I have a cadillac deville 98 and it turns off when idling or slowing down such as when parking the car. On long road trips with no stops it runs fine.

Gas Filter Clogged ?

Check Fuel Pressure at motor with a gauge

Take the gauge on the road trip-tie to a wiper
so you can see it

Any check lights on?

Your loosing fuel or air metering data

Have Crank Sensor checked with a scope

Check Exhaust Converter

Check Fuel trim on road test

Check your fluid level and belt for tension and adjust or replaced as needed.

Do this frist and then if the miss is still there have the spark plugs and plug wires replaced.

This problem is commonly caused by a dirty automatic idle speed control valve and throttle valve. Buy a can of throttle valve cleaner (do not use carburetor spray cleaner!) from NAPA or Carquest (made by CRC chemicals) and spray it into the air intake while the engine is running, use up about 1/2 the can, engine will try to stall hold the speed up, shut it down and let it soak for 30 minutes, restart and blow out the remaining fluid, shut it down and disconnect the negative battery cable for 5 Min's to reset the base idle control

when your car stalls by turning left or right, usually a loose or a glazed belt is suspected. reason being is that the pump is being put under a load by the power steering piston. making belt slip because it needs more torque to spin pulley. also draws more current, so check idle speed and spark plugs.

I A C motor small part on throttle body ,controls idle mixture when they fail at idle the engine "hunts" for proper air/fuel mixture . when defective it causes o2 sensors and TPS to compete to set an idle thus the up n down effect.. auto wreckers if your broke new from your local parts store....dealer to much 1 plug in two bolts for most applications

sounds like an ignition module or coil pack issue.happened to my friends 98 caddy sls.after a road trip to dallas,tx,then back to atlanta.

dee if the linkage is binding first, clean the throttle body and lubricate all moving parts if this doesn't solve it an accellerator cable may need replacing

check diagnostic codes.could possibly be crankshaft and camshaft position sensor

Reverse flush the cooling system and put in fresh antifreeze to -20. (20 below zero). If that doesn't help, replace the thermostat.

have throttle position switch checked and idle control valve checked.