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Idle search, runs bad. 132,000. 2.8l. Audi A6 Quattro 2001.

Idle search, runs bad ...

Idle search, runs bad

Mechanic's Assistant: How many miles are on the car? What size is the engine?

132,000. 2.8l

Mechanic's Assistant: What is the make/model/year of your car?

Audi A6 Quattro 2001

Mechanic's Assistant: Are you fixing your A6 quattro yourself? What have you tried so far?

Yes. Scanned it

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Customer reply replied 1 month ago
Codes, 17831, 17819, 17521, 17539, 16684, 16687, 16686, 16689, 17544, 17546, 16891, 16688, 16690, 16685,
Answered in 4 hours by:
4/11/2018
Matt
Matt, Engineer
Category: Audi
Satisfied Customers: 23,069
Experience: Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
Verified

Hello and welcome to Just Answer

OK thats quite a collection of codes

so I'd begin by checking that the ECM has 12V on its fuse and relay and that the battery voltage is at least 12.5V with just the ignition on and engine off, and then check it rises to 12.7+V with a running engine and check the battery connections both ground and positive are both clean and tight

as well as checking the ground connections to the chassis

also check for an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

Air leaks are very temperature dependent as gaps can open up as things expand with temperature so depending on how the leak occurs ( on a hose joint with a clamp expansion will help seal and on a vacuum hose expansion will make a leak worse) so leaks can be better or 1 vacuum leak path that you won't find with the above test is if the brake servo is leaking
so try clamping off servo hose to see if this has any effect

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.

if the engine condition is the same then chances are the meter or the connection to it is faulty

It’s also worth cleaning the MAF sensor wires, as they can get coated with dirt over time which then offsets the reading

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Thanks Matt

Matt
Matt, Engineer
Category: Audi
Satisfied Customers: 23,069
Experience: Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
Verified
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Customer reply replied 1 month ago
I didn't get a chance to get to it today, but you've given me a great deal to work with and I'm happy to rate you service. Thank you so much.
Customer reply replied 1 month ago
Matt, no response from flammable spray to check for vacuum leaks. I did find a cracked hose in front of the check valve, repaired that but still rough. I disconnected the MAF sensor connector and it immediately settled down and ran good. Am I on the right track?
Customer reply replied 1 month ago
Matt, I sprayed the MAF sensor with cleaner and it looks like that was the fix. There's a little dust inside the tube to the TB. Could use a fresh air cleaner and I'll make sure the air cleaner housing seals up. Thanks for your help though. That's a bunch of good info.
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Matt, Engineer
Category: Audi
Satisfied Customers: 23,069
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Experience: Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing

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