think that your timing belt tensioner may have run out of tension and allowed a tooth to go by...notice how the kit has a tensioner...this is just a guess,...but the only other guess would be a fuel pressure regulator~
It being a '97 with who-knows how many miles, it could also be a clogged catalytic converter. Protege's also have a known issue with the intake hose developing splits too. You'd need to take it off completely and do a full inspection.
Looking for a Used Protege in your area?
CarGurus has 324 nationwide Protege listings and the tools to find you a great deal.
Search Mazda Protege Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Mazda Protege Experts