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Throttle body cleaning and a few related questions.

E28 technical advice asked and given! Troubleshooting, modifications and more.
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Freight
Posts: 95
Joined: Dec 26, 2024 3:19 PM
Location: NY

Throttle body cleaning and a few related questions.

Post by Freight »

I pulled my throttle body to clean it up and adjust the TPS and plate. I found the entire throttle body coated with oil - not dripping, but coated. It doesn’t drip back past the breather/valve cover breather, so it must be just vapor and it may be the first time in 162,755 miles that it’s ever been removed and cleaned. Car does not consume oil at all. No smoking from the exhaust;
1) Is this a problem?
2) Do I need a catch can? 

I didn’t realize there was a gasket. It appears in good shape so I reused it.
3) Not a problem, I assume?

Throttle plate, after cleaning, rests with just a cunt hair of light visible around it. Filled up with carb cleaner on either side and it’s essentially water tight but for a very very slow drip down past the plate. I adjusted the tps to trigger at the slightest throttle input. Basically as soon as the backlash in the spring is taken up and the plate begins to move, it triggers. However; it triggers as WOT when the throttle is about 3:4 open.
4) Is this normal?

The plate doesn’t touch the body when closed, though naturally it is slightly worn finish where they meet at idle, not surprised….but on one side, at one corner the plate makes the slightest contact where the rod(?) enters the the TB!. This is due to the plate being the absolute tiniest bit off center. Shifting the plate over like .02mm would resolve it.
5) leave it alone, or should/can I shift it over next time I pull the TB?

Lastly, at WOT, the plate goes beyond fully open, by a few degrees. Enough that it’s visibly past perfectly parallel to the airflow. To be clear, it opens too far, beyond 90*, rather than being unable to open far enough. 
6) how do I correct this? Tighten up the throttle cable? Adjust the pedal stop? 
turbodan
Posts: 9366
Joined: Jan 09, 2007 10:19 PM

Re: Throttle body cleaning and a few related questions.

Post by turbodan »

The throttle body is just downstream from the crankcase breather, which connects between the throttle body and AFM.  It is completely normal for there to be some deposits here.  Catch cans are silly, I don't even run one on my turbo car.  Oil consumption is the primary indicator of engine health, and if it's not using oil and smoking we can confirm that it's not blowing engine oil into the intake.

What comes through the breather is a mixture of water vapors and volatile hydrocarbons.  These often condense and deposit in the throttle body but are not likely to accumulate to a problematic extent.  The system is intended to scavenge undesirable vapors and maintain a slight vacuum in the crankcase.  It's a very good design with no moving parts and unless the rings are tired it does a very good job of managing the normal volume of gases produced by blowby.
Freight
Posts: 95
Joined: Dec 26, 2024 3:19 PM
Location: NY

Re: Throttle body cleaning and a few related questions.

Post by Freight »

turbodan wrote: Apr 23, 2025 11:12 AM The throttle body is just downstream from the crankcase breather, which connects between the throttle body and AFM.  It is completely normal for there to be some deposits here.  Catch cans are silly, I don't even run one on my turbo car.  Oil consumption is the primary indicator of engine health, and if it's not using oil and smoking we can confirm that it's not blowing engine oil into the intake.

What comes through the breather is a mixture of water vapors and volatile hydrocarbons.  These often condense and deposit in the throttle body but are not likely to accumulate to a problematic extent.  The system is intended to scavenge undesirable vapors and maintain a slight vacuum in the crankcase.  It's a very good design with no moving parts and unless the rings are tired it does a very good job of managing the normal volume of gases produced by blowby.
That’s what a figured. There’s always gonna be vapor in the crank case, and it’s gonna coat the intake, but I’ll admit this is the first time I’ve ever had a throttle body off an engine so I wasn’t entirely sure what to expect. It was truly just a misty coat, and like I said not enough to pool and run back down the intake past the breather.

thanks for easing my nerves 😬 
Aldo525
Posts: 459
Joined: Mar 24, 2021 3:04 PM
Location: Puerto Varas, CHILE

Re: Throttle body cleaning and a few related questions.

