If you're lucky the CEL is probably just a knock sensor code.
Things you can do: change plugs w/NGKs, new plug wires, air filter, fuel filter, check valve covers and replace (easy 20 minute job), new PCV valve, seafoam treatment, clean the throttle body.
If the timing belt is overdue I would get on that when you get a chance. Replace all the timing components, pulleys, tensioner, belt, water pump. And while the timing belt is off replace the cam and crank seals, reseal the oil pump and check the screws, replace camshaft support o-rings.
You should be good to go then!