I have 2000 Astro 4.3 with random misfire P0300 you only notice any issue when trying to maintain highway speed and then you feel the misfire let out of the fuel, add slight fuel, or pulling up a hill and it goes away. three shops have scoped it only consistent signs is random misfire on 6 of 5 cylinders. Occasionally it will throw a P0102 Mass or Volume Air Flow Circuit Low Input however it scopes out fine. The cam retard is @ -12 and only varies by 2. I have tried three used distributors from a friends garage and they showed the same. The misfire shows up worse on humid or rainy days. The distributor cap does collect green corrosion constantly. i have changed fuel pump, filter, cap and bug, wires, plugs, cat, cleaned the maf! Any idea?

 

Sounds like your injectors are gumming up. Get a bottle of GM Fuel System Treatment Plus. This is special formula fuel injector cleaner and what GM suggests using in a TSB to clear up cylinder misfires. I've had to use it on my last three vans and it did a good job clearing things up.

Clean your Mass Airflow Sensor.

Some reason the ACDelco/Dephi caps and rotors seem to work best in these vans.

 

<TABLE border=0 width="100%" itxtNodeId="1" itxtHarvested="0"><TBODY itxtNodeId="2" itxtHarvested="0"><TR itxtNodeId="4" itxtHarvested="0"><TD vAlign=top width="100%" itxtNodeId="5" itxtHarvested="0">I have 2000 Astro 4.3 with random misfire P0300 you only notice any issue when trying to maintain highway speed and then you feel the misfire let out of the fuel, add slight fuel, or pulling up a hill and it goes away. three shops have scoped it only consistent signs is random misfire on 6 of 5 cylinders. Occasionally it will throw a P0102 Mass or Volume Air Flow Circuit Low Input however it scopes out fine. The cam retard is @ -12 and only varies by 2. I have tried three used distributors from a friends garage and they showed the same. The misfire shows up worse on humid or rainy days. The distributor cap does collect green corrosion constantly. i have changed fuel pump, filter, cap and bug, wires, plugs, cat, cleaned the maf! Any idea? </TD></TR></TBODY></TABLE><TABLE border=0 width="100%" itxtNodeId="1" itxtHarvested="0"><TBODY itxtNodeId="2" itxtHarvested="0"><TR itxtNodeId="4" itxtHarvested="0"><TD vAlign=top width="100%" itxtNodeId="5" itxtHarvested="0"></TD></TR></TBODY></TABLE>I was wondering if you may have found a answer to your p0300, I have a 1997 with the same issues, I get the p0300, and the one for the cold air. I have replaced wires, cap, rotor, coil, dist, fuel injectors. My van only has 67,000 miles. when it is damp out its a rough ride, when its dry out it only does it on the highway at a steady speed! i have been chasing this issue for 2 years now

 

Man, I was just trolling around looking for a solution on moving a 87 camero rearend to my astro van and I found this.

I had the exact same problem with my 4.3 I also pulled my hair out and replaced a bunch of crap.

The problem is!!!!!!

The distributer gear! Thats right! The stupid gear and the end of the shaft gets worn and there is too much play. Your timing starts to jump around and the sensors and computer can't handle it. You will feel a little intermittent jerk at highway speeds and it will drive you crazy occasionaly throwing out codes you listed!

Enjoy!

Randall