Hi, my experience may be of some help to you. My 99 Astro suffered the exact symptoms, fine at idle, fine at slow speeds, but push the pedal for anything demanding more jam and all you get is noise, some pinging, weird delayed tranny shifts, but no acceleration to speak of. Here is what I did to rectify the problem, and yes, all steps are relatively easy for anyone who knows the basics. :banana:
You engine light may or may not be coming on, I found that by finally driving the youhoo out of the van trying the old Italian tune up finally resulted in a check engine light, but if you are just farting around town, you may not get a light. Because a code scan costs a minimum of $50 in my town and I could buy a good OBDII code reader on sale for $69.99, that was a no brainer. Don't just jump to the conclusion that the Mass Airflow sensor is shot, as it tends to affect all RPM and power ranges, not just high demand.
Scanned engine which resulted in three codes 0101, 0300, 0420, manual says all point towards, Mass airflow sensor, engine misfire, and catalytic converter no operating properly. Now one can start replacing a Mass airflow sensor for $300 or take a step back and try a more sensible approach.
1. Look at all connections for loose leads,wires,connections
2. Change the Plugs,wires, cap and rotor if you do not know the last time they were changed or were changed more than 50,000 miles ago. Even if not the cause, now you have a fresh ignition.(~$100.00)
3. Replace the air filter and clean the entire breather box assembly (~$15.00)
4. While you have the breather box out, carefully clean the Mass Airflow Sensor with electrical contact cleaner], NOT CARB CLEANER (~$7.00)
5. Start it up and go for a run, see if it runs properly.
IF NOT
6. While running, tap the Mass Airflow Sensor with a screwdriver handle. If the engine stumbles and then recovers, then YES, The MAF is the culprit, or part of the problem. Replace and take for a drive to see if it runs properly.
IF NOT
7. If your engine didn't stumble with the tap test, there is only one thing left. An exhaust restriction that is probably a plugged/melted Catalytic converter. Have an honest exhaust shop cut it out and replace it with a section of pipe.(~$100.00)
For me, I made it all the way to step 7, My MAF was OK via the tap test and the CAT was melted to allow only about 20% of the exhaust flow.
My old stump puller is back, with more power than it ever had and I have a major engine tune up as a bonus. :layrubber:
Hope this works for you, don't worry, the system is not as complicated as some will lead you to believe, and 90% of power loss issues are related to one of more of the fixes mentioned above.
PS. cutting out the CAT did not cause any Engine Light Issues, my dash is beautifully dark!!
Good luck and happy trails!!