Cold Start Issues: Troubleshooting Engine Problems

When the engine is warm, it doesn't start as smoothly as one would expect, and if you don't hold the ignition key in the "start" position for about half a second, the engine might even stall.

Of course, everything is subjective, and I'm also a mechanic who can "feel" his engine (specifically, the crankshaft bearings) - but to put it simply / to describe it better...

When you turn the key, the engine starts immediately - but somehow you get the feeling that the last spark from the last cylinder is firing very "hard" and "unevenly" - like a delayed "misfire," even though three cylinders have already started working. This "hard" last spark (during the starting process) sometimes also causes the engine to immediately shut off again - even though you were expecting it to run.

I've now gotten into the habit of holding the ignition key a half-second longer than just the usual quick "click" and immediately releasing it. Since then, it hasn't turned off on me at least.

My engine is a PD DPF 2.0 TDI BMM (DSG KCU) Variant, manufactured in 2008.
4300 km, 15g ash mass, previously operated exclusively with ARAL Ultimate fuel.
I was used to a better starting performance from my previous cars thanks to the premium gasoline. You only had to briefly turn the ignition key, and the engine would start smoothly.
Approximately 10,000 kilometers ago, this car was exhibiting the same issue.
However, I've never owned a car that was consistently and exclusively run on ARAL Ultimate fuel, right down to the last kilometer. I know that ARAL also mixes a bunch of junk (water?/emulsifiers?) into the Ultimate fuel to...
being able to lower the price. Could this now be my "comeuppance"?

What engine data could I log or monitor to help with...?
Are you experiencing poor starting behavior ("misfire" during startup)?

Hello,

Please check the coolant temperature in measurement block 7 of the engine control unit using VCDS to ensure it is plausible and not several degrees too high when the engine is warm.

Best regards, Rainer.

Yes, I think the coolant temperature seems reasonable based on what I'm seeing.

Here are 5 logs from the sections I drove today.
Something very similar happens almost every day for me.

Before each engine start, I have enabled the logging of data points 067, 007, and 010.

Der erste Log ist der erste Start am heutigen Tage nach 17Std. Standing time - cold.
The other logs are from the individual sections of the route that I started and drove after short, and sometimes longer, breaks.
a: To the VW dealer.
b: to the store.
c: to school.
d: to the swimming pool.
e: From work to home.

As with the demo effect, today everything went well except for the last launch (e).
"in the green zone." Only on the last start today did I encounter such a nasty problem again.
"Loud rattling" when starting, which shakes the entire car.

I don't have any water in the oil.
My oil now has 12,000 km on it, and besides a tiny bit of fuel residue, there's nothing to complain about in its appearance - definitely no water or coolant contamination.