Rough running at 50+ mph

I have a 2000 Toyota Corolla with about 170,000 miles. It idles rough and at about 50-55 mph it loses power and runs very poorly, like it is not banging on all cylinders.

I think you just diagnosed your own problem. If its not running on all cylinders…you need to get it running on all cylinders first. If you arent running on all 4 cylinders it makes no difference how it behaves at any speed. Sounds like this Toyota needs a simple tune up

Spark Plugs, Air Filter, and depending upon what type of ignition system it has… those parts as well.

If you have a regular distributor…then you need to replace the distributor Cap and Rotor, Spark Plug Wires and Spark Plugs. If you dont know when any of these were last changed it wouldnt hurt you to replace them so you know where you are with Tune Up Service… I usually replace everything EXCEPT the spark plug wires…and see what I get… if it still doesnt run on all 4 then I will replace the wires.

Some newer Toyotas no longer use a distributor and spark plug wires…just open your hood to see what type of ignition system is used on this Corrolla…Pretty simple. I bet simple tune up service will get this Toy running on all 4 again… Thats about itski…