Chevrolet: EGR?, chev truck, rubber gasket

Question
I have a 1989 Chev truck with a 350 and throttle body fuel injection.  The truck started fine and ran smoothly when cold, but once it warmed up it ran rough, especially at idle (I know the EGR shouldn't operate then).  I found the EGR diaphram was leaking so badly the hose may as well have been open to the air.  I found another that seemed to function at the wreckers and installed it.  Now it still runs smooth when cold, but worse than before when it warms up, even having less power on the highway. I suspect this is when the temperature sensor allows the EGR to operate.  Is it possible that the fuel injection has made some incorrect adjustments to the mixture, or what do you think the problem might be?  The EGR that was on the motor and the one I bought have the two small holes besides the main two, but they aren't present on the intake.

Answer
Hi Roy, did you check the valve itself to see if it leaked after it opened it may be sticking open, causing it to run rough. You can check the EGR system by putting a flat piece of metal and a thin rubber gasket over the hole where the EGR valve is, blocking if off. Then plug the hose. If it is ok then the valve is faulty. You can have it put on a anlizer to check for a faulty map sensor or low vacuum to the sensor. I hope this helps you, if you need more help just let me know. Regards, Keith.