3rd Gen EGR System & Service Cost at 9K+ if Head Gasket Blows

Actually this is not correct. A stuck open egr valve can cause rough idling and stalling - it is designed to be closed and no flow at idle, low rpm and wide open throttle. Your egr valve was stuck open or more likely the head gasket was already bad. HG leaks are subtle and often confused with other misfire causes at first.

For that money they are selling you a rebuilt motor, probably with a new short block to take care of the low tension rings - the cause of gen3 oil consumption and carbon build up.

Dealers won't do a straight hg job because they often fail quickly. Not always if the hg is caught early but too many don't recognize the symptoms or believe the hundreds of posts that cold start stumbles are egr related.

The reality is hg parts are about $500 and labor is often $1,000 to $1,500. Again pro shops don't want to risk it and be forced to fix it again under warranty if it fails in a year.

Other options are professionally rebuilt engines shipped to your local independent shop for installed cost of $3,500 to $5k.

Others buy a used in Japan low mile JDM engine for $1,000 to $1,500 plus a $1,500 install. In Japan these engines were used through 2021 with all major design problems addressed by 2016 including gasket design, intake, egr valve and ecu software for water pump logic.

 

In other words, the criminals at your Toyota Stealership are saying that they're going to charge quadruple of what an honest local mechanic would charge you to do the repairs. Don't waste your time talking to those con artists!

Also, as @ChapmanF often points out we don't have absolute proof that a clogged EGR will cause a blown headgasket, it could just be Toyota screwing up their design and not creating enough strength where the head gasket fails between cylinder 1 and 2 because they were trying to fit a larger engine into such a small engine compartment starting in 2010 in US and 2009 in Europe...

Also we do know a clogged EGR will make an engine run hotter, which could be a contributing factor to head gasket failure.

 

I don't think I know that at all. I'm pretty sure an engine with a clogged EGR will run at a coolant temperature around 85 to 95 ℃ pretty much like the same engine with working EGR, as regulated by the engine thermostat and fans, which handle bigger differences in heat load every time you go up or down a hill.

The thing that EGR is known to affect (because that's what it's for) is the milliseconds-scale peak temperature inside the mass of burning charge during the power stroke. That's not to be confused with the steady temperature of the massive aluminum engine block and head, the gasket sandwiched tightly between them, and the coolant and oil circulating through.

On the other hand, literature can be found linking subnormal EGR flow to detonation, and detonation to head gasket damage, so there is a possible causal path there.