View Full Version : C5 A6: Cleaning throttle body on 2.8 30V ACK engine

09-04-2008, 02:22 AM
Car is Audi A6 2.8 30 V Quattro from 1997 with 193PS ACK engine. Although this is my fathers car I am doing all the maitenance on it. Unfortunatelly this is the worst car I have ever driven. Built and material quality is very poor so there were lots of things to take care of.
Latest problem was unstable idle. When throttle pedal was released, revs would fall to 400rpm, then rise againg, fall, and so on... After few such cycles idle revs would stabilize again.Problem was this is not always present thing, but would appear from time to time. I thought problem could be with idle valve, but this being ACK engine it has no separate idle valve, but motorized butterfly valve inside throttle body. So, all idle, choke and other regulation is done by electric motor attached to butterfly valve.
I have decided to take look if something there is wrong.

Turn 4 screws (1) 90 degrees to either side to pop up, and lift the cover

Release the intake pipe clip (1) and unscrew three 10mm bolts (2) from mounting

Disconnect connector (1)from vacum valve, release the thin pipe from its holder (2) and lift mounting to the left side. Be carefull as vacum pipes are made of VERY thin ruber.

Disconnect intake pipe sensor (1), release clips from vacum pipes (2) and move pipes to side. Disconnect throttle body connector (3)

I was surprised to see that intake pipe is simply inserted into throtle body and secured with one screw; with only rubber ring shaped seal ensuring sealing. Remove screw ( 5mm Allen bolt).

Disconnect intake pipe and disconnect engine breathing pipe.

Intake pipe removed. I discovered small oil puddle in the bottom of the pipe.

Remove tank purge pipe (1), shown already removed, and undo 10mm screw holding throttle body.

Beside one screw from previous step, three more screws are holding throttle body. They are hidden behind so you need to feel them. Note one bottom screw is holding grounding wire.

With all four screews removed, lift the throttle body. Note that bottom two screws are also holding pipe.

Disconnect the throttle pedal steel rope

This is how it looks inside throttle body. Some oil residues and some carbon buildup was found, but in my opinion not enough to create problems

After cleaning with carburetor cleaning spray and cloth. Looks much better.

I decided to open electric section. Use the torx bit for this. everything looks nice and clean here.

To be sure, I have sprayed some Contact spray on sliding contacts seen here.
There are two of them, one for foot operated system and other for motorized.

Reassemble in reverse order.

Although I have not found any sure evidence of any malfunction throttle body was cleaned and checked to eliminate it if problem should appear again.

Hope someone will have use of this DIY.