88 wolfsburg. Been Stumbling at various RPM levels

[Creativemind]

I just got my Rebuilt Engine back in my automatic 88 wolfsburg. It's
been Stumbling at various RPM levels between 2100-2300rpm & 3400- 4000 rpm's.

Now when I say stumble I mean it runs then it hits the rpm mark and it pauses for a second then continues to provide power.

It has good power through the band but if you are not pushing the
accelerator down and staying steady at any of the RPM ranges stated
above it will stumble once in a while, not continuously.

The engine only has 100 miles on it so far. Mostly country road
driving with very little highway driving.

It has a brand new bosch O2 sensor, all other sensors on the van are
new.

New Fuel Lines, Injectors are 2 yrs old. New fuel in the tank, all old
fuel in the tank was removed. All new fuel lines on the tank as well.
New Oil filter and Fuel Filter. Air Cleaner just cleaned.

Any ideas of what I should be looking for?

Could it be the advance timing on the engine?
Maybe it was set incorrectly?

AFM problem?

Thanks,
Robert
NY
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88 Wolfsburg, Automatic Silver Vanagon, 250,500 miles. Rebuilt Engine. 8/09

[tencentlife]

Maybe this will help, or at least it will rule it out:

http://www.thesamba.com/vw/forum/viewtopic.php?t=369815&highlight=afm+video
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Experience is kryptonite to doctrine.

[Creativemind]

Thanks TenCent for that info.

Since the AFM was working fine before the rebuild and it was just put back in the van without any adjusting maybe that is not it.

It has been suggested that since I rebuilt the engine maybe I should replace the plug wires & cap as well? I replaced them about 3 yrs ago.

Another thought was that the TPS would out of alignment and may need adjusting.

Any thoughts by anyone?
The van has all new sensors throughout the van.
All new vacuum lines.
All new spark plugs.
All new filters.

Engine timing was done my mechanic who may have not done it properly, he was suppose to do it via tencent's advance timing technique. Not sure in the event he did it incorrectly it would have this strange effect. TenCent any thoughts on that?
_________________
88 Wolfsburg, Automatic Silver Vanagon, 250,500 miles. Rebuilt Engine. 8/09

[tencentlife]

I don't understand why some people have trouble with setting the timing that way, it's so much simpler than the book procedure but gets you to basically the same place. The main error I see being made is that somehow people think it's an addenda to the book process, so they try to combine the techniques. Wrong. It is a replacement for the other way. Ignore the book, forget anything it says, and instead follow the method to the letter. Make sure your mechanic understands that, even though I think I've made that very clear in the places I've already described how to do it (which I know you've done a complete survey of already).

I don't know if off-timing might be the cause of your symptom. If it runs well and delivers good power then it can't be too far off, but if there's any doubt have it checked again since timing is one of those baseline things, like fuel pressure, that you have to get right before proceeding or looking for other causes.

I do think your AFM could still be a contributor. Never assume anything just because you think something works based on previous performance. The AFM in the video I shot was working fine, too, with the old tired 1.9 that was in that car, but with the new engine it's operating in new ranges and the owner was being driven nuts over the same symptoms as you describe. Just like you, he ruled out certain things because they worked OK before. Well, surprise! Things change.

I get a good laugh every time I see someone rule out a component as a potential cause of some mystery symptom just because it's new, for instance. They go round and round and waste days and days and lose sleep and finally do what should have been done right from the start, which is to verify operation, and guess what? a lot of new components are bad on the shelf. Some people want to blame the Chinese, thirty years ago it was the Mexicans, but that BS was as insufferably ignorant then as it is now, and all it shows is how green they are. There has always been a good percentage of bad stuff on the shelf; electrical has always been the worst with 25-35% of new parts being bad in the box. Buying OEM Bosch only increases your odds a few percent. Verify. Verify. It takes less time to test most things than it takes to ask some internet "guru" to know something he can't from where he sits, and which you should already have the data on before asking any questions. Do the AFM test. Then you'll know. Do the fuel pressure test. Then you'll know. Do the O2 signal output and coax grounding tests. Then you'll know. Test and verify operation of the TPS. Then you'll know. That's called due diligence.

This is a general rant and not aimed at you or your case, but I just want to stake out my position on this aspect of diagnosis: I don't know shit, from where I sit. Gather real facts and bring them to the table and then we can discuss them. Most of the time, if you gather the facts, you find the problem, and then if you still just have to type something you can tell your success story.
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https://intrepidoverland.com/vanistan/

Please don't PM here, I will not reply.

Experience is kryptonite to doctrine.

[Creativemind]

Strange thing, I was all ready to start testing everything as I was told to do by so many here. Check the vacuum lines, TPS, AFM, etc...

Then I decided to take it for a drive as it only has 120 miles on the engine. I drove on the local country roads for 30 minutes with no stumbling, I pushed it hard, then let up on and repeated this during my whole drive. Still No Stumbling.

After I did my errands I decided to take the highway and push it to 4500rpm, drop it down to 2000 and repeat as TenCentLife had suggested on breaking the engine in.

Well I did this for 30 minutes. I could not notice any stumbling. I even drove up a long steep incline on the highway for 10 minutes, not a problem. None that I noticed. Drove home and parked the van.

1 hr later I decided to go do some more errands. On the way back I was on the onramp for the highway and pushed it all the way, flooring it did something I have never experienced before.

I got a JOLT OF POWER like I had never seen before,... my automatic instantly became a stick! It went steadily to 3000 rpm then like a bolt of lightening hit it! It went to 4000-4500 rpm and Van shot off like a rocket.

Now when I use these terms and Vanagon together it seems ludicrous but honestly I have never experienced anything like it before. I kid you not! It was like letting the racehorse out the gate.

This all leads me to believe there may be an issue the TPS that it might be sticking? Or the throttle system itself may need lubrication or an adjustment of some sort?

What are your thoughts.

Thanks in advance.
Robert
_________________
88 Wolfsburg, Automatic Silver Vanagon, 250,500 miles. Rebuilt Engine. 8/09