Tausif123

As Protholl mentioned above, walnut blasting is the process of using a fine abrasive (Ground Walnut Shells) to blast off the carbon buildup on the air intake valves on Direct Injection engines like the IS250. It requires removing the intake manifold to gain access to the valves and so I had it done for $500 by a shop that mostly does German cars.

I never had the smell ever again and the engine runs better after the walnut blasting. Makes me think the rotten egg smell is caused by the burning of carbon buildup at high RPMs.

2013FSport

iTrader: (2)

The smell is caused by incomplete combustion and the catalytic converter attempting to reduce the hydrocarbon emissions. Typically from running to rich which occurs during open loop operation like startup and WOT where the O2 sensor data is ignored by the ECU. During normal driving (closed loop operation) the air fuel ratio is roughly 14.7:1 and the cats can burn the unburned fuel from the mix. In closed loop operation, the O2 sensors are monitored and fueling ratio of 14.7:1 is maintained by the ECU.
When accelerating briskly, the AFR can jump down to 13 and even 12.0:1, but the engine isn't efficient enough to burn 100% of the fuel and it makes it stink as the cats get a work out removing the excess hydrocarbons.

Note: this is a generalization... Closed loop does monitor / maintain other AFR states beyond 14.7:1 which typically occur at steady state throttle conditions, i.e. while making adjustments to obtain that stoichiometric 14.7:1 ratio where the combustion process consumes most of the fuel and the CAT's work most efficiently.

As for the wall nut shell blasting, it cleans up the airstream into the engine so it can burn the fuel more efficiently and maintain an equal fuel ratio in all cylinders. The design of the combustion chamber and pistons are pretty good but when the intake is occluded, the fuel and air do not mix efficiently and raw fuel is spit out of the head and down the exhaust manifold into the CAT, the added work the CAT does to convert the unburned fuel makes it stink.

Adding to the above. When the MAF is dirty, the ECU doesn't know exactly how much air is entering the engine. As a result the AFR is off and the cats work overtime and the exhaust can stink.

Tag: JJD952

ELexis

Interested in knowing, if you removed the fabric like filter attached to the underneath of air intake box cover, after drilling the additional holes in air filter box;

2013FSport

iTrader: (2)

Random comment: I clean this carbon mesh filter every time the MAF gets cleaned by back spraying it with a LOT of MAF clean shot through from the intake pipe side.

ELexis

I know a lot of owners have removed this to obtain better airflow when updating intake, and thought perhaps by removing ths "pre-filter", might negatively impact engine performance. I had asked dealership about it's function, and was told by service advisor that it was part of the emissions system, and was anon-maintenance / serviced item. Not much of a through explanation.