1999 Camry -check engine light- EGR

My '99 Camry has 109000 miles on it. About a month ago the check engine light came on and the car started running really bad and stalling at stop lights. My husband took it to the auto parts store to have the code checked. He didn't write down the exact code, but it was something to do with EGR. The guy there said the EGR valve probably just needed cleaning. My brother, who works on his own cars quite a bit, took it off and cleaned it and the car started running fine after that, but two days later the light came back on. Car still ran fine. This time I had the code checked and it was P0401 "EGR flow insufficient". Took it to an independent shop with a very good reputation although I had no experience with them myself. They said no parts needed replacing, but that the EGR ports were clogged and they cleaned those out. I didn't get 10 miles before the light came back on. Took it back - the mechanic said he found a hose that wasn't completely connected. This time the car went 125 miles before the light came on again. The car still runs fine. I'm getting really aggravated with this darn light and tired of taking it back there - it's a 30 minute trip and my husband has to take off work to drive me back and forth. I hate to take it to the dealership because frankly I just don't trust them, but is that the only way I'm going to get this thing fixed? Does anyone have any ideas what might be wrong? My husband says to just ignore it and clear the code right before it has to go for inspection in the spring, but that worries me.

It sounds like the EGR valve was cleaned and the car is no longer stalling. So, it's possible that the Check engine light is for something else.
If you get the same code it's more than likely the EGR Vacuum Switching Valve (VSV). This is actually the most common cause of the PO401 code.
This is the Toyota recommended diagnostic order of testing for the PO401 code.
1. EGR valve stuck closed.
2. EGR Vacuum Switching Valve (VSV).
3. EGR VSV open circuit.
4. EGR valve position sensor open or short circuit.
5. EGR valve position sensor.
6. ECM

The code is still the same - I had it rechecked when it came back on. Can a mechanic tell if a particular part is bad? Or do they just have to replace parts until they get the right one. The place I took it to is supposed to be one of the best Toyota/Honda specialists in town and they seemed pretty sure that no parts needed replacing. Can they be sure of that?

They can't be sure if they don't test the parts! There are continuity and ground tests and vacuum tests for the EGR and the VSV. Check the vacuum hoses for tightness, cracks or holes. The readings vary by engine type. Do you have a 4 or 6 cylinder engine? Your library may have a Chiltons or Haynes manual for your car and it illustrates the procedures. They're straight forward. The factory manuals for your car (I have them) are more detailed but I'm looking at a Chiltons manual and it covers your problem fairly well for the do-it-yourselfer. Also, check the electrical connectors for tightness.

It's a 4 cylinder. Thanks. That's what I needed to know. I wasn't sure if there was a way to actually test the parts individually or if it was just guesswork. When they said no parts needed replacing I assumed that meant they had tested them and found them to be OK. I really don't know anything about car repair and would be afraid to try anything myself. And I'm sure I don't have the equipment I would need to test anything. I'm just trying to get a little bit educated about what might be wrong with it and why a supposedly qualified mechanic can't find the problem after having the car for two whole days. I'm thinking I'm just going to have to take it somewhere else - probably the dealer - ugh. I have to take it there for a new seat belt retractor anyway. Thanks again.

Because most qualified mechanics are not willing to use a multimeter, or a vacuum gauge. ;)