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A year ago, my 96 GS passed an emmission test fine. Ive noticed that lately, its been BAD!

Im geting my exhaust re-bent and installed, so when i do that i will get a new Cat.
What else would help?

New O2 sensors.

Set the idle, the timing and the TPS and make sure that the intake is well sealed. Cleaning the throttle body is a good idea as well. General tune up stuff will ensure that your A/F mixture is as accurate as the stock ECM can make it.

run some seafoam threw the intake and do an oil change. itd be a good idea to make sure your egr is functioning properly before you go for the test.

to test the valve itself unplug the vacuum line that connects to the egr from the solenoid and suck on it, if you feel it raise and hold a vacuum then drop when you release the suction the valve is functioning properly., if your not getting any codes for the egr your solenoids are probably hooked up and functioning properly.

theres also this stuff called guaranteed to pass you can try. its like $15 and if you fail after fallowing its directions theyll give you double your money back.

I would start by doing a full diagnostic. Not with a handheld scanner, but with a scanner interface and a PC (it gives you lots of extra info). Then, based on what the scanner tells me, I'd start fixing things.