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John, ASE Master Technician
Category: Audi
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Experience:  ASE Certified Master Technician, ASE Certified Service Consultant, 22 years professional experience
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Audi TT Quattro: A very good friend of mine is going crazy

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A very good friend of mine is going crazy trying to figure out what is wrong with is son's 2001 Audi TT Quattro,6 speed manual tranny. He states the car shakes and that does not produce the hp it is supposed to. Car is 120K miles. Took car to the dealer who changed the tranny mounts(?) and problem not solved $500 later! Last week took it to an indy mechanic who diagnose fuel injectors to cilynders 1 and 4 not working at 100%. Replaced them,but on the way home he noticed the car still shaking and not with full power. Stretched it to 110mph on highway and Check Engine Light came on. Waiting to take it back to mechanic tomorrow to have it checked. Mechanic had said that some carbon build up on intake manifold(?) or even on exhaust system(cat converter) was possible to take some type to dissipate and regain full power and shaking desappear. Can you give me some ideas on how to help him trace the problem? This before the mechanic reads the code(s) tomorrow?
Hello. Misfires due to ignition coil problems and mass air flow meter problems are common in these cars and could be the problem here based on your description. However, the real piece of that will help is knowing what code has set. Please let me know what code is found and I can be more help. Sorry to not have more info for you but I think I need a bit more information. If the shop finds misfire codes P0300 through P0304 and recommends sparkplugs and coils, have them also check the wiring to the coils for damage or poor connections at the coils themselves.

Good luck, I will be watching for a response.
Customer: replied 2 years ago.

ok will revert tomorrow and let you know after code(s).tks

Looking forward to it.
Customer: replied 2 years ago.

Hi John.Got the code P1128 - Manufacturer Controlled Fuel and Air Metering. So it sounds like it's the Air Mass Meter not working properly, am I right? The coils and spark plugs seem to have been changed not too long ago. Mechanic is going to change the AMM and see what comes out of it. If you have any other tip or something else to check pls let me know. I'll revert with results. Tks

This code is common for vacuum leaks relating to the Turbo Recirculation valve. You may want to pass this along before you pay for a Mass Air Flow Meter:

1. Inspect the vacuum lines going to the recirculation solenoid for turbo N249 located on top of the engine. The N249 solenoid controls vacuum to the mechanical boost recirculation valve located in the intake duct ahead of the turbo. Manifold vacuum must be present to the N249 solenoid.

2. Connect a full function Volkswagen compatible scan tool. Under address word 01 "Engine Electronics", press 03 for the function "Output Diagnostic Test Mode". Proceed through the test until the recirculation solenoid for turbocharger N249 is activated. The N249 solenoid must click.

3. If the N249 solenoid does not click, disconnect the connector from the valve, and using a Digital Volt Ohm Meter (DVOM), measure valve resistance. Specification is 27-30 ohms.

4. If the N249 solenoid is not in specification, then replace it.

5. If the N249 solenoid clicks and has a normal resistance reading, insure that it passes vacuum to the mechanical boost recirculation valve in the intake duct ahead of the turbo inlet.

6. The mechanical boost recirculation valve is opened by vacuum and functions as described in the Tech Tips section. Be sure the valve opens fully and flows when vacuum is applied and that it does not leak when no vacuum is present.

The boost recirculation valve is a normally closed valve that is opened by a vacuum signal to recirculate turbo boost pressure back through the turbo during deceleration. This action ensures excessive boost pressure post turbo does not back up and stall the turbo impeller during a hard deceleration. In addition, the recirculation of boost keeps the turbo spun up to minimize turbo lag. Early systems are vacuum operated only while the later systems use a Powertrain Control Module (PCM) duty cycled solenoid (the N249) for fine control of recirculation amount.

Checking the Mass Air flow Meter specs with a vacuum leak will often lead to incorrect results. I think this is worth a look.

Customer: replied 2 years ago.

Your explaination seems to be very complete and Im going to pass it to the mechanic before he changes the AMM. I'll revert after tests. Tks again

Great, I will be watching for it.
Customer: replied 2 years ago.

Hi John the mechanic had already installed a new AMM. However I dont think he solved the problem with it. The car still shakes,specially at low RPM(between 1,000 and 2,000). Above and below that range it's not noticeable...As far as power I cant tell if there was a boost with the new AMM. Waiting my friend to come home and test it. If he is not satisfied mechanic said he would put the original AMM back and didnt have to pay anything for new one. Then "I have to convince" to do the tests you suggested and if N249 solenoid needed will sure be better paying around $25 for it than $400 for AMM. Anyway I tku for your help and pls let me know if anything s/b tested so I can close discussion and ACCEPT yr answer.

If he is willing to gamble a $400 air flow meter then maybe he should just replace the N249 valve and see. It is a very common failure for this code.

Let me know how it turns out.
John and 2 other Audi Specialists are ready to help you
Customer: replied 2 years ago.

I will let you know what he wants to do. My friend does not want to spend more money with a non solved problem.Tom mechanic will have to replace AMM with original and try the N249 if he wants. If not will go another route. Tks again and I'll ACCEPT now.

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