After highway driving your car dies starts fine but when you put it in gear it dies?

If your car starts fine but dies when you put it in gear, it could be due to several issues. Common culprits include a malfunctioning idle air control valve, a problem with the fuel system such as a clogged fuel filter or failing fuel pump, or issues with the transmission. Additionally, a vacuum leak or a faulty sensor could also cause stalling under load. It's advisable to have a mechanic diagnose the issue to ensure a proper fix.