1994 Toyota Previa Q&A

1994 Toyota Previa Question: 1994 precia dx with 165000 miles failed 25 miles/hr HC smog check. Any fix idea!

I have new spark plugs, new wires, new distributor cap, new air filter, oil/filter changed. Could It be that the Throttle position sensor is worn out and affecting my timing advance and increase my HC. The NoX is below avg. -
Answer 1
Do you know if your engine is reaching proper running temp.? thermostat could be stuck open.Or temp sensor itself could be giving the PCM false reading.Have you been getting less than normal fuel mileage from it? -
Comment 1
The 2 times I brought the car in, I drove it about 1!2 hr on the frwy and used a tankful of premium gas. It idles ok and mileage seems ok. Is it possible that the throttle position sensor is worn and giving an incorrect timing to the engine, thus higher HC? -
Comment 2
Not likely,throttle POSITION sensor merely tells the computer how hard your getting into the gas , the PCM uses that sensor INPUT along with INPUTS from MAP,CRANK ,CAM,IAT(INTAKE AIR TEMP)AND COOLANT TEMP SENSOR etc..Temperature is a large factor in proper combustion.cooler combustion temps will also lower your NOx. -