Ok, we have a 2003 Chevy Blazer 4wd 4.3L Engine. Our cat was making a horrible racket and we ended up replacing it. After about 3 days the car started running horrible and now it has got to a point it barely goes over 10 mph. The only code we keep getting over and over is P0101, which is for MAF.

We have since replaced the MAF, MAP, TPS, air filter, replaced all spark plugs, fuel filter, fuel pump, new battery, new alternator, and PVC valve, not to mention fully cleaned the throttle body. The car will start and idle just fine but after it hits normal running temperature the idle gets a little rough and will not drive past 10-20 mph. If you rev the engine it will get to about 2500 rpms then bog down. After more work under the car we have found that the new Cat is rattling like crazy just from the smallest whack or revving up the engine. Is it possible when they put on the new Cat, they damaged the new one?

I have yet to do a pressure check in front and behind the Cat but I'm planning on that. The one thing I have noticed is that in front of the Cat and the Cat itself is really hot but for some reason after the Cat is almost cold.

 

Yes, it sounds like a cat problem. The new one could be defective, or the problem that caused the first one to fail (whatever that is) is still present. You can do a pressure test, but it's easier to drill a couple of big holes in the pipe right before the cat and see if the power comes back. Or, if it can be unbolted, do that. Obviously, that would be a test, not a permanent repair.

You can also put a vacuum gauge on it and hold it at a fast idle. If vacuum starts going down while holding at a steady speed, you have an exhaust restriction.

 

We're planning on going Mon. to rent a compression gauge and test before and after the Cat. At this point I'll be glad if it is Cat so we can replace it and get the car back. If it is the Cat I'm tempted to leave the O2 sensor before the Cat out so I can get it to the muffler shop.

 

There you go. I didn't even think of pulling the O2 sensor out.