Why do Bosch type throttle bodies fail so often on Volvos? A theory..

[mrbrian200]

After watching this video and also noting that on my sister's old VW Jetta with a virtually identical style Bosch throttle body the internal gears still looked brand new at 180,000 miles whereas these gears wore/failed on my S60 at less than half that mileage..
[youtube][/youtube]

It occurred to me, when I inspected the TB on the Jetta, it was dry with NO sign engine oil contaminating the internals of the TB. On the Volvo, just as shown in this youtube video, there was engine oil contaminating the internals, though not as much on my car as there is in that video, there was a 'slick coat' of engine oil inside there.

So can we safely deduce that these nylon gears are not adequately resistant to oil/oil additives? I say probably.

What's the difference? Why did the inside of the TB on the VW stay clean but not on the Volvo? Ahhh.... TURBO!

On a turbo vehicle positive pressure will push PCV gasses (and oil) introduced upstream of the TB past the throttle plate and into the mechanism. The rubber seal around the plastic cover might be inadequate in that it doesn't provide a true seal against pressure (or vacuum). A NA vehicle would never experience this positive pressure condition, and thus, if that rubber cover isn't perfectly sealed, it would suck fresh air in through the mechanism toward the intake stream instead the other direction.

So, I propose, lacking an o-ring or some sort of oil seal between the butterfly and the internal mechanism, and/or these nylon plastic gears be made out of something else that is immune to engine oil/additives, these Bosch TBs as designed are unsuitable for Turbo vehicles. At least for long term use/expecting it to last the lifetime of the vehicle.

Edit: this seemingly experienced, likely professional mechanic states near the beginning 'these fail more often on Volvos for some reason'. Well yeah...Volvo makes lots of turbo cars, and has for a long time. I don't consider this so much a fault of Volvo, but a Bosch engineering failure to consider/address positive charge pressure in their design (that they sell to Volvo). With turbo and supercharged engines becoming more of the norm, the issue will become more widespread, at least on makes that use Bosch TBs.

[93Regina]

Good video presentation...

Cruise Dropout - I wonder if a worn gear(s) trips this issue...

[mrbrian200]

I didn't make the video. Came across it looking for something else. That's exactly what failed on mine.

[abscate]

That means we should see different statistics on turbo vs NA throttle body failures , if true.

We could just add an internal TB cleaning to the turbo pm list, too?

[wizechatmgr]

I wonder if the nylon parts could be replaced with Delrin and a silicone o-ring... Nylon absorbs moisture and as a result expands and shrinks just a little bit as the humidity changes.

[mrbrian200]

Those gears might already be probably are Delrin. Some grades mistaken for Nylon at a glance, my bad.

http://www.emcoplastics.com/assets/pdf/ ... Dupont.pdf

Delrin is resistant to a lot of chemicals, but not all. I would imagine anything listed as 'D-severe effect' and 'C-fair' would be detrimental after a short concentrated exposure (some spray cleaners?) or long term trace exposure.

https://www.calpaclab.com/acetal-polyox ... ity-chart/

Chemicals listed as 'B-good' might still have a long term wear effect (petro oil is listed as such). Heat might be a factor as well. There are quite a few substances Delrin really doesn't like. Including, keytones, lacquers, chlorine, certain oils, and ..umm.. fruit juice???

[June]

That means we should see different statistics on turbo vs NA throttle body failures , if true.

We could just add an internal TB cleaning to the turbo pm list, too?

Is there a thread to show the statistics age/miles/na or turbo of when these fail? Sometimes I wonder when the dreaded thing is going to fail leaving me stuck somewhere inconvenient. So far so good for my car. June

[mrbrian200]

You're likely to see fuel trim/MAF codes (but still runs and drives fine) before it gets to the point where you'd get stranded. That was my experience. I was getting intermittent fuel trim/MAF DTCs and an occasional rough start (when cold). But ran and drove fine except that engine power output didn't feel linear to the accelerator pedal travel below about 30% throttle. The amount of wear shown on that TB in the video I linked was way worse than mine. The car that came off of probably had intermittent CELs for a year or more the owner didn't get resolved until it finally got bad enough to trigger limp mode.

[callahanoffroad]

Those gears might already be probably are Delrin. Some grades mistaken for Nylon at a glance, my bad.

http://www.emcoplastics.com/assets/pdf/ ... Dupont.pdf

Delrin is resistant to a lot of chemicals, but not all. I would imagine anything listed as 'D-severe effect' and 'C-fair' would be detrimental after a short concentrated exposure (some spray cleaners?) or long term trace exposure.

https://www.calpaclab.com/acetal-polyox ... ity-chart/

Chemicals listed as 'B-good' might still have a long term wear effect (petro oil is listed as such). Heat might be a factor as well. There are quite a few substances Delrin really doesn't like. Including, keytones, lacquers, chlorine, certain oils, and ..umm.. fruit juice???

Some fruit juices are corrosive, like orange, lime, lemon and pineapple. Pineapple contains a chemical that is actually fantastic at breaking down animal proteins. Citrus juices contain citric acid, which also breaks down proteins.

I'm sure the sugars aren't great for the delrin's low-carb diet

[mrbrian200]

Looks like I got another one. Not my car, a friend of a friend's 2006 V70 (T2 LPT), I was called because they were having trouble figuring it out.
AF codes and high idle (among other unrelated DTCs). It was idling at 900-1000 RPM. It would initially 'try' to idle lower (roughly) but then RPM raised as it richened the mix to attain proper AF based on closed loop.

Capture.JPG (54.59 KiB) Viewed 2943 times

AT KPII/engine off the throttle plate position was sitting at 14.5%. Mine liked to stick at multiples of ~7% when the internal gears are worn/binding/sticking. This is probably evidence that leans toward a conclusion it's probably how they all act. I left this afternoon thinking he had an intake leak that I couldn't find and recommended arranging for a smoke test, that the 14% might be the ECU opening the throttle plate in preparation for start. Then this evening reexamined my head and checked how the throttle plate acts on mine. No, the ECU does not open the throttle plate at KPII. It sat at 2% on mine unless I pressed down on the pedal.

The interesting bit is that he replaced the TB for a bad position sensor about 6 months ago. Which is why I was wanting to discount the TB as a culprit. He bought the car within the last year. He paid ~$270 for the replacement TB, didn't remember where he ordered it off hand: likely not a Bosch TB, certainly not blue box.
So the 'cheaper' aftermarket TBs don't even last a full year! ..probably my whole point to this post. You just had to wait for it.

Footnote- large evap leak was the hose from the canister didn't get seated/locked into the purge valve fully and came out. And I switched out CP#3 with one of my spares. I made him aware that he needs an alternator rebuild. And lectured him regarding an unknown timing belt at 180k miles. And it's due for a WP soon.

Edit: how bad does this have to get before it triggers ECM-925/926/9270/9280 (throttle angle desired value does not correspond to the throttle angle actual value)? See frame data below to the right. On my car with a good TB, watching live try as I might (pressing the pedal at different positions/velocities) I can't get these two numbers to differ more than ~1%.