Waring a bit of a long post! (Sorry)

Hello all, my first post here I have a 1996 Trans Sport minivan (3400 V6), not a hit to a lot, but I like it and has become my project ride.

Let me get to the point, The van was fine before I had it detailed at a local dealership, ran perfect. When I picked up the van it was million degrees in the cabin, and the engine was up to temp. So I can only assume they left it idle for who knows how long with the heat on full blast "to dry it". Dealer told me pound sand when I said something is wrong with the van.

After that it it has picked up few quirks, the tach will bounce up and down like it is breathing maybe 75-100 RPM, It only seems to happen at a low idle like in drive or in park when it enters that low idle state. Under the hood you can hear the "breathing" the rymthic change in idle speed. Also when taking off from a traffic light it will buck/surge pretty minor but still noticeable.

My limited troubleshooting skills have lead me to replace the IAC and MAF along with the plugs and wires. Also the thermostat was replaced. Van has 93K, lower intake I am 90% is still good, it will hold pressure and no loss of coolant.

When I got the van I did fuel filter trans service air filter etc, been maybe 1000 miles ago. No check engine light. Someone suggest I change the FPR (fuel pressure reg) and it made no change in the problem

So what do you guys think the problem might be?

Here is a video of the issue:

You Tube

Try spraying can of carb cleaner around the top of the engine for a change in idle....

Sprayed carb cleaner on top of the engine no change also tried vac fittings etc. I also replace the PCV still no change.

Do you have access to a scan tool that can read O2 data?

Scanned for codes?

One other thing......you changed the IAC, but sometimes it can be the harness the IAC........

Yes I have a tech II and other tools, I did look at the data, but I am no expert at all. The post cat O2 was replaced when I got the van, the pre cat O2 seems to flip like it should the post cat 02 seems to stay steady. Is they correct for what they should do or am I missing something?

Front sensor is for fuel control and should swing from about .1 to .9 volts in a quick lean to rich pattern. The rear sensor is for monitoring the catalyst and it'* ability to store oxygen. That sensor will hang around .7 to .8 volts and will not normally swing low unless the PCM is running a test for the cat and it'll drive the fuel injectors lean and the extra oxygen should drive the rear sensor low within a specific period of time. If it takes to long to respond it will flag a catalyst deficiency.

I'm a little late to the game: How is it running now?

To me it looks like it was running fine until the interior was detailed and then ran badly. That strikes me as moisture getting into something that it shouldn't. Now that it has been almost two weeks, is it running any better?

Have you tried keeping the windows open on dry days to let any residual moisture out?

I have a friend who used to detail cars for a dealership, and your detail job (wet interior and using the heater to dry it) reminds me of how the place he worked would often drench the carpet in a solution of some sort until it had pooled about an inch deep, let it sit that way for an hour, then suck out what they could with a shop vac and then close up the interior with the heater on high to dry it. He said it worked wonders on some pretty bad carpet, but also probably rusted the floors out. My thought was always "what about the wiring under the carpet and all that humidity in the dash electronics?"

For the record, he didn't care for that practice, but the employer made them do that as standard procedure fairly often.

It may be a good idea to get some compressed air & blow out the wires leading into the IAC & Throttle position sensor.
Then also remove the wiring connector,and also inspect inside the connectors, for moisture.
Might as well clean the IAC and port while you are there as well.https://www.gmforum.com/normal-maint...800-v6-307092/