I have a 99 Chev S-10, 4-cyl, which has no power. I suspect that the EGR valve is clogged or bad -- I have looked (& looked ...) but can not find it. Can someone please direct me in the right direction!!!

I think on a 1999 it is internal.

do a tuneup.

The EGR valve on the 2.2L engine is located at the rear of the engine, upper corner, driver side.

If the EGR valve is causing the engine to lack power, it will set a code in the OBDII and illuminate the "Service Engine Soon" light. It's always best to correctly troubleshoot it before pouring money into it needlessly. Autozone and Advance Auto will retrieve codes for free. Write them down and post the results here. How many miles on the vehicle? What is the repair history such as spark plugs, wires, distributor cap, rotor, fuel pump, fuel filter etc.?

I have new wires, plugs, & coil packs. The vehicle has 112K. I have looked the entire engine over to include the top rear of the engine, but no EGR valve. There is no room on the back of the engine to house the valve -- only about a 3" clearance between engine and fire wall. If I am not mistaken, I believe that my vehicle has a linear EGR valve -- not vacuum controlled. The Haynes book show the valve on top of the TBI, but once again, I see nothing which looks like an EGR valve.

That's correct, it is a linear EGR valve. From the images I have, it appears to be on the driver side of the engine, close to the bulkhead, (firewall). It may have a tube connected to it that runs to the exhaust manifold, or a tube that runs to the intake manifold, depending on exactly where and how it is mounted. The electrical connector on the valve has four wires: Black, Brown, Red, and Grey.