2000 Dodge stratus running rough. Changed plugs. Ran good for about 5 miles. Then car startrd running rough againwith check engine light flashing on and off. What is the problem?

SOURCE: Dodge stratus R/T 2002 antifreeze problem(antifreeze coming out the cap)

First the "service engine soon" light is a manufacturer installed reminder for you to get an oil change or other pre-determined maintenance service done. It is different than the "check engine" light which indicates a sensor malfunction. Secondly, when the engine is cold the thermostat is closed and the antifreeze or coolant is not circulating. The cooling system is a closed system and the tank that the cap is on is not an overflow tank but rather an expansion tank. This tank allows for the expanding coolant that is now hot to leave the engine coolant jackets, that won't expand, into a tank that can expand slightly. When your engine got to normal operating temp., aka.. hot, the thermostat opened allowing coolant to circulate and fill the expansion tank probably over flowing with the cap off. This is a normal operation for your car.

SOURCE: car stopped running on highway and wouldn't

you should check engine compression if you can. its possible you have a bent valve.

SOURCE: I have a 2001 Dodge Ram 1500 5.2L,

The plenum problem should not affect compression tests. It allows oil to get sucked into the intake and will cause carbon buildup, plug fouling, and pinging. If you have zero compression on a cylinder, it is usually a valve problem. Even a burned piston will make some compression, unless it has a big hole in the middle.
Sorry, but if your compression results are to be trusted (and it seems they are), then you have to tear a head off to find the problem, or at least get a borescope in it.

SOURCE: 2001 Dodge Stratus SE MIL light on problem

sometimes you cant trust those dummy lights, i would keep driving it or have your car parked and turned off and turn you key on to aux. and turn off and the turn on aux again, and the ck engine light will blink count the blinks and spaces and the car will give you a code and if there is something wrong, then the code is were you want to start, look on line for the code or get a 2001 dodge stratus manual that will tell you as well and then go from there

SOURCE: 2004 Dodge Intrepid Check Engine Light & Bad Fuel Mileage

If it has never had plugs changed, i would suggest it. It can make a big difference.

Labor time is .8 hrs + 6 plugs = $80 - $150.

Take your car to a parts place and they will usually check and clear your light for free.

Firestone likes to up-sell everything, $650 is way too much for a basic tune up.