unrated83

I have a 1993 ford fiesta 1.1. It will not idle. The air filter is covered in oil and the hose going to the oil breather gets coated with a sludge(light brown color). Once its on the highway it does fine but, you come to a stop and it winds up and down then dies. Going to replace air filter. Pulled the plugs they look ok. Also had about 3 liters of diesel go through the system. Sprayed carb cleaner in the throttle body? or whatever you like to call it. Also trying fuel injector cleaner. the rockers looked quite sludged when looking through the oil fill. Doesn't burn oil(not any that I have noticed) black but still full. The car only has to last a year and doesn't go long distances or driven for very long. Any tips to make this car last let me know please.