I have a problem that just started. The idle goes from fast to slow..but the check engine light does not come on. Changed the fuel filter, cleaned the injectors, blew out the engine, and it stopped. Turned the engine off, then started it again..and the same problem was back. What sensor is located next to the O2 sensor on the exhaust manifold. I am guessing the O2 sensor ha the green on it? Any ideas would be greatly appreciated.