I installed a new cat, not a high flow one or anything but my other one was all broken and turned sideways inside so it was very clogged. My question is should my idle have dropped from about 1000-900 to 650, just wondering if that is normal?

 

my idle dropped a little too, not as much as yours though. are u sure when it was idling around 1.1k that it wasnt in closed loop, like starting it cold in the morning? but yeah a small drop in idle is normal if the exhaust flows more freely.

 

I just replaced my previous owner junk CC with my used AC Delco convertor I got with the 50K 3.4 motor that went into my Blazer.
I also read this thread before I installed it.
Was curious about results
My idle only became smoother.
YET MY TOP END HIGH SPEED POWER SURE DID COME BACK!
Currently no tach installed.
Before I installed this used convertor, let me explain.
It's a 1995 issued design, from AC Delco.
INSIDE LOOKED BRAND NEW
I held up to sun & looked thru it.
Only saw sunshine!
Makes me feel good about that 3.4 motor in Blazer.
I can tell ya the current AC Delco CCs are extremly high flow, unlike their previous efforts!
This convertor fit exactly perfectly, no true effort for adapting, all bolts lined up perfectly.
IF you have a chance to score one, try it.
Yes, I did get lucky, but I also obtained a low milage 3.4 motor. I'll bet one from a 3.8/V-8 powered 4th gen would work just as well!
Current (mine is issued in 1995) GM/AC Delco CCs are meant to last a very very long time.

The aftermarket convertor that fell to cement ground?
Clunk/rattle, stuff fell out!
Now to find one to create a better "Y" pipe from the "Y" pipe that came with that 3.4 motor. Those 3.4 "Y" pipes are larger.
I feel no true gain would/could occur going from a 2 1/4" "I" pipe to a 2 1/2" if the front "Y" is still choked up! I have a 2 1/2" muffler w/twin exit pipes out back.

 

anybody else have any problem like mine?

 

I recently replaced the rotted out I-pipe, muffler, and tailpipe on my 83 and noticed a decrease in idle as well. Now she idles around where she should (750).

 

me 2 ..i went from no cat... to a catco high flow...
my rpms went down by a lot...esp in idle

i did these

1. reset the computer (remove the battery)
2. my K&N was way too dirty...w/o the cat i dont
think this was a problem...
3. i readjusted idle and TPS sensor...a bit

now the car idles ok..im still not happy though
i think the TPS keeps changing values in idle...