Always liked this body style, so finally bought a MkIII, but it came with a spun rod bearing. I have an unusual problem following a complete rebuild and reinstall. Engine starts easily and idles smoothly. It rpms smoothly up to 1800 rpm at which point it stalls as though the ignition had been shut off. I don't have a scanner for this old a car. Looking for advice before I buy another scanner. Have built many performance and stock engines in my life, but am much more a builder than an overall mechanic. Don't think the problem is mechanical. Any advice?