I've got a 91 Accord DX with about 90,000 miles on it. I went to have it inspected this year and it failed becssue the NOx was high. Started doing some troubleshooting and it seems the EGR is not opening up at speeds above idle like it should. However, when you first open the throttle, it opens momentarily and then closes. I have a Haynes book and have gone through all the troubleshooting offered. Everything checks out correctly. Here is a list of the things I've done:

Valve -
Cleaned the EGR Valve, operates freely - OK
Tested for holding vacuum - OK
Replaced it with another one - no change

EGR control -
Checked the black/yellow wire at the control box for power - OK
Checked for vacuum on line 16 when EGR control solonoid is powered on, (jumped terminals A+ & B-), vacuum increases within 1 second - OK
Examined control box and verified vacuum getting to it, and hoses in good shape - OK

ECU -
When I try to get the codes from the ECU, I jump the diagnostic connecter and the check engine light just stays on when the key is in the II position.
Had another ECU so swapped it out on the off chance it might change something - no change
The Check Engine light acts normally when you key on, and when the car is running it is OFF.

Is it normal for the Check Engine light to stay on when trying to pull codes?
Is there another component that will have an effect on how the computer controls the EGR? The O2 sensor was changed out a couple of years ago.

I'm at a loss as to what's next. The car seems to run fine but won't pass inspection so I'm on borrowed time until I get the ticket. Anyone have any ideas?

 

When you jumper the SCS connector (& turn ON the key) to read codes, it's normal for the CEL to stay ON if there's no stored error codes.

Have you checked the EGR passageways (in the intake manifold) for being plugged up with carbon crud?