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Audi A3 1.8T AGU violent judder/lurch under acceleraration


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#1 nickthedaddy

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Posted 21 September 2010 - 08:53 AM

Hi guys,

I have Another problem with my Audi A3. Its a 1.8T AGU Engine with 102,000 miles on the clock.

Its hard to explain but it every so often when I accelerate hard from a slow speed the car violently jerks, almost as if I had jabbed the brakes. It feels like the car is trying to stall but then picks itself up and is fine for a while, it also seems to do it when I am only just touching the accelerator at slow speed. It isn't a continous jerk when accelerating hard, just one big sort of "lurch" but when only slightly accelerating it carries on for longer until I accelerate a bit more or change gear. I have only really noticed it in 1st and 2nd gear, it seems fine at high speeds in the other gears.

Due to just buying and doing up a house I cant afford to take it to a garage, my old man who is a retired police mechanic can't figure it out so it's doing my head in!

I have tried various things to sort it, Maf sensor, Lambda sensor, Ignition amplifier module and tested the coil packs but have had no joy! The car is regularly serviced and was serviced approx 6 months ago which included oil, all filters and spark plugs etc.

Any help would be MUCH appreciated!

Thanks Nick

#2 p_gliddon

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Posted 21 September 2010 - 11:37 AM

Did you replace the MAF or just clean it? Try disconnecting the MAF and see if the problem continues.

Could try cleaning the throttle body as maybe that is sticking around the closed position?

Have you checked if the diverter valve? Remove it, push the diaphragm up and finger over the small hole on top. When you release the diaphragm it should create a vacuum else it needs replacing. Part number ending 710N is the revised part so if you don't have this one it might be worth replacing anyhow. The DV affects the low boost so could be the cause.

#3 nickthedaddy

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Posted 21 September 2010 - 12:18 PM

I replaced the MAF and the throttle body has been cleaned mate.

I did wonder if it could be the DV valve, would this give randomly occuring problems or would it be fairly consistent? Would it cause a problem when the engine is just ticking over as the car was running rough a few months ago and hasn't really stopped. Also I dont suppose you know if its a drastically expensive part to replace?

Thanks for your reply!

#4 p_gliddon

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Posted 21 September 2010 - 01:37 PM

I replaced my DV recently with an OEM 710N one and it was somewhere between £20 and £30. If its never been replaced it is probably worn out anyhow. I'm not sure of the exact symptoms but the test i mentioned is fairly conclusive as to whether its working correctly.

Have you had a look for split vacuum hoses. Try spraying carb cleaner with the engine running and see if there is a change in engine revs. If so prob a split. Hard plastic hose between the brake servo and the inlet manifold is a common one to split at joints. Feel around the outside of the plastic joint. Vacuum hoses under inlet manifold can be a cuplrit too.

Could be coolant temp sensor? Do you have black or green one? Green one is the revised part.

Google 'TTweakers guide'. A good pdf for diagnosing 1.8T engine problems...

Next step would be try and get VAG COM and run some tests

#5 nickthedaddy

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Posted 21 September 2010 - 06:31 PM

Could be loads of things I guess! I have the new green temp sensor already so guess its not that! I have checked as best I can for split hoses but as you know its a bit tight in the engine bay...I havent tried the carb cleaner trick yet though so that might be an idea. Where abouts is the diverter valve? I have the Haines manual but it doesnt call the part a diverter valve from what I can see. Theres an air inlet valve and secondary air inlet valve but nothing called a diverter valve. There are a couple of bits connected to the air pipe from the filter housing or am I in the wrong place?

Thanks for the advice mate, when I get chance I will look into it!

#6 nickthedaddy

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Posted 21 September 2010 - 06:42 PM

I also noticed tonight that the average MPG reading on the digital display dropped right down and is gradually building itself back up again.

#7 p_gliddon

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Posted 21 September 2010 - 07:46 PM

Did you reset the ECU after you changed the MAF? Disconnect battery for 15mins to reset as this clears the ecu learning of settings for a failed MAF. After reconnecting switch on ignition and wait. Should hear a whining noise from the TB alignment. I think you are supposed to wait 5 mins but might want to check this.

DV- yes you are in the right place. Large hose in the side of the black cylindrical unit and one out the base. Small vac hose in the top which controls the valve. Takes air from downstream of the turbo and returns it to the air pipe from the filter housing.

Does your engine keep a constant temp?

#8 nickthedaddy

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Posted 21 September 2010 - 07:56 PM

Great, I know the one, it has a metal "crimp" clip on the top which holds the hose on I believe. The other part I thought it might be only has 2 hoses so It must be the one you mentioned. Yeah my dad reset the ECU as far as I know. The car seems to take a while to get to temperature, even when the weather is good although It seems to stick to the correct temperature once it gets to it....unless I am imagining it!

#9 p_gliddon

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Posted 22 September 2010 - 06:26 AM

If the car is taking longer to warm up then it will need a new thermostat. Has it ever had one in the life of the car? Age or a waterpump failure can kill them. Located in behind the back of the alternator and make sure you disconnect the battery before replacing as the alternator is 'live'.

#10 nickthedaddy

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Posted 22 September 2010 - 09:08 AM

Hasn't had a thermostat since I have had it, dont think the previous owners had it in the service history either.

Wish I could find what the problem is, im gonna check the dv valve when I get chance but knowing my luck it will be fine so will need to keep trying!




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