EGR woes

1999 Tacoma DLX ext cab 2wd auto 2.4l

When I got the truck the check engine light was on. Scanned, 0420, bad cat. Muffler shop tried to convince me I had a Cali emissions truck and had a cat built into the exhaust manifold. After doing research, found out it wasn't a Cali truck, there WAS NO cat on the exhaust manifold. So I bought a new Magnaflow stainless case bolt-in cat for $100 and swapped it out. Code went away, more power, I was happy.

Until 100 miles later, when the CEL came back on.

Back to Auto Zone, scan, this time code 0402, excessive flow detected on EGR system. Time to break out the Haynes manual.

Tested the EGR valve with a vacuum pump, it bogged the engine with vacuum and idle returned to normal when vacuum was released. So the EGR valve's working.

Tested the Vacuum Switching Valve, held vacuum with no current, free flow with current. Pass.

Replaced all of the vacuum lines with 3mm high performance silicone line. The old lines looked fine but at this point it was a cheap way to rule out a hose leak.

Cleaned the Vacuum Modulator filter. The manual didn't show a test for the Modulator, but found an article that said if I blew into port Q while blocking off ports P and R, it should pass air through the filter. No air passed at all. Hoping I found the problem, I replaced the Modulator with a new one (which I tested first), reset the computer and crossed my fingers. Ran great for the next 100 miles, then threw the CEL again.

The only other part I can test is the EGR Temperature Sensor, and I really hope that's not the problem because that's a $180 part from what I've found.

When I took the lower hose off of the Vacuum Modulator, I did get quite a bit of carbon dust out of it. I'm wondering if the line off of the EGR to the Modulator could be clogged. I'm hesitant to remove the EGR, however, because apparently the studs that hold it on are prone to breaking. I at least want to have some new studs and gaskets on hand before taking the EGR valve off to clean it.

At this point I'm open to suggestions. Heck, I'd bypass the whole system if I could, but not sure how to go about it on a computerized system. I've read numerous complaints about how the mechanical emissions system is the weak point on this engine. I do know that if I'm driving with the a/c on (August in Texas gets warm) I have no power, and it's very sluggish until the engine warms up to operating temps.

So, any help on the matter would be greatly appreciated, whether it's a test I haven't done, advice on r/r of the EGR, cleaning tips, or a way to eliminate the whole mess, even if it does upset the EPA. I just want my truck to run right and get decent mileage.