mtgldr

I have a2010 GT with a very similar issue. In the AM or after many hours of sitting on a cool day at startup the car idles fine. If I accelerate very slowly from 1200 to 1500 RPM I get what I would describe as a sputter or mis. If I accelerate over 1600 it goes away and once the car has gone over 2000 rpm for 15 seconds or so it pretty much never comes back. I can hear it in the exhaust as well. It's like a dripping injector or a plug misfiring. I've cleaned the MAF, changed the fuel filter, replaced the plugs, checked the coil springs in the boots and no change. I did replace one of the plugs with a new plug and it went away for 1 day but come back the next. I have a Steeda CAI, Steeda tune, UDP, flowmaster mufflers, FRP xpipe and CMDelete plugs. It's annoying at best and I can't seems to locate the source either. I was about to buy a coil & injector and start swapping them or take the injectors out and have them flow tested. Sure would like to know the cause before spending the time to swap things 8 times over.

mtgldr

Today I recleaned the TB, removed the motor & mount, cleaned the gears, pulled the coils, flipped the spring connectors and stretched them a litte so they almost extend from the boots. Put it all back together and the stumble is once again gone. Will report back in a couple of days if its gone for good.

I don't think you can really "clean" this TB with it on the car. Clean it then take it off and you'll see what I mean. Also if you remove the TB motor and mount, pay attention to how the return spring goes into the gear. You will need to remove the circular plug in the mount the retension the spring and pull the spring holder outward to lock it into the mount.

Car has 96K on it and there wasn't much "stuff" on the gears but since this its a tight engagement and this car uses the TB for IAC I figured anything on the gears could be a potential issue.

mtgldr

Day 2 - No stumble, all is good. Last time stumble / mis had returned by the second drive cycle on day 1. Forgot to mention, check your COP boots, I found one had gotten hard on one side and I believe that may have also contributed to the condition.

bjbrowder

I never thought of stretching the springs in the coil boots. But I have new Accel coils, wonder if I should try stretching them?

mtgldr

Day 6.... Stumble is back. Only happens at cold start and only happens under 1600 RPM. Once the car is running for > 3 minutes it's gone. THe car actually surges when it stumbles. You would think a mis / stumble would have to be spark or injector related but dang it, it should be consistant then. I thought it may be a "learned" stumble but reflashing didn't change anything. Anyone know enough about these TB's to think it may be caused by the TB? When I cleaned it the shaft was tight, no damage to the gears on the drive, everything felt right. What about the TPS? TPS is learned when replacing one. I'm so frustrated!

mtgldr

Read Roegs & Suicide Bobbs posts regarding the TPS and the readings being erratic. I pulled the TPS. When I initially turned it I felt slight resistance at the closed end of the rotation. I turned it back and forth a few times and it felt very smooth from one end of the rotation to the other. Took some air and blew into the TPS as I turned it. Put it back on the car and did the idle relearn. The car is warmed up at this point so I can't attest to the cold start stumbling but I can say the throttle response when barely touching the pedal is smooth now. I thought it may have been the fingers in the pedal but now I'm thinking it was the TPS?? In the AM I'll see what happens but for the 10 mile idle relearn drive the 900 - 1500 rpm was smoother than it had been.

gregthomas07gt

For what is worth... I'm still fighting this issue and I was told by a Mustang mechanic that this issue on higher mileage cars is almost always related to worn cam bearings causing low oil pressure to the head. The low pressure causes the vct actuators to operate erratically. He said the only way to fix it is new cams and lockouts. I'm afraid to put any more money into it... might just get rid of it.

mtgldr

The car ran fine, no stumbling or hesitation until the morning after I installed UDP, CMDP, washed the motor and installed the new tune. I have been chasing this for 2 months thinking it was the tune because the tuning co was able to greatly reduce the issue by making adjustments in the open / closed loop cycle at startup. I had a hard COP boot, apparently I did not blow all the water off the top of this boot when I washed the motor. The boot was white and hard right where the circular portion seated at the top of the head. I believe the boot was causing a plug not to fire corrrectly. I replaced the plug, boot, stretched the wires and cleaned the TB at the same time, that's the post above. When I cleaned the TB that time I removed the motor and opened and closed the butterflies a lot cleaning the TB. I think that did move the TPS a good bit and thus my issue went away. When I pulled the TPS yesaterday it was very easy to rotate from the idle position to wide open but the TPS can actually rotate past the closed position and that was where most of the resistence was felt. After rotating the TPS thru it's entire range with the air there is no resistence anywhere in the range of motion. If the stumble goes away this time and returns I'll get another TPS. All I touched yesterday was the TPS and nothing else. Fingers crossed it goes away.

Sounds like a good excuse to the wife to get some aftermarket cams though.. LOL

Nuke

Re-install the stock coils. Aftermarket COPs have been rife with problems. Stock COPs are as good as they come and those aftermarket COPs that don't crap out only provide very minor gain on an FI'd engine.

mtgldr

Day 1 - significant difference. The car used to stumble all the way from 1000 to 1400 RPMs and it was enough to make the car lurch. This only lasted for a very short period (15 seconds) and if I accelerated past 1400 it would never stumble. After fooling with the TPS yesterday, today I had 2 very slight hiccups and I could hear it more than feel it. Now it only occurs at 900 rpm, under 900 and over 900 no stumble. Going to leave everything alone for the next 5 days and see if it gets worse. Because I have an auto I can creep the car at low rpms. Just saying in case anyone thought it was a cold clutch.