this is an odd one, so bear with me.
2006 GTO, LS, Manual Trans.. BTR PDS stage 3 torque cam, LSA running 8.5PSI, FIC 1000 shorty injectors, Kooks 1 7/8 Long Tube headers with high flow catted mids and magnaflow 3" competition cat back system, BoostDistrict cold air intake with LS7 MAF, DW300C in tank pump, UPP Aux fuel system with external 340 LPH pump triggered at 5PSI, DSX tuning Flex fuel kit.
Tuned July 2019, made 610HP on E85, 576 on 92 octane. Driveability is great, MPG is even decent.
Car lives overnight in the garage (semi-heated) so it's never under about 55-60 degrees even when it's in the 30's outside. startup, even on E85 has been normal. over the last 2-3 weeks, I've started getting a bad surge on cold start, or even if it only sits a couple hours before starting it back up. When it starts, I can blip the throttle and the surge subsides. Checked all vacuum lines etc for leaks, checked all plumbing between the MAF and TB for leaks as well. Nothing. Threw Torque Pro on it since I didn't have my laptop when I went to leave work one day. MAP read good KOEO. fired it up, driving out of the parking lot and when I decel, my Vacuum/boost guage on the dash goes to about 22" vacuum, but the MAP was only showing about 16". did it a few more times to verify. (boost guage has it's own MAP sensor). took off and pulled it to about 5PSI boost and boost read ok on Torque, and after hitting positive pressure, on decel, the MAP would match the Vacuum/boost guage again at 22in vac. Could the MAP sensor possibly be the source of the surge?
attached is the Tune and Log of the cold start when I finally brought the laptop down yesterday.
Thanks