I have a Low RPM (2000-2500ish @ 80km or 50mph) stumble/hesitation. Scanner reads lean on the car when the stumbles happening.

Many people complain about the EGR messing up and getting clogged or not working correctly from time to time. But suppose you had a clogged CAT, this would then increase the backpressure before the cat meaning any exhaust gasses which would be recirculated would be under much more pressure than usual. This would cause probably a lean condition in the car since its shoving more air than it was designed to back into the system...
Does this make any sense? My EGR appears to work fine and stalls the car when i press it. But the fact that my stumble seems to only happen when the cars warmer (i think, never really run my car cold at 50mph), and the warmer the car is the more apparent the stumble is. If the cats clogged and its heating up way hotter than usual it would also mean an even bigger increase in pressure resulting in an even more apprent stumble.

This "theory" of mine seems to account for my symptoms to a T. Anyone have any input on this? Perhaps my understanding of the EGR valve is slightly off... but I think it just rapidly opens and closes to let an amount of air in... having a larger than usual pressure would mean much more air is going through than anticipated....

 

I have the same stumble but no cat. Sorry

 

Excessive backpressure in the exhaust would force more EXHAUST to be recycled into the intake manifold, not more "air". It would be just the opposite.... exhuast is already burned and has no oxygen in it.... it would displace the room in the combustion chambers the incoming air would normally occupy, the MAF sensor would detect the recuced air flow, fuel should be regulated correctly. A clogged cat will just kill power.

 

I also have a similar stumble with no cat. Seems to only happen under light throttle, never get it WOT.

TTT