Sounds like the ignition switch is fine. You need to get a mity vac and check all of the vacuum system. Faulty HVAC or lock systems can and will affect the engine shut off. It appears you have a vacuum leak somewhere,

The mitiy vac can also tell you about the health of your vaccum system and brake booster.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D