 2008 Mustang GT and it has been running rough all of tthe sudden. The exhaust has a strong smell and it you can hear from the exhaust it sounds like it is missing or something. Does the same thing when I am driving and I left off the gas and the rpms are coming down. Also when I am sitting still and have it out of gear and I give it a quick rev, say to about 2k, the rpms come back down and drop to about 450 or so and it almost sounds like it wants to stall, then they go back to normal. Does this all day, even when for example I am pulling into a parking spot and push in the clutch after letting off the gas and the rpms will drop like I said and then shoot up for a second. The rpms dont move much at idle but the engine kinda vibrates a little. You can tell it is not running right. If I rev it slowly to about 2k or 2.5k the engines starts to vibrate but then stops when i rev higher. I only have 26k miles and have tried a lot already to remedy this. The only thing I have put on the car besides the Cervini body kit is an o/r h-pipe to go with cervini side exhaust and JLT cai with SCT 91 Tune. I am thinkin maybe it is the 02 sensors because i had to replace one when doing the exhaust because it stripped out. It is a different brand the rest. But I am not reading any codes from the PCM. I have cleaned the TB and MAF sensor. It helped a little but not much. What do you guys think?

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post #2 of 12 (permalink) Old 01-10-2011 Thread Starter
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Forgot to mention that the gas milage has dropped some and that it kinda hesitates when taking like from a red light

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post #3 of 12 (permalink) Old 01-11-2011
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I had a somewhat similar problem with my 06 F150 a couple months back. It ran normal but when I came to a stop the rpms would drop low and a couple times it stalled. I checked everything under the hood, cleaned the MAF and it still did it. I went to install a fuel additive and found the gas cap off. Put it on and it's been running fine. I know it's not exactly the same but it's an easy thing to check. If not, I think you should try to reload your tunes and check th o2 sensor to make sure it still hooked up.

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post #4 of 12 (permalink) Old 01-11-2011
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Hi 08BlackBeauty,

Have you been able to bring your vehicle in to your dealership for diagnosis? I would like to see how I can be of assistance. Please PM me your contact info, dealer, VIN and mileage so that I can look into this further.



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post #5 of 12 (permalink) Old 01-11-2011
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Drivabilty problems are usually due to a dirty throttle body. You said you already cleaned it. Try resetting the PCM by disconnecting the negative terminal of the battery for a half an hour. You might also have a clogged fuel filter. Have you ever replaced that? Another cause could be a defective CoP. A detective O2 sensor will usually throw a code.
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post #6 of 12 (permalink) Old 01-11-2011
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mine had been doing this for a while.... I fixed mine by cleaning the throttle body and the MAF sensor.... You can try that and see if it works. If you do try it make sure you buy throttle body cleaner and buy a can of mass air cleaner. Dont use the same thing for both to clean them

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post #7 of 12 (permalink) Old 01-11-2011 Thread Starter
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Hey i appreciate all of the good responses.. This is what I have done so far.. I have cleaned the MAF and the TB, replaced all the 02 sensors, and reset the PCM. It does run better but still has the slight surge in the idle. The idle goes up and down slightly, about every 3 seconds. It also still does the drop in rpms when I rev it a little and let off the gas. I let off the gas from the rev and it drops to about 500 then goes back to normal. Seems like there is a little bit of white lookin smoke comin out of the exhaust (only when sitting idling). Some guy told me he thinks because of the high flow exhaust that the valve timing could be off. I know the rise and drop in idle (from about 700 - 800) is very consistant not irrattic. I dont know what else to do.. Please Help!!
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post #8 of 12 (permalink) Old 01-11-2011
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I had similar issues and was concerned wit was a big job. turns out it was just the TPS (throttle position sensor)... haven't had a problem since I changed that out.

Mine had gotten to the point that it would shut off while shifting (not so much fun while doing 80mph).

Anyway, the damn thing didnt set off the dummy light/throw any codes for the longest time. Thanks to the sh!tcircus on highway, it finally thru a code, made a quick stop at autozone, picked up the part and great ever since.

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post #9 of 12 (permalink) Old 01-11-2011 Thread Starter
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Hey thanx 305GT... Yeah I think tomorrow I am gonna change the TPS and the plugs and see what happens.. I dont know what else to do.. It is still pretty fast and all that but I am a perfectionist when it comes to my car. I cant stand it to run off.. I will keep everyone informed after tomorrow. Thanx for all the replies so far..
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check your plugs. does it sound or feel like your running on less cylinders, when I was shopping for mustangs, one dealer had a problem with the plugs by the cylinder and didn't sound normal and they fixed it.
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I have been fighting the same problem before Christmas and just got it fixed last week. Mine was running so poorly it threw a P0308 code. I replaced the plugs and put a can a Sea Foam in the gas. I all along felt I got a bad tank of gas as it has always run perfect. But I also put in new plugs about the same time. Not sure if it was the Sea Foam or the plugs but it is back to running 100% perfect. Good luck as I know it is not fun.
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post #12 of 12 (permalink) Old 01-13-2011 Thread Starter
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Ok here is an update... I replaced the plugs and the fuel filter and it still does the same thing.. I cleaned the TB and MAF again and nothing.. Now I have a question. I am thinkin, from readin some other forums, that maybe it is my TPS. My question is, Shouldnt your TB be closed all the way when the car? Mine is cracked open a little bit. I can push it closed all the way with my hand when the car is off. Would that maybe mean the TPS is bad? How can I check it to see if is bad? All of the symptoms I have read about with the TPS pretty much match mine.
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