Post by Aldo525 »

Freight wrote: Apr 23, 2025 2:07 PM
turbodan wrote: Apr 23, 2025 11:12 AM The throttle body is just downstream from the crankcase breather, which connects between the throttle body and AFM.  It is completely normal for there to be some deposits here.  Catch cans are silly, I don't even run one on my turbo car.  Oil consumption is the primary indicator of engine health, and if it's not using oil and smoking we can confirm that it's not blowing engine oil into the intake.

What comes through the breather is a mixture of water vapors and volatile hydrocarbons.  These often condense and deposit in the throttle body but are not likely to accumulate to a problematic extent.  The system is intended to scavenge undesirable vapors and maintain a slight vacuum in the crankcase.  It's a very good design with no moving parts and unless the rings are tired it does a very good job of managing the normal volume of gases produced by blowby.
That’s what a figured. There’s always gonna be vapor in the crank case, and it’s gonna coat the intake, but I’ll admit this is the first time I’ve ever had a throttle body off an engine so I wasn’t entirely sure what to expect. It was truly just a misty coat, and like I said not enough to pool and run back down the intake past the breather.

thanks for easing my nerves 😬 
My comments:

3) Gasket is very cheap, so it's better to replace with a new one to avoid vacuum leaks.
4) Normal, it's the way that TPS works, but the "trigger" you mention is the "beep" of a multimeter (continuity??)
5) Leave it alone unless that deviation means damage to the body.
6) Right way to adjust is: Closed, you already done the job. Open, plate is parallel to air flow, no less, no more. To adjust this position you need another people pressing the accelerator pedal to full throttle and in the meanwhile you adjust the bowden cable screw until this parallel position is reached.
jimoreno
Posts: 1600
Joined: Aug 30, 2007 9:31 PM
Location: Land O Lakes, FL

Re: Throttle body cleaning and a few related questions.

Post by jimoreno »

Not to steal OP's thunder but how do you guys with Motronic 1.3 / B35 engines adjust the GPS? There's no definitive click as I believe the round connector TPS is a rheostat. Right now I have it full to the right but if there's a better way I'd like to know it.
Aldo525
Posts: 459
Joined: Mar 24, 2021 3:04 PM
Location: Puerto Varas, CHILE

Re: Throttle body cleaning and a few related questions.

Post by Aldo525 »

jimoreno wrote: Apr 24, 2025 12:03 PM Not to steal OP's thunder but how do you guys with Motronic 1.3 / B35 engines adjust the GPS? There's no definitive click as I believe the round connector TPS is a rheostat. Right now I have it full to the right but if there's a better way I'd like to know it.
 
 
 
 
 
 
Round connector TPS like this you mean???....internally is the same as the square connector;i.e, click when throttle is opened slightly.

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Freight
Posts: 95
Joined: Dec 26, 2024 3:19 PM
Location: NY

Re: Throttle body cleaning and a few related questions.

Post by Freight »

Aldo525 wrote: Apr 23, 2025 6:12 PM
Freight wrote: Apr 23, 2025 2:07 PM
That’s what a figured. There’s always gonna be vapor in the crank case, and it’s gonna coat the intake, but I’ll admit this is the first time I’ve ever had a throttle body off an engine so I wasn’t entirely sure what to expect. It was truly just a misty coat, and like I said not enough to pool and run back down the intake past the breather.

thanks for easing my nerves 😬 
My comments:

3) Gasket is very cheap, so it's better to replace with a new one to avoid vacuum leaks.
4) Normal, it's the way that TPS works, but the "trigger" you mention is the "beep" of a multimeter (continuity??)
5) Leave it alone unless that deviation means damage to the body.
6) Right way to adjust is: Closed, you already done the job. Open, plate is parallel to air flow, no less, no more. To adjust this position you need another people pressing the accelerator pedal to full throttle and in the meanwhile you adjust the bowden cable screw until this parallel position is reached.
Yes, the tps is dialed in perfectly - confirmed with multimeter.

the deviation is very lightly marring the body in just that corner but it doesn’t cause any friction. Only about 3-4mm of potential contact. It’s not much more marred than the ring on the body where the plate is closest when shut but that isn’t from contact, just 163k miles of whatever air/vapor/particulate being sucked through that tiny gap. 

I’ll get someone to help me adjust that with the cable. It’s only a couple degrees past parallel so not a big deal at the moment.
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