egr, what is it for?

Exhaust gas recirculator, and it does just that, it send exhaust gases back through the intake to reburn any unburnt fuel

exhaust gas recirculation, basically takes ur unburnt fuel in ur exhaust and puts it back into the intake

First check to make sure that you have vacuum going to it, then check to see if the egr holds vacuum through the port that the vac line was hooked to. If it holds vac. then the diapham is good

do you actually need it??? how would the car run without it or with a bad one

How about if you have an offroad h-pipe... how would it take tha unburnt gas out?

ttt, i want to now also if you can run without it and if its needed for smog in california.

the EGR is used at part throttle (Cruise). as said, the EGR introduces spent gasses into the chambers (at cruise) to help cool the chambers, reduce emissions and raise fuel economy. the computer sends the signal to the solenoid to let it know when to allow vac and activate the valve.

i dont see a point to removing the EGR - it helps when you dont need performance, and is inoperative when you do want performance. do note that the spent gasses are quite diluted - they dont burn well in and of themselves. the puter knows this and when the EGR is flowing, the puter adds a ton of timing (knowing the mixture is diluted). if one removes the EGR plumbing w/o letting the puter know (burn a chip, etc), one can see pinging issues as a result.

if you apply vac to the line on the egr while idling (when EGR does not normally flow), if the idle degrades considerably, that suggests the valve is working.

there are several other tests, which are more involved, if someone needs troubleshooting.

if more info is desired, i know Michael has some nice write ups on it (not poorly written like mine), as do JR and some others.