2014 Avalon Hybrid Choppy Engine

[Eaglewingmd]

I have a 2014 Toyota Avalon Hybrid. With a cold engine the engine starts up and runs choppy, or tough, as if there is a misfire. One time I got a code which said that cylinder 4 was misfiring. I have investigated possible caseus and replaced all spark plugs. Same problem. The checked the coils and the misfire code did not move to another cyliinder. And I have replaced the Camshaft sensor. Nothing fixes it.
This happens with a cold engine, but it also happens at a stop light on start up, after and then the engine shuts down.
Although it doesn't happen 100% it's frequency is increasing. It is close to 80% of start ups.
Any suggestions?

[igor@af]

You've already addressed the spark plugs, ignition coils, and camshaft sensor, which are common causes. Here are a few other potential issues to look into:

Fuel injectors: A clogged or malfunctioning fuel injector could cause a cylinder misfire. You may want to check and clean the injectors or replace them if necessary.

Intake manifold gasket: A vacuum leak in the intake manifold gasket could lead to misfires. Inspect the gasket for any signs of wear or damage, and replace it if needed.

Ignition control module: The ignition control module manages the ignition process and can cause misfires if it's not functioning properly. Check the module for any issues and consider replacing it if needed.

EGR valve: A faulty Exhaust Gas Recirculation (EGR) valve can lead to misfires. Inspect the EGR valve and clean it if it's dirty. Replace it if it's not functioning correctly.

Oxygen sensor: A malfunctioning oxygen sensor can cause poor fuel mixture and misfires. Check the sensor's readings and replace it if necessary.

Mass Air Flow (MAF) sensor: A dirty or faulty MAF sensor can cause improper air-fuel mixture, leading to misfires. Clean the sensor or replace it if necessary.

Engine coolant temperature sensor: If the engine coolant temperature sensor is faulty, it can cause the engine to run rich or lean, leading to misfires. Check the sensor and replace it if necessary.

Compression issues: Low compression in a cylinder can cause misfires. Perform a compression test to check the health of the engine's cylinders.