I've got an A-code 289 that was taken from a 67 mustang that I rebuilt and installed recently. The engine had clearly been redone before as it was already .30 overbore and had forged .30 over pistons to match. The cylinder bores were in great shape (no excessive taper or wear) and I just quickly cleaned the bores with a 120 grit ball hone. The cam bearings were replaced at my local machine shop and my main bearings were installed and measured for oil clearance. I'm using the factory ford heads that are ported and polished with pinned rocker studs. I'm using a comp XE 262H with the 351w firing order and Trick Flow TFS-16942-16 valve springs. The ignition resistor wire has been bypassed for my 12v ready-to-run electronic distributor. Finally, it's topped off with a Weiand Street Warrior intake and 600cfm Edelbrock AVS2 carburetor.
I have run the flat-tappet cam break-in process with no perceived issues. The valvetrain has no clatter and the rockers kept their adjustment. The oil pressure was a steady 60-65psi at break-in rpms and also had no overheating issues. I've since run it in park and attempted to work on my timing and carb adjustments. The motor sounds great and revs very responsively and clean.
However, I'm having some issues finalizing my tune. I cannot get the car to idle below 1100 rpm while sitting in park and the engine stalls under load. The engine will sometimes die when turning the wheel and using the power steering pump in park. When shifted into gear (C4 auto), I have the give it a lot of throttle to keep the engine from stalling. Additionally, the engine will stall when braking to a stop. With a vacuum gauge attached while idling at 1100 rpm, it quickly fluctuates from about 16-19 in of Hg.
I've tried retiming the engine, making more adjustments to the carb, plugging all of the vacuum ports and spraying carb cleaner around the intake and carb base gasket. Checked my fuel pressure and spark plug gaps. I'm not sure where to go from here. Any advice would be appreciated!