Only P0401 code and egr passages are clear

[joncheryl]

I sincerely apologize if the answer is obvious but I searched here and other places and couldn't find what I was looking for.

 

2001 Suburban 5.3L with only the code P0401 - Insufficient Flow through EGR system. From reading online, usually this is cause by carbon buildup in the egr passages or at the manifold. On my truck, it's all clear. If I manually actuate the EGR valve at idle (I don't have a two way scanner), the engine runs really rough and will stall. If the EGR valve wiring was bad, I'm pretty sure I'd get another code, like "incorrect pintle position" or something of that nature. The only thing I can think of is that perhaps the way the computer calculates EGR flow is bad but I don't know how EGR flow is calculated (MAP/MAF sensors???) and I would think if sensors were bad, I'd have another code like "engine too lean/rich". I moved and need this to pass emissions in Utah. But even more than that, I want to just know what's going on.

 

Any ideas?