Sputtering low RPM when engine warms
 

01 Mustang GT (Auto Tranny)

I was on my way back from a 100 mile trip and near the end of the trip the car started to sputter a slight bit when I would give it gas when I came to a stop sign but would clear up once I was up to speed.

Over the course of a few weeks it progressively got worse, the sputtering seemed like it was only under low RPMs but if I tried to give it a very small bit of gas just to get rolling to get up to speed I can keep the sputtering to a minimum also if I shift threw the gears manually (auto tranny) once about 2500 to 3000 RPM it would clear a bit and I could gradually give it a little more gas. The car feels like it is dragging or holding back, the sputtering makes my power go to nothing but you can feel it wanting to come threw esp if you get the RPMs higher. Over drive has helped me a little bit also.

It is a very inconsistent sputter and does not sputter when I would start the car for the first time in the day on a cold engine, I can go to the gas station but on the way back it will start sputtering once the engine became warm. The heater/AC makes it worse (my car never ran any differently before when the ac or heater was on but now it does)

THINGS REPLACED:

TPS
MAF
IAC
EGR
Air Filter
Spark Plugs
2 Coils
Fuel Filter
Fuel Pump
Catalytic Converters

Sprayed the engine bay with starting fluid to check for vacuum leaks and found nothing, I am out of options and have no clue what to try next.

Anyone have this problem before? I have been doing this for 2 months now and this is my 7th Mustang. Never been stumped like this or had this on any other Mustang.

Have you changed the coolant sensor?

No I have not changed that never seen anything on it. I did the alternator last night still no change on that either.

What ever it is has to be temp related since it acts great when cold but like a sputtering power lose fool once drove for 5 minutes. The coolant sensor can cause all this?

It also has to be something that can go out progressively. The car got worse and worse with the sputtering each time I drove it to work.

Just replaced the Coolant Temp Sensor and used seafoam spray this time directly threw the intake. Took each plug and coil off and cleaned them again and regapped them, still not time for new plugs I just did a full tune up a little over a month ago.

Replaced the PCV valve too since I rigged that one on a while back from my V6 Mustang.

I will see how she does tomorrow when I head into work and will provide update if it was that Coolant Temp Sensor or not.

No change - Anyone on this???????

Check for codes.

It has never thrown a code.

Not even a stored code? The CEL doesn't always get triggered, even on an OBDII system. My Thunderbird once had a misfire that went undetected, even by my scan-tool.

I have gotten them read just 2 days ago by the chance it would have and nothing.

Seriously NO ONE knows??????????????????????