I have a 2004 chevy express 1500 cargo van, 4.3 v6, rwd. About a week ago I was driving and the check engine light came on, Once I came closer to a small hill it started flashing and the van would barely go no matter how much gas I gave it, then just take off, then again barely go. I had to make it home so I made it to the freeway and on the freeway it worked great ran smooth but when I slowed down at the stop light it would idle like it was about to die. I constantly had to put it in nuetral and give it gas. Next day I had to go to work so I started it up in the morning and it ran great untill it warmed up then it started to do the same thing. After work I took it to a shop to have the code ran. They said random cylinder misfire and o2 sensors. I took it home and changed the spark plugs, wires, distributor cap, rotor, ignition coil, fuel filter, all 4 o2 sensors, and added a fuel injector cleaner to the gas. Now the only code is PO300 but it seems to run even worse even on a cold morning start it just shakes and check engine light flashes and it struggles to go. Ive put all this money and time in please somebody help me figure this out.

 

Also I should add it starts great, instantly, and idles good now but still runs horrible when pressing gas

 

I worked on a co-workers silverado 1500.
And they explained the same problems to a tee that you described.
so I started to drive it myself to see first hand. just as they said
so I got back to the shop and started checking things and found out that
who ever did the last tune up crossed the 3 and 5 spark plug wires so changed them back to their correct location and took for a drive and that fixed their problem. not saying that that's your problem but wouldn't hurt to double check the wires.

 

As embarrassing as it is to say one of my plug wires was not snug enough, after properly installing it it works great and check engine light is gone. Unfortunatly all the driving I did with it in this condition has taken it toll( work van no choice) I am not only out the $ for the new o2 sensors but I think I need a new cat. The other night I came home and peeked under and saw the drivers side cat was glowing red, I can also feel a loss of power when climbing hills. Final straw was the tiny shiny metal shavings I'm seeing coming out of my muffler :-/

 

Great now I have a PO135 and Po161 code help anyone?

 

P0135: O2 Sensor Heater Circuit Malfunction(Bank 1 Sensor 1)

P0161: same thing (Bank 2 Sensor 2)

Restriction in your exhaust system?

 

Guess I just needed to clear the old codes. Drove it all day, I think im finally good.

 

I have the 4.3L V-6 in my Express too. Be advised, there is a known issue that the gear on the distributor wears and contributes to all of your problems.

Prior to replacing the distributor ($92 at Autozone) I had to replace the MAF, EGR and the Cat. Had I taken care of that gear in the first place I wouldn't have had to replace the cat for sure.

She runs like new now, and the mileage went from 10 mpg to 16 mpg driving with traffic on the Interstate (I have the 4:10 differential). I hesitate to state what speed that is, just flowing with traffic! : )

 

It definitely is either tune-up issue or engine coolant.

 

I have the same issues... Cat exploded, and was replaced as well as the muffler. Still a random misfire. I'll pass on the info from USA 1 above, to my hubs. Thanks for the info. My van doesn't even have 90,000 on it yet.