Eggy smell

[Norwichdaz]

Hi guys,

Its the 2nd time happend in 2 months now, after a sh!tty 45 min city drive in traffic etc starts to get an eggy smell inside the cab.
The engine doesn't over heat or run any differently, but engine light came on (came on 2mths ago and went in a few days)
But say I turn it off then on it struggles slightly.

"Google" says if struggles to turn on once hot could possibly be high pressure fuel pump?

I mean anyone else with that kinda smell would say the cat converter.

Seen somewhere a possible bad o2 sensor too?

Going to obvs get it scanned asap.
 

[Snoopy]

As you say Eggy smell is often a poorly regulated catalyst converter or a running issue causing the cat to smell. A scan will give you more indications.

[Norwichdaz]

Scanned today same things that have come up for a while for some reason...

The mechanic said he thought could be injectors possibly flooding the cylinders and damaging the cat? Mentioned walnut blasting..

Didnt .mention a thing about a faulty o2 sensor etc ..hmmm

As I say runs no different, doesn't seem sluggish, just that smell in heavy traffic and the odd engine light .

[Norwichdaz]

[JSYGTI]

The same thing happened to my GTI last year, but in my case, the performance was hit too.

After cleaning the injectors and replacing the plugs, the mechanic replaced the pressure control valve (I think that’s what it’s called) and all was well.

I was getting the same P0172 code that you’ve got.

Hope you get it sorted.

[Norwichdaz]

Ah ok mate cheers, 

Yeh around 6 mths ago have had all new plugs,coils and pcv tbf.

I know bit of a chore with the injectors if wanted to properly check them.

As I say just if sat around in city traffic, bit random.

Im guessing a bottle of cataclean is jist "gimicky" ? Or worth a shot or running one thru?

[JSYGTI]

To be honest, I’d give it a shot. In fact, I may still do that.

[Norwichdaz]

Okey doke,  the mechanic also said as done 160k , to walnut blasting, but not much change from £450, not sure how that would stop the smell in heavy traffic etc tho? Lol

[JSYGTI]

I’m no mechanic, but walnut blasting does seem to be clutching at straws. Do you have another mechanic you can try?

[Nino]

Walnut blasting probably isn’t aimed at the smell itself mate it’s more about fixing one of the likely causes behind it.

On these direct injection GTIs, the intake valves get heavily carboned up over time because fuel never washes over them. At 160k, chances are the valves are pretty coked up unless it’s been done before.

That buildup can cause:
- rough hot starts
- poor airflow
- uneven combustion/misfires
- rich running (your P0172 code)
- excess unburnt fuel going into the cat

That last bit is what often causes the rotten egg/sulphur smell in traffic because the cat gets overloaded and starts producing hydrogen sulphide.

So the mechanic’s probably thinking:
carbon buildup → engine running rich/poor combustion → cat overheating/smelling.

Walnut blasting won’t magically “fix” a dead cat or faulty injector if one’s already gone bad, but on a high mileage it’s definitely not clutching at straws either it’s proper maintenance and could improve the hot start issue too.

Personally though, before spending £450, I’d still want:
- fuel trims checked
- injector balance/leak test
- HPFP pressure checked
- live O2 sensor readings checked

because a leaking injector or failing pressure control valve could also explain the rich code and egg smell.

Finally, if it was me, I would only use a Garage that really knows what they are doing and have the injectors ultrasonic cleaned if they are good or replaced if they are not as well as the injector seats checked for leaks.