Hi. I'm experiencing an operational problem over the past 6 mo. Getting this car to idle at 750-800rpm has been a headscratching issue. I am fastidious with the maintenance. However, enging idles up/down between 600-900 rpm just being parked 80% of the time. The engine was recently given a new lease with a new Victor Reinz head gasket replacement showing good compression numbers. Computer was checked as well. The engine will also stall out when decelerating or braking at a light, dropping bellow 400 RPMs and shutting down. I cannot tell if this issue is electrical, or other. Vacuum is good and fuel pressure is stable. Anyone have ideas that might correct this conundrum, I would REALLY appreciate.

BTW> The car was customized with a mustang MAF, 420cc injectors, and upgraded ECU (Jim Wolfe), T3/T4 turbo upgrade, adj FPR, Snow meth kit.