Hi.
I recently bought an 83 Celica via ebay. Celica's that I had driven in the past had a lot of power (for a 4 cylinder) and got good mpg.
Mine has 85k original, drives well and seems to be in really good condition. But its not running as smooth or operating as well as my friend's higher miles, more beat up Celica. I thought a tune up might do the trick; I've adjusted the timing and rpm. Replaced the sparkplugs, wires, distributor, rotor, oil, oil filter, fuel filter, and added fuel injector cleaner. The car runs better but still feels like it should be getting more power and still only gets 20.5 mpg city highway combo (I understand I should be getting around 30). Now I'm thinking maybe it's the cat, it just passed admissions but I'm running out of ideas and it kinda feels like a clogged cat (rumbling at times, slow take offs, and funky rpm behaviors).
Does anyone have a good clogged cat test or think I should try to try something else? Like I said, I'm running low on ideas,
TIA