Hi i have a 98 Plymouth Neon 2.0 SOHC. Manual transmission. The car has 134,000 miles. Recently the last 3 months my car began to get poor fuel economy so i changed the spark plugs and wires, air filter etc. full tune up also had the fuel system cleaned out. The problem worsened and began stalling after driving around 15 -20 miles when id get to a stop light or a stop and go situation. Soon after the engine light came on upon taking it to a mechanic i was told my engine was running rich and since then have replaced Up & downstream o2 sensor and also MAP sensor. After replacing sensors engine light is still on and still giving rich code. I have since taking my car to the dealer and was told on these cars the ECU goes bad so upon disconnecting the ECU there was a lot of brownish liquid at the connectors. Could a failed ECU be the cause and the gradual worsening be due to this or is this liquid normal ?

Thanks

Mike