Hazard15301

iTrader: (5)

Ok, let me tell the story to lead up to my question.

Ever since I had the car, it had a bad exhaust leak. I drove it like that up until the inspection ran out. It had a straight pipe all the way back to the mufflers, no cat. I had to cut a section of pipe out and put in a cat I had laying around, just to pass emissions. I intended it to be a temporary thing, so I just welded some pipe slightly larger than my exhaust onto the cat, and clamped it on. I ended up never replacing the pipe section, just left the cat on. After my rebuild (beginning of this year), and changing the motor mounts, it seems the exhaust manifold side of the engine moved slightly forward, which made the exhaust fit differently. Every once in a while since then, when I hit a bump or scraped the ground, the exhaust would separate. After a while I got tired of reclamping it over and over so i just welded the cat directly onto the pipe. I also replaced the exhaust gasket too. This made a world of difference in the car. It accelerates better, and much quieter. But ever since that fix, my idle has started sucking...

It's totally random, doesn't make sense to me. Doesn't matter whether the car is hot or cold, starting up or driving for an hour. It will idle at around 500 for a second then die. Other times it idles right at 750-850. To top it off, my emissions expires at the end of the month. In preparation, I'm changing all my vacuum lines. I think my EGR valve is bad, because it doesn't hold vacuum. So theres a potential vacuum leak right there. But I guess the question is what could have changed to totally affect my idle? I'm going to tear into the motor today and do the lines. So.... to summarize that long "interesting" story, my questions are:

1.) Why would fixing the exhaust affect my idle?
a.)What to check... What to replace, etc

2.)Will blocking the EGR have any detrimental effect on the emissions test, or driveability?

Thanks!