DTC Code P0401-EGR Flow Insufficient_PLEASE HELP

[hillre]

Good Morning! I've a 1996 Grand Prix (SE), 3.1 engine, automatic transmission with 210,000 miles. My Service Engine Light is coming on intermittently. I purchased a Actron scan tool (CP9135 at Pep Boys) to detect the DTC. The code found was a P0401 code, which is defined as "EGR Flow Insufficient." However, the vehicle is running fine while the engine light is on. I noticed that one of my exhaust muffler has a hole in the top of it. Would this create a P0401 code? Can anyone tell me the most likely source of this problem? My online research has revealed that it may be a clogged EGR Valve, clogged ports beneath the throttle body, clogged upper and or lower intake manifold. Thus far, I took off the EGR valve and cleaned it. The Service Engine Light is still coming on every few days or so.
Should I remove the throttle body to check the ports (I'm not really familiar with removing throttle bodies, also, when removing throttle bodies, do you have to drain the radiator?, I think I read this in my Haynes auto manual, but not sure it's necessary for removing the throttle body). I really don't want to purchase a new EGR valve unless I'm 100% sure it's if defective. My understanding is that a special scan tool is required to determine if a Digital EGR valve is faulty. The last thing I want to do is go to a dealership and aske them for assistance. I would appreciate any advice on this aggravating problem. Thanks for taking time to read this! Happy Holidays to You/Family!
Thanks

[GTP Dad]

The egr is probably dirty although with that many miles it could be bad. Remove the valve and spray the underside with throttle body cleaner. This will remove the carbon and should allow it to operate better. Also check the passageways into the engine. They too can become clogged with carbon and cause similar problems. They can be cleaned in the same manner but you may have to remove the upper part of the manifold to do the job. A brass cleaning brush like one used to clean gun barrels will help to remove the carbon after it is sprayed with cleaner. If this doesn't work a new valve will be the next step. As for the muffler, that will not cause these problem.