1999 chevy tahoe

(code300 random misfire)truck has bad hesitations went start off and at crusing speeds.I have replaced sparkplus& wires, rotorcap & button. coil &
modular, new distributor.Do you have any other advise
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debbiediane wrote:

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sure,, heres what you do. throw about 4 bottles of STP injector cleaner in the gas tank the next time you get gas. dont fill the tank more than half, that way you get a nice concentration of the stuff running past the injector nozzles. put the cleaner in first and then the gas do'd it will mix up in the tank'. If you do a lot of non highway driving then take it out on the expressway and drive it for about 20 miles to blow the pipes out.
now for the egr valve. I dont have a book on you vech but the egr valve is on the top side of the engine and its suppposed to shoot a little exhaust gas into the motor when it needs it. That exhaust gas is a little dirty so it sometimes clogs up the valve. Get yourself a manual for the vehicle, it tells you how the do these things where they are and pictures of what they look like. They all look a little different from maker to maker and from model to model.
I moved this to your own topic. First off here is what your codes mean...
P0147 O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 3)
P0300 Random/Multiple Cylinder Misfire Detected
My guess would be you need a new Oxygen sensor.
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