paperclips43

99 A6 AHA 2.8 C5
I did some logs with the vag come during cold start and idle and some driving just around the block. Hoping to solve my slight rough idle symptoms are"

Cold start sound good at idle but RPMS do slowly drop instead of all at once like it used to. Used to idle at Eleven Thousand and then when the Air pump kicks off it drops to 800 but now it will just slowly drop down and down and then settle at 800 when pump is off and wander around 700 slightly.

But once it is warm and driven it will wander a lot more and sound a bit hard but nowhere close to stalling.

I did a smoke test on the pcv system and it seems fine but I do suspect the suction pump. I have a total of 4 suc pumps some i got at old junkyards. Two of them Audi and two of them Uroparts and they all seem to behave a little different. Some hold vacuum with my hand held pump and some you can blow both ways and some only one way. Some look damaged inside its hard to find out the exact way it is supposed to behave. I swapped them and tried them all and it didnt seem to change the idle issue. Maybe they are alll bad?

I tested my combi valves and they were not good I took them off and cleaned the **** of out them so much carbon came out. I got them both to respond properly to vacuum and hold until released. I was really hoping that was going to solve my idle issue as they were an absolute PITA to take off and put back on. I seriously had a mental breakdown on Bank 2 and if anyone ever does them on Bank 2 I would recommend removing it first by the two allen bolts that are upside down them remove elbow connecting to bank 2. Attach them together and bolt it back to the engine by the bottom three bolts securing the elbow. Trying to secure it by tightening those two upside down allens was a stressful experience, removing them though not as bad.

Ive attached 5 separate logs i took that I dont completely understand Im learning though. Oh and I have done a few Throttle Adaptations as well but still no change.

I ordered a bladder to attach the smoke tester to the tailpipe as I am now suspecting an exhaust leak. Any thoughts or advice is most welcome.

No DTC codes btw.

georgeb944

I would do the smoke test at the intake boot between the MAF and the throttle body.

You could use a device like this to make the connection.

http://www.vaglinks.com/Docs/Audi/C5...eakTesting.pdf

paperclips43

Ok thanks for that link. Good info to have.
This should work then right?


Also I do have the 2.8 but the theory is still the same I’m assuming?

A couple things about going in through the intake confuses me. I need to have the throttle plate open right? Which can be done by disconnecting the fuel pump relay and having someone press the accelerator..

Second if I have smoke and air pressure going in through the throttle body going into the intake manifold and into the cylinders. If the exhaust valves are open wouldn’t it just travel through and out my tailpipe?

Do I need to rotate the crank to a certain position so the exhaust valves are closed?

I may not understand the mechanics yet entirely.
I’ve only gotten as far as taking my intake
manifold off and valve covers so far.

and here is a link to the above item pictured that I ordered.

https://www.ebay.com/itm/40402860332...mis&media=COPY

georgeb944

If the exhaust valves are open, then the intake valves must be closed. Hence, no leak.
LIkewise, if the intake valves are open, the exhaust valves are closed...

The crankshaft can be at any point for the test to work.

The device might work, if it can fit securely in the intake boot. It might not be a tight fit and would then not work.

paperclips43

Ok I made a cap just like in the pdf you posted. Sealed some NPT fittings on there and upgraded my smoke machine. Attached it to the elbow before the throttle body. I get a tremendous amount of leaking smoke from the throttle body elbow boot connection. Looks like it is creeping out from the gasket. Thing is I just replaced that gasket type thing. Its brand new but it does fit on there a bit loosely. I always thought it silly that the only way the elbow attaches onto the throttle body is one long screw that threads into the throttle body It doesnt seem like thats enough to hold it on. Also I am for sure opening my throttle plate because i can open my oil cap and I get smoke, take off the vac line for the fuel rail and smoke pours out.

Of course this is positive pressure that I am sending in when normal operation it is going to be negative pressure which could pull the gasket tight and not be leaking air.

Anyway is the likely the source of my issue? Whats the fix?

I will probably remove the elbow and attach my smoke machine directly to the throttle body next to make sure nothing else down the line is leaking that is being masked by the massive leak through the TB and Elbow mating area. But it doesnt seem likely, as still a good amount of smokey pressure builds up even while leaking there which is evident when I pull open up a vac point down the line. I get a rush of smokey air pop out.

Also My Lamda is -10.2 and that means it is running really rich right?

paperclips43

Also this is one area that is different than the 2.7. I see a lot of upgraded hose and clamps that attach to the throttle body for the 2.7 but nothing for my 2.8 :/

georgeb944

Any place that the smoke leaks out is also a place that false air can enter, causing a lean mixture (which the fuel injection map will try to compensate for as much as it can.) Vacuum leaks tend to cause symptoms that are more noticeable at idle (when the throttle is closed and the vacuum is supposed to be at maximum).

When your car left the factory, there were no leaks... fix your leaks and it is likely that you will fix your idle problem.

paperclips43

I found this thread but didn’t realize it was for a 12v and the throttle body was different until the last minute.

https://www.audiworld.com/forums/aud...asket-2081856/


I basically did exactly what he did thou which was wrap phone cord in the gasket between the intake plenum and the TB. It was super tight getting it on there and I had to screw it on basically turn by turn.

I think it’s fixed now thou. Idle was good. And I blipped the throttle a few times
and it didn’t fall low like normal.

I’ll run a scan later and check my lambda and other measures. Im hoping this will fix the idle drop I would also get when coming to a stop. Especially when going into reverse I would get an idle drop to 450-500. Nothing that felt close to a stall but I imagine normal and healthy idle should never wander not even once. .

“Can’t have no leaks in the pool.” The goal is always perfect numbers across the board. Can’t settle for anything less.

I imagine a lot of people are dealing with a loose gasket between throttle and plenum as there is no common fix. Another route mentioned to solve this issue is to use silicon then let it dry and that should seal it up.

georgeb944

Every Audi or VW owner should have a smoke tester (even a $15 DIY tester) for finding vacuum leaks.