i need some help got my 96 z28 m6 from my grand mother a couple weeks ago. the ses light was on got it checked and it was the p0400 which i know is the egr valve so i figured from sitting about 6 months maybe the computer was acting up so i drove it a little and reset it. everything was fine for a couple hours then ses back on got it checked and now i have p0400 p0172 and p0175 could the bad egr make bank1 and 2 run rich

 

well i found something on another page so tomorrow im going to put the t stat back in and see what happens if it helps ill post it

 

Why did you remove the t'stat?

P0400 = indicates the PCM cycled the EGR valve, and did not see the change in manifold absolut pressure (MAP) that it expected. Could be a valve stuck open (would cause rough idle), EGR passages plugged, EGR valve pintle carboned up, faulty EGR valve, leaking vacuum lines from the manifold to the EGR vacuum solenoid, and/or from the solenoid to the EGR valve. After clearing the code, it isn't unusual for it to take a while for it to come back, because the vehicle must be operated under a very limited set of conditions (throttle position and MAP) before the diagnostic can be run. This code would not be related to a missing thermostat.

P0172 and P0175 indicate the PCM is pulling out fuel, in response to a perceived rich condition, and the control system is about to reach the limit of how much fuel it can subtract. Common causes include (includes only items that would affect both banks):
-high fuel pressure
-fuel in oil
-EVAP canister saturated with fuel
-leaking fuel pressure regulator diaphragm
-intermittent readings from throttle position sensor
-EGR valve stuck open