Purchased this car with 154000 miles on it. Ran awesome for the 1st 400 miles. Now...... it has ZERO power when I attempt to accelerate. Weather I'm going 20mph or 50 mph. Also I will add "if" I can get it up to 50mph. I have had the following engine codes & I have had them cleared after replacing the part that was to fix the issue. Codes- P0300, P0132, P0138, P0117, P0108. I am not sure what to even attempt to fix next since now the check engine light is no longer on nor flashing. It seems to shudder when I attempt to give any acceleration. And I'm not why but it seems to idle fine & start fine. The engine revs normal if it is in Park or reverse. ANY input would be greatly appreciated. :-)

 

Sounds like a clogged catalytic converter. Were the O2 sensors, MAP sensor and ECT replaced and misfire corrected. Misfires can cause the cat to clog prematurely.

Check out these videos:
1. https://www.youtube.com/watch?v=Tj5NX1Ipfag

2. https://www.youtube.com/watch?v=TxP8SOpOG7Y

 

Those 3 senors were replaced & the light was cleared on the dash. However it made zero difference n how it runs. I held my hand over exhust & it has plenty of flow. It did not appear cloged.

 

It doesn't have to be completely clogged, just restricted.

 

The only code now that will come on if I attempt to drive it normal is P0300 and that is multiple misfire detected, etc: and it will go off after flashing.

 

P300 could be a few different things (plugs, plug wires, coil pack(s)), but I would bet money that it's the Cat. It will also set code P300.

Check out this video: https://www.youtube.com/watch?v=_92Y8bvO_ww

 

I had a friend with this problem on a 4.3 Vortec and it was a dirty MAF sensor. I hope you figure it out.