1988 Fuel injection car was running and slowly over one week the idle dropped lower and lower and now won't start. It still has spark at every plug and plugs get wet with fuel. What could have happened?

Check compression; timing belt may have jumped. Check crankshaft belt gear & shaft for key wear, mazda had a special washer set & replacement bolt
with different torque spec. If shaft key way wore, have heard of guy welding it as repair.