devinsixtyseven

How does one establish if the combi valve needs replacement? Can they be cleaned and re-used? 150$ part, to replace each one.

135k on the engine.

TIA.

-Sean

4Driver4

There is no EGR valve; it's a combi valve.

You should be able to test operation with a hand-held vacuum pump. Apply vacuum and see if it opens.

Prospeeder

its not an EGR!!!! lol everybody keeps calling them that. Its an Air injection valve. basicly just apply vacuum to it and it should hold and not leak down. Thats about it


EGR= Exhaust gas re circulation. Thats not whats happening. Air is being pumping into the exhaust to warm up the catalysts. EGRs bring exhaust gasses into the intake to displace air in the combustion chamber.

jcman

Yep and both are subject to carbon deposits that restrict or hinder them in use.

devinsixtyseven

Well, this vacuum-actuated diaphragm valve is full of soot and I did find moisture inside...so I picked up a can of TB cleaner and I'll rebuild the SAIP too.

For the record, the little 50$ vacuum gun sold by NAPA is a piece of **** and I'm taking it back. It wasn't of any use checking the valves anyway, hose too big and I didn't have anything on hand to make an adapter.

The combi valves can be checked by mouth (yep). They require very little vacuum to open, or at least mine did. Good thing I don't live in California, I'm sure it would've given me cancer. :P

rohit13

I checked mine in my 2.8 by mouth.

I opened the vacuum line between the two combi valves (later put a $.99 rubber hose between them to reconnect)

When the car is from a cold start, the pump should start and from the vacuum line you should be able to blow air inside the line for about 1 min. After that the valve closes and you will know. It closes as the pump shuts off so listen to the pump.

jcman

Hey Sean, not sure were I got this to give the credit might of been from AW.

Happy T-Day!

John V.


Secondary air injection seems to be something sooner or later every Audi owner has a problem with. Let me run down the symptoms and then the steps to fix them. This should be the definitive guide on how to repair the system. If you had an issue & repair that wasn't covered by this guide, please shoot me an email.

The first and most common problem is broken/frayed vacuum lines that run to the kombi valve(s). If you have a 2.8, there was a recall on most of them to update the vacuum lines to beefier lines. If this wasn't you, or you have a 1.8, it's still easy to check the vacuum lines. If they even look suspect, just replace them. Vacuum hose is cheap enough and easy to change out. Vacuum lines don't last forever, and heat/age will wear them out.

The next thing to check for is an air pump that flows properly. With VAG-COM there are self diagnostic tests that will cycle the air pump on/off. If it makes a high pitch noise sort of like a jet engine, it may be due for replacement. The air pump typically kicks in when the car is running and idleing. It won't run constantly, usually for about 10 seconds and then shut it off. It's purpose is to pump air into the exhaust which helps improve catalysts when the cat isn't fully up to temp. I've even seen mine run even when the car is fully up to temp. YMMV.

Next on the list to check is the kombi valve(s). You can try and check for their functionality while still on the car, but this may be hit or miss. You need a hand vacuum pump to do this. Use the vacuum pump and pump it up to about -20. If you suddenly release the vacuum, and can feel/hear a nice little thunk from the valve, the diaphragm is probably fully opening and closing. If you don't hear or feel it, it could be sticking. What you want to do then is remove the kombi valve from the car. Use some brake cleaner, and spray it out with the valve both open and shut (use the hand pump). You should have a lot of carbon build up wash out. Operate it off the car and see if you can get smooth operations in the opening and closing. If you do, the valve is probably fine and you saved yourself from buying a new valve. If you are at this stage, it's best to engage in the next repair I have listed.

Carbon build up in the kombi valve exhaust passage is probably the hardest to diagnose. I have yet to see any Audi technician troubleshoot this or even attempt a guess at this could be the problem; but it was an issue on my car. I was able to track this down, but it took a little while. When my air pump ran, I could feel the idle get a little rougher. What I ended up doing was hooking only 1 kombi valve up at a time to the vacuum solenoid to see if I could figure out what side was the culprit. This worked. I was able to get a rough idle on 1 bank, and not on the other. Once I took off the kombi valve, I used a coat hanger to clean out the carbon in the air passage. I could feel a sizeable blockage near the entrance. I then used brake cleaner to clean the passage even more. Brake cleaner does a great job at disolving carbon. Use some spare vacuum hose (hard nylon line if you have it) to shove in the passage. Use the straw on the brake cleaner can, insert it in the hose, and spray away. Follow up with more coat hanger cleaning. Be careful not to break anything off or get something stuck in that passage way. If you do, you'll basically have to pull the head to try and get it out of there.

The last thing potentially that could be a problem is the solenoid for the vacuum lines. I have yet to seen these fail. The 2.8 has two of these actually. One for the kombi valves, one for the intake manifold. VAG-COM in it's self test mode will test these and you'll be able to hear them working.

So to summarize, check the vacuum hoses and replace first. Then check the air pump. Then check the kombi valves and carbon buildup.