Have you checked the ignition coil yet? Probably would inspect the cap,rotor and ignition wires also.

 

Replaced the coil. Did spark plugs, distributor etc but that was a few years back. I did inspect the distributor pretty well a few days ago. All seems right there.

 

If it's been a few years since a distributor cap and rotor replacement that would be a good starting point to do and rule out... get the better one, the cap with brass contacts n rotor (cost around $20. cheap fix if that is it.. happened to me on my 99 cargo not too terribly long ago (1-2 years) , was having misfire codes on #6 and #8 cylinders too. I ruled them out thinking I had replaced them just around 20-25k miles ago n they really didn't look all that shabby as others I had seen and ran well. Check and lightly clean the pick up coil sensor contact while the rotor is off too while apart. I've got 30k easily on this new set since replacing, no problems yet. have been using higher octane fuel too since then, has helped a bunch quieting the high rpm valve flutter when traveling up a grade and give it some help on the pedal.
Wondering also, did you clean out the iac orifice where it mounts to the throttle body too? Maybe the throttle body could use a good cleaning too, disconnect neg battery and use some electrical spray cleaner on the electrical connection plugs as well
Just some stuff to consider n try, good luck

Oh was going to mention, if your new 02 sensor is bosch take back and see if you can't get a Denso brand

 

Could the throttle body gasket be bad?

 

I am definitely going to look again at the plugs and the cap and rotor. A fairly simple job that could make a difference.
Also getting a vacuum gauge to try to see theres a problem there. '
I did clean out the iac orifice, and looked down inside the throttle body and it looks really clean in there.

NOW I have replaced the upstream 02 sensor (not a Bosch but also not a denso) and the van ran great for two test drives. Day 1 about a 5 mile trip around the neighborhood stopping and going, A/C going and not going, idling and pretty much trying everything, but it never dies once.
Day 2 about 10 miles no issues, then all of a sudden disaster. It's bucking and surging and hesitating and backfiring now, but only when in gear and trying to accelerate. If I pop it out of gear and rev the engine and drop it back to idle it sounds perfect. Put it back in gear and the bucking etc is back.

OMG I hope it's not the CAT, I really don't want to have to go to that expense

Any ideas? Seems we keep fixing one problem only to have another one pop up.

 

Maybe, haven't gotten to that point yet, was hoping not to have to take the throttle body off..... but now there are new symptoms, check my reply to JFloors above.

 

Just coming back here to add today test drives to the mix.
As I said yesterday, after replacing the 02 sensor, several good test drives with no symptoms at all, then new symptoms: It's bucking and surging and hesitating and backfiring at manifold now, but only when in gear and trying to accelerate. If I pop it out of gear and rev the engine and drop it back to idle it sounds perfect. Put it back in gear and the bucking etc is back.
Todays test drive it was fine until the engine started to warm up, then shuddering and surging and bad hesitation while in gear and driving. We stopped in a parking lot and removed the 02 sensor (the upstream one that we had replaced), thereby creating a small gap to vent the exhaust, ran it around quite a while and it ran perfectly (other than the loud engine noise.) This was the first time through the whole saga that we got a check engine light. We do have a blue driver scan tool, we've had a problem getting the app to work on either of our phones, but today I tried the app on my tablet and it connected and verified that the code is for oxygen sensor (duh, it was removed so yea, nice to know that throws a code.)

So does this mean the cat is plugged?

We still have a few other things to do, waiting on a vacuum gauge to get here, thinking that will maybe give us some more info. I have read we should use the infrared thermometer on the cat to see how hot it's getting (it seems REALLY hot at the back even without checking it).
And we took off the distributor cap again and inspected all around in there, the ignition pickup had no visible problem. (may replace it anyway at some point, it has never been replaced.)
Hubby pulled the plugs to inspect them, seemed ok, but presumably we will pop in a new set of plugs just to have that ruled out as a possible problem.

Frankly we are hoping not to have to replace the cat. Hubby can weld but welding the converter onto existing pipes may not be that easy so we might have to opt for the whole converter assembly, more than double the price. Ugh.
Have any of you ever welded a cat on?

And by the way, should these new symptoms justify starting a new post with just those symptoms in the title?

 

Just keep this one going. It let's people refer to past conversations in the thread to find little tidbits of information. By removing the sensor and opening up the exhaust, it sure sounds like a plugged exhaust. A vacuum gauge will tell you for sure. A lot of catalytic converters are bolt on. Exhaust work is one of those things I can do but there's a shop that does good work at reasonable prices and a LOT faster than I can do it laying in the driveway. While it may be your converter, it could also be your muffler. If you just drive around town and don't get it really hot on long drives, it can rust inside and collapse. You might even have a mouse nest in there. I've seen whole mouse hotels in exhaust systems. Complete with a little mouse in a uniform. (A door mouse. ) Don't rush to condemn an expensive part when it might be a cheaper one.

 

Yep, removing the front O2 sensor as a diagnosis is correct in your situation. The result that you have of running perfect means you cat IS bad.

You can use any cat you want to. Any independent muffler shop can put any cat on for about 50-100 bucks. You just need to find a shop that is willing to work with you.
When I had my V6, I had a shot cat too one day. I bought a generic 3.8 GM V6 cat which was about $85 and had a indy shop put it on for $80 bucks.

Welding isnt that hard, but you will need to figure out what kind you want to do and then either rent the welder of buy one...for that price, you might as well just find a shop that will help you. You can also take out the exhaust system, take it to them and have them do the job. In some states it is illegal to put on another brand or style of cat, but if you bring just the exhaust, they can do the job legally. It all depends on the state and area.

I had one like the one below in the link...it worked fine...cheers!

 

We went ahead and took off the muffler and tailpipe, neither one is restricted in any way. Nice and clean. Today we have a new vacuum gauge so will run those tests but it seems we are needing a CAT.