Experiencing a check engine light in your vehicle can be concerning, especially when accompanied by unusual engine behavior. If you’re noticing your RPMs hanging high after releasing the accelerator, particularly around 2600 RPM, and your fuel economy seems to be declining, you’re right to investigate further before heading to a mechanic. These symptoms, combined with a persistent check engine light even after basic maintenance like spark plug replacement, suggest underlying issues that can often be diagnosed with the help of an OBD2 scanner.
One common symptom associated with a check engine light and these performance issues is an engine RPM that doesn’t immediately drop when you lift your foot off the gas pedal. This “RPM hanging” can last for a few seconds, as you’ve described, and it can indeed contribute to decreased fuel efficiency. The fact that you’ve already changed your spark plugs and the problem persists indicates that the root cause likely lies elsewhere.
To effectively diagnose this, using an OBD2 scanner to read real-time data is an excellent next step. Specifically, monitoring short-term and long-term fuel trim data can provide valuable insights. Fuel trim values indicate how the engine’s computer is adjusting the fuel mixture to compensate for either lean or rich conditions. Abnormal fuel trim readings can point towards vacuum leaks, faulty sensors (like Mass Air Flow (MAF) sensor or oxygen sensors), or issues within the fuel delivery system itself.
Vacuum leaks are a frequent culprit for RPM hanging and check engine lights. A leak in the intake system can introduce unmetered air into the engine, disrupting the air-fuel ratio and causing the engine to run lean. This can lead to both the RPM hanging issue and the illumination of the check engine light. Carefully inspect vacuum hoses and intake manifold gaskets for any signs of cracks, looseness, or damage.
Sensor malfunctions can also lead to these symptoms. For instance, a malfunctioning MAF sensor might provide incorrect airflow readings, leading to improper fuel delivery and RPM fluctuations. Similarly, oxygen sensors play a crucial role in monitoring exhaust gases and adjusting fuel trim. Faulty readings from these sensors can throw off the engine’s computer and trigger a check engine light, along with performance issues.
Once your OBD2 scanner arrives, pay close attention to the fuel trim readings. Significantly positive long-term fuel trim values often suggest a lean condition, potentially due to a vacuum leak. Negative values might indicate a rich condition, possibly related to fuel injector issues or sensor problems. The real-time data provided by the scanner, along with a systematic approach to checking for vacuum leaks and sensor functionality, will be invaluable in pinpointing the cause of your Cub Cadet’s check engine light and RPM hanging problem, allowing for a more targeted and cost-effective repair.
