I have a 1985 Frebird.
The older style EGR assembly.
I knew my
EGR Metal tubes to MPFI were good
My EGR was still functional & good (no rubber bladder air leaks).
The rubber hoses seemed to be good (I replaced them earlier).
I knew of a few problem areas.
My "T" vacuum hose junction broke, I replaced it & it seemed to be ok.

Yet, I kept getting the EGR SES light action.
Drove me up a wall.
Even swapped on another EGR valve to test "theory".
SES light still came on.

Yesterday, while fiddling with my Blazer 3.4 swap, I needed to check some wiring on my Firebird, to match how to do it on the Blazer swap.

I also looked at my "T" fitting in the hoses.

I dug out all my vacuum hoses from the swaps.
I found another "T" vacuum line fitting.

I changed all the 5 1/6" vacuum hosing & routing around the EGR metal hoses to the MPFI unit.
Made all smooth bends, etc.

SES LIGHT NEVER HAS COME ON, I IDLE SMOOTHER, I THINK CAR IDLES SMOOTHER, COLD.

I followed my own advice.
Vacuum hoses cause all sorts of problems until all vacuum signals are correct & no leaks.

I had a closed air passage (caused by exhaust manifold heat melting, twisting) on that "T" vacuum line fitting I bought.
Replaced that "T" fitting, problem solved.

My cost, FREE!
Hope this helps ya solve your EGR problems.
Again
FREE FIX,
I didn't even disconnect the battery to remove the SES code.