Carbon build up in the throttle body

[Sedan]

Hi guys,

I drive a manual 08 sedan and started experiencing an engine knock at cold start. After few minutes of driving the knock disappears and does not occur till the next cold start.

I took the vehicle to a mechanic and found a thin layer of carbon build up inside the throttle body. Did a clean up afterwards and the car drove fine, but after few weeks the knock started to develop once again. I removed the throttle body and saw there was again build up of carbon. Cleaned it up, car drove fine and after another few weeks, knocking and carbon build up again.

If it is relevant, the car is very slow to respond say when you pick up after stopping uphill. It takes that much more time to respond to the pressing of the accelerator.

Could you explain a reason for this scenario please.

Thanks in advance.
Cheers!

[bairjo]

Maybe check and clean pcv valve and egr valve?

[Sedan]

Thanks for the quick reply. I will certainly have these two valves checked.

BTW, mods, why is this thread moved?

[CrankyOldMan]

I have the same problem, but I also have a supercharger. My assumption is that mine is from blow-by (compression leaking past the piston rings) pushing partly combusted fuel through the crankcase (the "C" in PCV"). It eventually causes my throttle to lag, but it's not so bad that I have to clean it every month.

If you want to stop the symptom--and you've checked the PCV and EGR valves--you could install an oil catch can. If it is indeed blow-by, and you want to fix the cause, you would need to have the piston rings replaced.

[Sedan]

I have the same problem, but I also have a supercharger. My assumption is that mine is from blow-by (compression leaking past the piston rings) pushing partly combusted fuel through the crankcase (the "C" in PCV"). It eventually causes my throttle to lag, but it's not so bad that I have to clean it every month.

If you want to stop the symptom--and you've checked the PCV and EGR valves--you could install an oil catch can. If it is indeed blow-by, and you want to fix the cause, you would need to have the piston rings replaced.

Thanks a lot. I will take the car to a garage over the weekend and get these valves checked. Hope it wont go as far as replacing the piston rings.

[bairjo]

Well if the oil changes were done as required...I wouldn't worry about the rings...but I could be wrong....again.

[Sedan]

Well if the oil changes were done as required...I wouldn't worry about the rings...but I could be wrong....again.

I do wish you are right. I have only used Toyota genuine oil and replaced at the correct intervals.

[Bluevitz-rs]

There is no EGR, so when your mechanic tells you it's ok and charges you, he's ripping you off.

[bairjo]

Yup you are correct!...I'll take back what I said earlier...even the part about the rings...

[Sedan]

There is no EGR, so when your mechanic tells you it's ok and charges you, he's ripping you off.

Thanks.
Is the EGR only available in the diesel varient?

And guys, is there a way to test weather VVTI is working properly?

[jambo101]

Hi guys,

I drive a manual 08 sedan and started experiencing an engine knock at cold start. After few minutes of driving the knock disappears and does not occur till the next cold start.



Could you explain a reason for this scenario please.

Thanks in advance.
Cheers!

Any chance this could be a tapping noise rather than a knocking noise? As i;ve experienced many cars that have a temporary tapping noise on start-up, i've been told it has something to do with valves operation before oil comes up to operating pressure.

[Bluevitz-rs]

Thanks.
Is the EGR only available in the diesel varient?

And guys, is there a way to test weather VVTI is working properly?

There is no EGR because of VVT-i. Only way to test is with a Techstream Tool from Toyota.

Piston slap is all you're hearing. It's normal on a cold engine. As the cylinder bore wears, piston to cylinder wall clearance increases and allows the piston to rattle back and forth slightly causing the knocking sound. Nearly every engine will eventually do it. You just need to take it really easy on it until it has had a chance to warm up and expand to close the gap.

[Sedan]

Thanks all. Really appreciate your input.

Anyway, it is not the noise. The hesitant knocking when pressing the gas pedal. I'm concerned as to why carbon is building up in the throttle body continuously. This knocking may be a sign of worse things to come. Hence the effort to find out the cause.

[Bluevitz-rs]

Perhaps a picture could better illustrate the carbon buildup.

[Sedan]

Hi again.

I removed the PCV valve myself just after a ride in the morning. There was fresh oil on either side of the valve, I shook it, and was able to hear a rattling sound.

Googled and found out that if the rattling can be heard, the valve should probably be OK. But why the oil?

Any suggestions please.

[dj92]

The oil comes out because it is spraying around in the engine while running.
It depends on the manufacturer's efforts how much of it comes out.
EDIT:
I've taken apart mine earlier this evening (it's 4:03 am local time now), but the oil did not make it to the throttle at all.
The throttle itself was covered with a thin layer of carbon dust, but it was totally dry, so I did not clean it now.
I've hit 40000km tonight :D

[Sedan]

When inspecting, I saw the butterfly valve of the throttle was not completely closed even when the power supply was disconnected. Could there be something wrong here?
I ran a scan of the vehicle afterwards and the absolute throttle position at idle (600-700 rpm) was about 17%.
Do you guys see anything wrong here. I can attach the entire scan report if it helps.

[Bluevitz-rs]

This is all normal operation. Stop worrying.

[Sedan]

This is all normal operation. Stop worrying.

Thanks.:smile: