Any codes on dash? Even if not CEL, read it, there maybe a pending code for a clue. Tried starter fluid? (just to determine if it fires for a few seconds then move onto other items to check).

 

Can you be more specific. Does it crank? Does it fire then stop? How long does it stay running?
A video would be helpful.

 

Hi LG,

I hope this helps.

If your 2003 Toyota Highlander is having trouble starting and won't run even after cleaning the throttle body, installing a new air filter, and servicing the air flow sensor, there might be various reasons for this issue:

1. Fuel Delivery Issues: Check the fuel pump, fuel filter, and fuel injectors to ensure proper fuel delivery. A failing fuel pump or clogged fuel filter might prevent the engine from getting enough fuel.
2. Ignition System: Verify the ignition components such as spark plugs, ignition coils, and ignition leads. Faulty ignition components can lead to starting issues or cause the engine to stall.
3. Sensors and Control Units: Other sensors like the crankshaft position sensor, camshaft position sensor, or engine control module might be malfunctioning, affecting the engine's ability to start and run smoothly.
4. Battery and Electrical: Ensure the battery has sufficient charge. Weak or dead batteries can prevent the engine from starting. Also, inspect the alternator to confirm it's charging properly.
5. Exhaust System: A blocked exhaust system could restrict airflow, leading to stalling or lack of power.

Given the complexity of diagnosing these issues, using a diagnostic scanner like the Youcanic scanner to read fault codes from the vehicle's onboard computer can provide valuable information. These fault codes often indicate specific problem areas, helping to pinpoint the underlying issue.
If you've checked these components and the issue persists, consulting a professional mechanic or technician might be the best course of action. They can perform more in-depth diagnostics using specialized tools and equipment to identify and resolve the problem efficiently.

 

Thank you all for the advice. I will check fuel filter next.