87 Crown Vic sputtering

A friend of mine has a 1987 Crown Victoria (guessing over 120K miles on it) and lately he noticed that when he drives on the highway over 65mph it runs great but when the mph is lowered to say 50 and below either in slow moving traffic or around town it seems to sputter and miss. Wondering if this might be a fuel filter/fuel line issue? Where to start to self-diagnos and repair the issue before heading to a shop.

I don’t know if that year had fuel injection or side draft carburettors. Start with all the tune up things, first (actually, routine maintenance): Fuel filter, air filter, pcv valve, spark plugs and wires, distributor cap and rotor. Check the ignition timing (including the advance, vacuum and mechanical). Check for excess play in the timing chain. Consult with Mr. Haynes about details.