Chevrolet Repair: 91 S10 Blazer, no acceleration, bad idle, throttle position sensor, poor gas mileage

Question
Van, I have a 1991 S10 Blazer and about 2 weeks ago it just started running really bad, making allot of noise, ect. My Catalytic converter was original and had broken, so I replaced it. That helped a little. Still had poor acceleration and bad shaking. The coil wire was severely corroded at both ends so I replaced it, that helped tremendously, but it still is not right. The plug wires look good at both ends, plugs and wires are going on 3 years, I had a vacuum line collapsed, replaced it, replaced the coil, still have bad shaking and poor acceleration. Used a GM code reader and got nothing but 12's, indication the test was running.  Swapped out the black computer control card with another that I had, no difference. I am getting really poor gas mileage, and the temp is topping 210 and has never done this.  The engine is only 2 years old as of May '05 and has ran better than the original up until this time.
What am I missing.
Thanks

Answer
Hello Perry,
Sure could be a vacuum leak.
Low fuel pressure is also a possibility.
On the vacuum leak, check the EGR valve. If it seats on a piece of carbon, it will be like a huge vacuum leak.
I would connect a vacuum gauge.
Then I would connect a fuel pressure tester.
Brake booster is another possible cause of vacuum leak.

Throttle position sensor can cause poor performance also, since you are mechanically opening a throttle plate allowing massive amounts of air in, but no signal to the computer to add fuel. Check the TPS before just running out and buying one though.

Then there is always the oxygen sensors.

Generally speaking, though, if the sensors are the problem, the engine will run pretty fair when cold, but run terrible when it warms up and goes into closed loop, since the sensor values are not used when the engine is cold...it uses default values.
The vacuum would still affect it though.

Van