[96-mustang-gt]

After my GT to Cobra motor swap, I am getting these two Diagnostic Trouble Codes:

P0452 Evaporative Emission Control System Pressure Sensor Low Input

P1232 Low Speed Fuel Pump Primary circuit failure

I can clear them using my XCal2 but they do come back.
The car has difficulties to find the right idle speed. Idle speed remains as high as 1500 rpm for a moment until it returns to like 850.
I checked the TPS throttle position sensor signal. That is good, it ranges from 0.94V at shut to 4.63V at WOT.
I also replaced the IAC valve by another one but that did not help.
The idle problems may be related to the fuel pump circuit thing…
What is wrong there, and what steps must I undertake to fix these? Any ideas or comments?

[MARKSSTANG]

Did you ever fix this problem? I recently put in a forged long block from MMR in my mustang, and I am getting the P0452 code as well. My car also feels like it's bucking back and forth when I'm cruising at a constant speed in a steady throttle position. I NEED HELP!