Problem: Starts hard when cold, must floor accelerator, blows blue-gray smoke for about five seconds after start. Will not start at all when hot; just cranks and barely fires. Acts like it's flooded. Runs fine when it does start, although idle speed is high (@1,100 rpm on the brakes, as when at a red light; unloaded idle speed fluctuates between 2,500 and 500, before settling at about 1,200; previously, idled at 600-700). Occasional bursts of rpm to 3,000-3,500, not dependent on speed (happening on daily basis now; did have eight or ten such incidents in the last couple of months). Does not "down idle" after reaching operating temperature. Fuel mileage off about 20%. Some slight fuel leakage around #3 injector (due to overpressure/excess flow in fuel rail?).
Recent work: Replaced water pump and belt tensioner 10 days ago (Thu). Currently running cooling system flush and water; will replace with coolant/water mix later this week. Cleaned engine at U-Wash-It last Sunday (allowed engine to cool @30min before; U-W-I is less than two miles from the house). Next oil change due in 500 miles; not losing oil. Problem began on Tuesday after engine wash, no problems on Sunday or Monday.
Troubleshooting to date: Replaced spark plugs (due replacement in two weeks anyway); plugs slightly fouled, probably due to excessively rich mix. Checked all accessible electrical and vacuum connections; all appear dry and tight. Serpentine belt tension good; belt scheduled for replacement after I get the current problem corrected. Unseated injectors and cleaned in place with carburetor cleaner, also cleaned injector bores; unable to remove fuel rail due to frozen throttle cable bracket bolts (plan to replace all injector seals after I get the bolts broken loose at a machine shop). Fuel line connections good. Air filter dry and reasonably clean. Cleaned throttle body and butterfly valve with carburetor cleaner. Both air filter and fuel filter scheduled for replacement next month.
Items eliminated: Internal engine (rings, valves, etc.) since engine runs relatively smoothly (no missing or stumbling). Plugs, plug wires, coils, etc. Fuel feed system (except as noted below).
Possible problems, based on information from the Haynes repair book for this model: Oxygen sensor on exhaust manifold. Fuel pressure regulator on fuel rail.
Anything else I should look at? I'm leaning toward a bad O2 sensor as the culprit, based on my limited understanding of the fuel injector system and the information in the Haynes, but at $70+ for a replacement part, I'd rather not unless absolutely necessary - can't afford it until after payday anyway.