2007 mustang gt sluggish performance
 

Hi All,

i need help with my 2007 mustang gt.
i own it just over a year now and these are the parts/mods i ve done so far:

-k&n typhoon cold air intake
-airaid throttle body spacer
-Throttle body cleaned
-DNA motoring end pipes
-New O2 sensors
-New ignition coils
-New spark plugs
-new fuel filter
-all fuel injectors cleaned
-rebuilt transmission
-no cats

the car has 277k km ( mainly highway driving) cylinders compression test was done and all were around 155-165psi. The car suddenly (after the transmission was rebuilt and placed back) started to perform poorly, struggling to accelerate, especially when in low rpms and when cruising almost like it’s suffocating.. idling is also somewhat rough sometimes. The car also runs super reach. If i step on the pedal, it wakes up and runs amazing! (It’s stage 2 tuned)
I checked everything i thought might be a cause (spark plugs, coils, injectors, maf, vacuum leaks) but everything seems good. The car has no codes whatsoever.
the strange thing is that the car was running great before the transmission rebuilt and as soon as i got it back these problems started. I am wondering if they screwed something up when they were putting the transmission back or the pcm is acting up.
I am running out of ideas what to look further, so any direction you can give me would be really appreciated.

Can anyone please help?

what is a stage 2 tune?

The O2 sensor wires are routed on the outside of the transmission. The harnesses must be disconnected from the transmission mounting point and each O2 disconnected from their wire harness to drop the transmission. A lot of times the wires get pinched/broken or just completely mangled. . Do you have a code scanner with Live data capabilities? I have a feeling one or both O2 sensors are not working correctly. You can also get underneath the car and follow the O2 sensor wires from the sensors, up and around the transmission to where they disappear above the transmission.

thank you very much for your reply.
Engine was tuned/remapped for optimal performance with the mods that i stated above, so i guess that is stage 2 tuned as its pretty aggressive with cats delete and full straight pipes.
with regards to O2 I totally agree with you and still believe it must something yo do with that. I had codes which are O2 related when they put transmission back (p2195, p2197, p2198) but then the guy, who tunned my car before, said he “reprogrammed” it so there are no codes any more but the car still tuns like crap. All O2 sensors are new as we suspected this was the issue, but we did not check the wiring, which they could easily mess up when putting transmission as you mentioned.
i will try to inspect all the wires and see if i get anywhere with this.
Once again, thank you so much for your input.

UPDATE:
so i checked the O2 sensors and wires as suggested by @Derf00 and everything seemed to be in order. Then i disconnected both upstream sensors and boom, the car runs like a champ!! I have no codes either so whilst i am happy that it’s all back to normal, i am also worried why there is no engine light with codes..?? Maybe this program guy completely deleted my O2 sensors if that’s possible??
anyway at the moment, i am happy that i can drive my mustang finally with no hesitation, sputter and stalling.. 😃

Glad your car is running good now!

With proper turning, it is possible to delete the O2 sensors. Normally when you do that you are supposed to unplug or remove them. I don't know what happens if you leave them plugged in when they are supposed to be deleted. Maybe what you experienced? Maybe someone with experience can chime in.

Don't some tuners "turn off" the upstream or downstream 02 sensors in order to run catless pipes? Seems like you'd probably want to disconnect the downstream ones though since you'd get different readings after the cats but I could be wrong on that

LATEST UPDATE:
so the engine light did come eventually and triggered both bank 1 and 2 upstream O2s as they were disconnected.
i started reading more forums and saw that one guys had a similar issue and he said plugs were wrongly connected after the tranny job. I then swap the connectors bank 1 with bank 2 and plugged them in. Boooom!! The car is back to life!! So the mechanics who rebuilt my transmission plugged O2 sensors in the wrong connectors!! Anyway i am so happy that i finally came to the bottom of it and once again thank you Derf00 so much for the right direction!!