Lumpy engine start and idle

[Dm85]

Just out of interest I put your symptoms into chat GPT IA and this is what it told me:

A lumpy or rough idle on a cold start in a VW T6 (or any vehicle) can be caused by several potential issues. Here are some common ones:

1. Dirty or Faulty Idle Air Control Valve (IACV): The IACV controls the amount of air bypassing the throttle body during idle. If it’s clogged or malfunctioning, it can cause uneven idling, especially when the engine is cold.
2. Vacuum Leaks: Any leaks in the vacuum hoses can cause unmetered air to enter the engine, disrupting the air-fuel mixture. This can make the engine run rough at idle, particularly when it's cold and the engine management system is adjusting for higher idle speeds.
3. Fuel Delivery Issues: A clogged fuel injector or a failing fuel pump can cause uneven fuel delivery, leading to rough idling. The cold start process requires a richer fuel mixture, so any irregularity in fuel flow could cause a rough idle until the engine warms up and the system compensates.
4. Ignition System Problems: Worn or dirty spark plugs, faulty ignition coils, or a weak spark can cause misfires, leading to a lumpy idle. This is especially noticeable when the engine is cold and the spark plugs might not fire as efficiently.
5. Temperature Sensor Malfunction: The engine’s coolant temperature sensor helps the ECU adjust the fuel-air mixture during cold starts. If this sensor is faulty, the engine might receive the wrong air-fuel mixture, causing rough idling.
6. Air Intake or Throttle Body Issues: If the throttle body is dirty or the air intake system is clogged, it can cause a rough idle due to inconsistent airflow into the engine.
7. EGR Valve Issues: A malfunctioning EGR (Exhaust Gas Recirculation) valve can affect the engine’s performance by allowing too much exhaust gas back into the intake, disrupting combustion, especially at idle.
8. Low-Quality or Incorrect Fuel: Using poor-quality fuel or the wrong type of fuel for your engine can also cause rough idling, especially when cold.
9. Engine Control Unit (ECU) Software Issues: In rare cases, the vehicle's ECU may need to be updated or reset to correct idle problems.

If you’ve noticed that the rough idle improves as the engine warms up, it’s likely a cold-start issue, and these are the most common culprits. A scan for error codes with a diagnostic tool can help pinpoint any specific problem.

I wonder how long it will be before AI will know more than MMI

 

[shaiboyuk]

Just out of interest I put your symptoms into chat GPT IA and this is what it told

Lol don't trust "IA" or even AI lol

@mmi is the boss here haha

 

[CJW]

Worn or dirty spark plugs,

Mmmmm….. lovely AI sludge.

 

[shaiboyuk]

So the garage done another compression test, say they don't do them when engine is cold, as vw states "Engine oil temperature approx. 80°C."
But this is the new results....




They saying they need to do more tests, but looking like they need to claim on extended warranty for a new engine....

Keep asking for original compression results, but seems to be avoided. Asked about DPF and EGR to be checked, again no comment about...
I had a gut feeling when they done the HPFS that it wouldn't help. And now I've got a similar feeling about them saying it looks like its going to need a new engine...

This plus they seem in no rush to get it tested and passed to claim on warranty. ARGH

Whats labour time for replacing an engine? a lot of things need swapped over? and how does it normally work with getting DVLA to update V5C? Will it affect resale of van (losing love for it)?