Q: I have 2004 Mercury Sable. It randomly stalls, after putting in gas, on hot days, will start after resting AC goes hot during buck

Hi Sandy. Thanks for all the information - it’s very helpful to initially provide some technical advice. It appears as if you might have a few different things going on with your Mercury Sable. First, in regards to the engine vibrations and stalling, that’s likely due to air / fuel ratio components being damaged or dirty (such as the mass air flow sensor or EGR valve). It’s also possible that you have an electrical harness that monitors and controls these components that is loose or even a loose vacuum line (which might explain the inconsistent operation). In regards to the AC blowing cool without a problem and hot when there are issues, that may indicate an issue with the AC compressor or the pulley that drives it. When your AC runs, it draws a tremendous amount of power from the engine to operate this system. Existing problems with the engine will be enhanced considerably when the AC is on. When an AC compressor or the pulley’s are damaged, or wearing out, this type of symptom may occur. I think the best advice we can offer is to have a professional mobile mechanic come to your location to complete an onsite inspection, so they can determine what’s causing the check engine light, as that’s an indication that the ECU has detected a fault that needs attention - and will provide the mechanic with a starting point to diagnose your problems.