Have 1998 Astro 4.3 with 195k miles that set P0101, MAF A circuit range, P0404 EGR performance, and P0420 catalyst system efficiency below threshold, Bank 1.
Original owner, original cat converter and EGR valve. I was going to try cleaning everything...MAF sensor, EGR valve, and find something to clean cat converter. Is there a fuel additive for this?
Van runs good. Could cat converter be clogged beyond cleaning? Is there a test for a clogged converter?

 

"Is there a test for a clogged converter?"
If engine runs well( breathes well) then cat not interfering.
Regarding cleaning cat to increase its efficiency, could try cat clean fuel additive.

 

i investigated cat converter cleaners and I don't find many happy purchasers of cleaners based on reviews on Amazon. The reviews are full of people whose codes came back after less than 200 miles. I see the trick where the downstream O2 sensor is spaced back from the exhaust pipe, but this doesn't seem to always work based on reviews. Can the O2 sensor be dirty? How hard is an O2 sensor to remove? The van has been through 20 winters in the rust belt.

 

Chances are the cat has lost its efficiency over the past 20 years thus the P0420.
Soak the O2 sensor threads good for a day or two with penetrating oil if trying to remove sensor.

Were you able to fix the MAF/EGR codes?
Maybe do those first.
Can you post MAF g/s at idle and at 80% engine load?

 

Thanks for the help. My son is using the van so I only get to see it about once a month. I will do the cleaning, clear the codes, and then get the g/s data next time he brings it by. I don't live near any hills. How is 80% load typically achieved?