Could it be the air pump or is more likely to something else 1985 Corvette runs rough when cold and check engine light comes on?

A rough running 1985 Corvette when cold, accompanied by a check engine light, is highly unlikely to be caused by the air pump (also known as the air injection pump). The air pump's role is to pump air into the exhaust system to help burn off unspent hydrocarbons, primarily during warm-up. While a malfunctioning air pump *could* contribute to emissions issues that eventually trigger the check engine light, it's not a primary suspect for a rough cold start.

More likely culprits include:

* Fuel delivery problems: This is a very common cause of rough running, especially when cold. Consider:

* Fuel filter: A clogged fuel filter restricts fuel flow, particularly problematic when the fuel is cold and more viscous.

* Fuel pump: A weak or failing fuel pump might not provide sufficient pressure when cold.

* Fuel injectors: Clogged or malfunctioning fuel injectors can lead to inconsistent fuel delivery.

* Throttle body: Dirt or deposits in the throttle body can affect the air/fuel mixture. Cleaning it is often a simple fix.

* Ignition system issues:

* Spark plugs/wires: Worn or fouled spark plugs and faulty ignition wires are prime suspects for misfires, leading to rough running.

* Distributor cap and rotor: These components can degrade over time, affecting spark delivery.

* Ignition coil: A weak coil won't produce the necessary spark voltage.

* Temperature sensor: An inaccurate coolant temperature sensor (CTS) will give the computer wrong information about engine temperature, leading to poor fuel mixture calculations. This is highly likely to cause rough running and a check engine light when cold.

* Mass Airflow Sensor (MAF): If your Corvette has a MAF sensor, a dirty or faulty sensor can also lead to incorrect fuel mixture calculations.

How to proceed:

1. Read the codes: The check engine light is your best friend here. Get the diagnostic trouble codes (DTCs) read using a code reader or from a mechanic. This will pinpoint the specific problem area.

2. Basic checks: Start with the simpler and cheaper checks:

* Inspect spark plugs and wires: Look for corrosion, cracks, or excessive wear.

* Check the fuel filter: If it hasn't been replaced recently, it's a good idea to change it.

3. Professional diagnosis: If the simple checks don't reveal the problem, a mechanic with experience in older Corvettes is your best bet. They have the tools and knowledge to properly diagnose and repair the issue.

Ignoring the check engine light is unwise. Continuing to drive with a malfunctioning system can cause further damage. Get it diagnosed and repaired promptly.