I've actually helping friend with a '96 Lexus ES300. I'm posting here since the car is essentially a '96 Camry V6. My problem is code 0401-EGR flow insufficient.

I have removed the EGR valve and thoroughly scraped and cleaned it out as much as possible.

I tested the EGR valve with a hand-held vacuum pump and can see the vacuum diaphragm moving when vacuum is applied.

With the EGR valve installed and the engine running at idle, I can apply vacuum with my hand pump, and the engine starts running very rough, like it wants to stall. From what I've read, this is normal.

I have removed and tested the EGR VSV and checked it in accordance with the factory service manual. The resistance across both terminals is within factory specs. When direct voltage is applied, I can hear and feel it operating. When I blow air through in accordance with the factory service manual, it functions as it should with and without voltage applied. So I assume this part is functional.

I have replaced all vacuum hoses associated the EGR system.

The vacuum modulator was replaced this morning. I didn't change it, the friend did. They are certain they got it on correctly, so I will say that it's on right and all connections are proper.

Code 0401 has returned yet again after about 35 miles of driving.

When I last played with it yesterday, it seemed to me that the issue is in the vacuum modulator. It gets vacuum from the two hoses on the back side, but never draws vacuum from the single hose on the front.

I've instructed them to spray some throttle body cleaner into the throttle body through those two vacuum lines with the engine running.

What other options do I have at this point?

 

These systems vary with year.

Does the EGR valve has a position sensor. It would be mounted on top of the valve and signal the locations of the valve to the computer.

Also check for a exhaust temperature sensor mounted on the EGR assembly.

If the system has these they can fail.

If the modulator has three hoses, two may connect to the throttle body, one to the EGR valve. The VSV connects the hose from the modulator diaphragm to the EGR diaphragm. There may not be a lot of air flow compared to a line connected to the throttle body and any air flow would only occur when the VSV was turned on. The flow would also be 2-way.