94 s10 rough idle

94 s10 blazer 4.3 cpi
It's still beeen cold around here but details are:
Starts up great cold. after warming up and driving for awhile when at a stoplight it shows the oil pressure dropping to about 10 on the dash
and it idles rough(if i put it in nuetral it's not as bad). runs fine otherwise.This problem started off slight and has since become more noticeable.Howevre as soon as you barely touch the gas it goes up. When driving the pressure goes up to 40 or slightly above(where it's always been).The car drives fine when moving If you turn off the car it will start great again for the next ten minutes after that it takes a bit to get it started. If i give it a little gas it starts quicker. Also this winter it seemed the alt upon starting was at like 16 volts and then after awhile it comes down I had the sulpher smell sligtly last summer and earlier this year. Oxygen sens is original.cts replaced this summer. Another thing i noticed is that running the car for three minutes i can't touch the pipe before the cat but after the cat the pipe is still almost/is touchable. I've smacked the cat but don't really hear it rattle.LAst emission check my hc's and co was up.127 for the hc at idle and .10 for co % at idle. Numbers dropped significantly at 2500 rpms
I'm thinking 1. bad cat since the problem has gotten slowly but progressively worse 2. stuck egr 3.CPI is leaking have to go buy a 30 torx and peek inside
Oh I'm not noticeing any real heavy duty gas smell from the engine bay after running or starting up. If i rev the engine there's a stumble when it comes back down.No codes set.I did find the vacuum tube from the air filter to the engine was off/put back on but no difference
Sorry about the length but try to be accurate. Any ideas?
Thanks Mike
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anyone?? ideas.
How about if the cat was definately bad would i smell more richness out of the exhaust upon startup? I bought a vacuum gauge so i'm gonna check vacuum as soon as i have a chance. And I never get black smoke upon startup
thanks
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Well, here's a little more info. I used an IR thermometer to check the temp along the exhaust. I got 380 right before the cat ,about 600 degrees right after the cat , 350 right before the muffler and 250 right after the muffler. I just started to hear a rattling or something in the muffler. Perhaps the cat is disintegrating and a piece went into the muffler and is clogging slightly? i also checked vacuum at the manifold and it was showing about 18 at idle when i would start to rev it up it would drop low then go up to about 20 -22. when i let go off the trottle it would drop way down low then recover.
Ideas?
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