Regarding the Rough Running & Check Engine Light:
* Spark Plugs and Wires: Worn or fouled spark plugs and/or damaged ignition wires are common culprits for misfires, leading to rough running. The check engine light will likely register a misfire code (P0300 or a specific cylinder misfire code like P0301, P0302, etc.).
* Ignition Coils: A failing ignition coil can cause misfires in one or more cylinders.
* Mass Airflow Sensor (MAF) Sensor: A dirty or faulty MAF sensor provides incorrect air/fuel mixture readings to the engine's computer, leading to rough running.
* Throttle Body: While you cleaned the IAC valve, the throttle body itself might be dirty or sticky, affecting idle and overall engine performance.
* Oxygen Sensor(s): Faulty oxygen sensors can cause a rich or lean condition, affecting fuel delivery and leading to rough running.
* PCV Valve: A clogged PCV (Positive Crankcase Ventilation) valve can cause excessive crankcase pressure, leading to various engine issues, including rough running.
* Fuel Injectors: Clogged or faulty fuel injectors can cause a cylinder to misfire or run lean.
* Engine Computer Issues: Less common but possible, a problem with the engine control module (ECM) could be causing the misfire and rough running.
Regarding Coolant Loss:
This is a serious issue and needs immediate attention. Low coolant level, especially with a rough-running engine, could indicate:
* Head Gasket Leak: This is a significant concern. A blown head gasket can allow coolant to leak into the cylinders (leading to white smoke from the exhaust and potentially misfires) or into the oil (creating a milky oil).
* Cracked Cylinder Head: A crack in the cylinder head can allow coolant to leak internally or externally.
* Radiator Leak: A leak in the radiator itself is a possibility, though less likely to directly cause misfires.
* Water Pump Leak: A failing water pump could leak coolant.
What to Do:
1. Get the Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to read the codes stored in the engine computer. This will give you a much better idea of what the check engine light is indicating.
2. Inspect for Obvious Leaks: Carefully inspect the engine bay for any visible coolant leaks, paying close attention to the radiator, hoses, water pump, and cylinder head.
3. Check the Oil: Check the oil level and color. If the oil is milky or frothy, it strongly suggests a head gasket leak.
4. Address the Coolant Leak First: This is the priority. Driving with low coolant can cause catastrophic engine damage.
5. Based on DTCs and Visual Inspection: Once you have the codes and have assessed the coolant situation, you can start troubleshooting the specific issues identified. Replacing spark plugs and wires, cleaning the throttle body, or replacing sensors may be necessary.
Important Note: If you are not comfortable performing these checks and repairs yourself, take your vehicle to a qualified mechanic immediately. Ignoring the coolant leak can lead to severe and expensive engine damage. The rough running is a secondary problem compared to the potential engine damage from the coolant loss.
