2007 mustang gt sluggish performance

bk2024

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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 MAF sensor
-New ignition coils
-New spark plugs
-new fuel filter
-new fuel pressure regulator
-all fuel injectors cleaned
-rebuilt transmission
-no cats
-professionally tuned (stage 2)

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 rich. 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 reset the pcm (by connecting negative and posotove terminals) and still the same, car is struggling to accelerate and rough idle, engine spluttering..I also ordered the new fuel pump, so that's my last resort.
I am running out of ideas what to look further, so any direction you can give me would be really appreciated.
 

Dino Dino Bambino

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You might want to check the O2 sensor wiring harnesses. They can easily be pinched when the tranny is reinstalled and there's a good chance the wiring could be damaged.

You might also want to lose the throttle body spacer. It's a waste of space (pun intended) and money. Either sell it in eBay or use it as a paperweight.
 

JC SSP

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Wouldn’t the pinched harness set an O2 code?
 

Miker

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Manual or auto?
Seems like I read something needs to be set correctly if a flywheel is pulled.
 

bk2024

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It’s an auto. I disconnect both upstream O2 sensors and boom the car runs amazing. But.. the engine light on with codes for both banks O2 sensors. Can i drive like that? It is very difficult to follow the wires as they are deep on top of the transmission.
 

bk2024

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You might want to check the O2 sensor wiring harnesses. They can easily be pinched when the tranny is reinstalled and there's a good chance the wiring could be damaged.

You might also want to lose the throttle body spacer. It's a waste of space (pun intended) and money. Either sell it in eBay or use it as a paperweight.
Guys, i just fixed the problem!! Dino Dino Bambino was absolutely right!! So after i disconnected both O2 sensors the car was running much better but this triggered the codes. So all i did was just swap the O2 connectors and boom!! The car started purring like before!! No codes and super smooth ride. So the mechanics who fixed my tranny clearly messed up the wiring and plugged the O2s wrong! So just a simple swap (bank 1 and 2 plugs) solved the problem.
Lesson learned (to check always the logical thing first and question the last job/move that trIggered this issue in the first place) after changing so many parts and hours of breaking my head!! And yeah i guess i will keep my useless waste of spacer, at least it looks good under the hood..
Thank you so much for you guide and direction.
 

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