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Mike, Technician
Category: Audi
Satisfied Customers: 39198
Experience:  Tech Expert
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Hi I have a audi a3 1.8t AGU - - - DBZ. 110KW /D3 M5S 11/97

Customer Question

Hi I have a audi a3 1.8t AGU - - - DBZ. 110KW /D3 M5S 11/97 that started running rough on idle only, misfiring badly at idle as if not running on all cylinders. Then this progressed to serious misfiring whilst driving like riding a rodeo bull. I replaced all the plugs as thought plug dead, also replaced fuel filter(was very dirty and not replaced for yonks of years, not solved the problem. Had car plugged in to check for codes but no codes appear. Local mechanics in dublin checked coil packs on all 4 cylinders and thought they were OK. Car run on one cylinder at one time with 3 coil packs disconnected. Mechanic found a vacuum hose under manifold on engine totally corroded and broken and replaced with another old pipe. The pipe wall was too soft and we're sucked in not allowing suction. Replaced with heavier pipe. This dampened the severity of misfiring and improved idling greatly. Problem not solved however. Sometime the car will run absolutely perfect, but irregular intervals car malfunction with misfiring. Looks like misfiring gets worse and intervals between good running gets shorter. Mechanics discovered engine light has been disconnected from dashboard. I drove this car about 60k with no problems so not sure that's relevant?
Submitted: 3 years ago.
Category: Audi
Expert:  Mike replied 3 years ago.
Hello and Welcome..

My name is MIKE - Im happy to help you ..

The first thing to mention is that these are very susceptible to not only coil pack troubles / failures - but also , bad wiring connections / broken wires - where the wires plug on to the coils. You need to individually peel back the insulation a couple of inches up the loom from each coil and check for any such bad wiring - not to forget to check the wiring connectors - wires to the connectors - and pins... Again - these are common so careful checking needs to be done there as above.

If all is ruled as ok, then given the lack of servicing this engine seems to have had from what you say, I suggest a very careful check of all the inlet side of the engine - even a small inlet leak caused by a bad pipe / tube - perished piping or loose fitting - anything like that will cause this - you need to check it when its doing it as well. You can use a spray like wd40 or other to spray around the joints /seals / gaskets etc to find any such leak - anything like that will cause such issues.

Other than the above - check the wiring to the injectors in the same way as the coils. If nothing is found - I would suspect you have sticking pintles on the injectors given the state of the fuel filter you mentioned... dirt can have got through to the injectors - so the next best move would be to use a good quality fuel injector cleaner in the tank - and it cleans as you drive.... Give it enough chance to work..

One way of the other as above, you should find this fault and be able to cure it..You at least need to work through the above to make progress on this.

IF you still struggle with it after the above - you need plug in diagnostics doing - not for fault codes as you say there aren't any - but for Live Data reading - that will find the fault for sure that way - but you need to work through the above first.

Do let me know if you need anything else at all - I will be back on later if you need anything more at all -

Kind Rgds - MIKE.

...Meantime..............Please do click on the "OK/ Excellent ratings" for me as that's how Im credited for helping you - Thank you in advance for that...

You can and are most welcome to get back to me anytime you might need - clicking the OK ratings does not close you out at all..

Rgds, MIKE.

Customer: replied 3 years ago.

Hi Mike, I tried all you mentioned but for the injector cleaner. The leads all OK, all vacuum hoses checked, found one small pipe leaking and fixed that. Problem now car kept getting worse and ran real rough. I disconnected the fuel supply pipes to the stainless pipes supplying the fuel to little fuel filter thingy connected to the vacuum system with a small pipe to the underside of the intake manifold. When I removed the wire clip holding the little filter like thing down and removed it, I could see fuel pumping out by switching on or off the ignition with key. Wondering if the whole problem not caused by fuel starvation? Not sure how to test for fuel pump activities?

Expert:  Mike replied 3 years ago.
Hello again Rudi -

Thank you for your reply... Im very sorry I could only just get back to you on this.

Indeed yes it could be fuel starvation - these models - throughout the range are pretty critical on fuel filters - but you said you changed that.

The only proper way to test Rudi is to have a pressure test kit connected up to the fuel rail to see if its in spec - Fuel pressure for the system you have should be - 2.5 ..3.0 bar. You must check this with proper test equipment to be sure as mentioned above. Any deviance in pressure can mean kinked or restricted fuel lines - and also if all else is ok, a faulty fuel pump - that would then need to be further investigated if its out of spec.

Another common issue with these is a faulty ECT sensor - thats the coolant sensor that tells the ECU the temp of the engine - then the Ecu commands the fuelling / ign / timing systems according to the info received from the Ect sensor - if the sensor is therefore faulty at all ( even if its not showing as a fault light or code... you cant rely on that - if at all suspect - replace the sensor - its not expensive and is a very common failure causing these troubles thats another issue to consider. Also - check very carefully , the wiring harness going to the Ect sensor for any issues - they are also a known issue with these for causing troubles.

Its also very important on these that the throttle body is thoroughly clean inside ... If suspect, you should give that a good clean and re try it then.

Another thing that is critical on these is spark plugs - do be sure you have the correct ones for the AGU engine and - that they are gapped correctly. Incorrect plugs and / or gaps - can and will cause bad idling etc.

So work further as above on this then Rudi -

Again - happy for you to let me know how you get on..... For now, I do just need you to click on the "OK ratings " for me please... and I thank you for doing that now for me.

If you do need / wish to get back to me - thats no problem....clicking the OK ratings does not close you out..

Best Rgds, MIKE.