I have a 1997 Eclipse RS non turbo 2.0L. Some of the symptoms I'm having are: The motor runs rough for 5 seconds when the motor is cold and first started in mornings, sometimes hard to start. When the motor warms up to operating temperature the idle begins rise and fall between 800 and 400 RPM randomly. When im driving the car and I floor the gas pedal it will start hesitating and backfire through the throttle body. I threw a P301 and P302 misfire code, reset the ECM and it hasn't been throwing any codes since but the problem is still there. I have replaced throttle position sensor, coil pack, spark plugs, spark plug wires, ECM, and fuel filter, but the problem is still there. Spark plugs are not carbon fouled. Fuel pressure is high, compression is high in all cylinders. Car has 134000 miles on it. Another thing to note is that the fuel relay went out on it so the fuel pump is hooked directly to the battery with a toggle switch to turn the pump on and off. So basically there is no fuel pump relay at all. If anyone has any suggestions about what the problem could be I would greatly appreciate the input.

 

couple questions...did the problem start before or after the relay popped? have you cleaned the throttle body? what kind of gas do you run? anything over 10% ethanol can cause massive carbon build up and even crappy fuels 10% ethanol and lower can cause this, my suggestion would be to try cleaning the throttle body with a approved cleaner and run a can of sea foam through it in the gas tank, if that dont solve the problem take it to a mechanic

 

Not sure if the problem started before or after the relay went out. When I bought the car the fuel pump was already bypassed from the relay. I actually took the throttle body off and cleaned it really good and replaced the gasket, also cleaned the IAC sensor. I run Chevron premium gas in my car, always. Tried running Chevron Techron full concentrate full system cleaner with the gas. Do you think Seafoam would be better than Techron full concentrate? Do you know if one of the wires that goes to the fuel relay has to be grounded?

 

Check your timing.

 

Is the timing belt adjustable? Would the car still run if the timing was off?

 

Just check the timing. Either that or you have a valvetrain issue.

 

When you say valvetrain issue do you mean valves in particular? Ill check the timing first.

 

Yes..

 

Another thing to note is when I cycle key on and off three times It flashes some check engine codes: 12, 42, 62, 55. Does anyone know what these codes represent?

 

That makes no sense. Are you sure you're reading the codes correctly?