This morning i replaced my EGR valve on a count of the car idling funny and stalling sometimes at red lights. These all seemed to be symptoms of an EGR Valve. Well after the I replaced the EGR valve the symptoms were worse. The rpms would go haywire. Bouncing all over the place and the car would buck ( not bad, but i could feel it) and then stall out. Now my car will crank but will not turn over. The car has been making a screeching sound when its starts for like the past couple of weeks. Its really loud and eventually goes away. Maybe this has something to do with my problem. This car has 198k on it but is in very nice condition. Always maintained. Any help?

 

You mean the car turns over but doesn't start.
A screeching sound would point to the drive belts and possibly to the water pump, power steering pump and alternator. The AC compressor could make a clunking sound.

I wouldn't make the EGR valve the prime suspect for rough idling.
I would first make sure the ignition is fine: spark plugs, wires, distributor cap and rotor.
2nd that there is no vacuum leak on the intake side: vacuum hoses, intake hose, brake booster hose, lower intake manifold gasket.
3rd that no vacuum line is obstructed, including the nipple for the EGR boost sensor at the back of the intake manifold.
4th that the MAF sensor is clean.
After all of that I would clean out the existing EGR valve, clean the throttle body and the EGR ports.
And finally I'd check the fuel supply system: pressure and volume, fuel injectors.