misfire at idle when warm - Ford Mustang Forum
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post #1 of 4 (permalink) Old 07-12-2019 Thread Starter
NAs197's Avatar
Joined: Sep 2016
Posts: 78
misfire at idle when warm

Hi All, I have been battling this problem with my 07 GT for the past couple months. When I first start the car it idles fine, but as it warms up it starts to have a misfire at idle (the engine shakes and I can feel it in my seat/steering wheel so I believe that's a misfire). When it misfires the idle drops down a bit. The car has not stalled on me. I feel no loss of power and under any type of load it runs perfectly smooth. i do think though that my mpg's have gone down. I have done the below:

No codes
Spark plugs were replaced 17k ago before the issue occurred
Just cleaned throttle body, MAF, Air intake and ran fuel injector cleaner
Seems to settle a bit when I turn the AC on but still has issues
Will settle a bit when I give it gas but rough idle will return
Did idle relearn
Cleaned crud around negative terminal but some of that blue stuff is still there
Unplugged VCT sensors, started car still and still had the idle issue

Mechanic hooked up a smoke machine to find leaks, thought that certain injectors may have been leaking and replaced some seals. He also drove the car while hooked up to his computer and didn't find an issue with any coils. I told my mechanic to check the alternator and he didn't say it was bad so i'm assuming it's fine. Also when the car sits for a month it starts up immediately like a brand new car would so i feel like it's good. Haven't checked the TPS sensor yet but I doubt that's it because I feel like that wouldn't cause the engine to shake/misfire.

I have datalogged the car and If someone who understands that stuff can/wants to read it please send me a message with your email and I'll send it right over. Any help is greatly appreciated. I am trying to sell the car and it would really help if I could get this issue fixed before selling it.

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post #2 of 4 (permalink) Old 07-13-2019
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Joined: Jan 2011
Location: Central Massachusetts
Posts: 8,945
Originally Posted by NAs197 View Post
. . . I have datalogged the car and If someone who understands that stuff can/wants to read it . . . . .

I don't (know how to read it well enough) but Lito does -- you might shoot him an e-mail at [email protected] to see if he can help you and how much he would charge

| 2010 GT coupe | Daily Driver with some Steeda and GT500 take-off stuff for the occasional track day
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post #3 of 4 (permalink) Old 07-30-2019
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Joined: Apr 2014
Location: Birmingham
Posts: 1,929
Feel free to shoot me your log along with a full list of all of your mods. Also check your coil boots and spark plugs even though you did plugs 17k miles ago.

[email protected]

2007 Mustang GT 5-speed 3.31 gears, Hidden Hitch Receiver, Barton Short Throw, JBA LTs, Borla Touring Axle Back, and Lito tuned SCT X4. BMR SP009, KYB Shocks & Struts, J&M CC plates, J&M LCAs. 4 Piston Brembos
255/45ZR18 front 295/40ZR18 rear
Department of Boost GT450 with 2011 GT500 M122, TB, & CAI | 13/14 GT500 HE & IWP | GT500 dual pumps | FRPP 52lb | CMS Stage 2 Blower Cams | Comp Springs & Retainers | AEM boost & wideband | 8 rib conversion | Track Spec GT500 Vents
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post #4 of 4 (permalink) Old 07-30-2019
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Joined: Jun 2016
Location: Seattle
Posts: 930
If you still have a misfire on a hot engine, it might be a temp sensor not sending the correct info to the computer. Or it could be a fuel supply issue caused by a weak pump or partially clogged fuel filters. I'd have the fuel pressure check on cold start and on engine warm up.
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