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[Audi A3/S3] Juddering under acceleration, Poor idle


nickthedaddy
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Can anyone help????

I have a 99 Audi A3 1.8T petrol (AGU engine) the car has just done 100,000 miles

I have recently been having an intermittent problem.

I can be driving along normally then for no apparent reason when I accelerate the car hesitates and feels as if its missfiring, it lasts for varying amounts of time then disappears. When the car is stationary with the bonnet up I can see the engine appear to misfire causing it to jerk every so often causing a popping/spluttering noise from the exhaust. This doesnt always happen so cant put my finger on what it is. It doesnt seem to be there when travelling at motorway speeds, only when I put my foot down to pick up speed. A couple of times I have been sat at lights and the revs drop to almost stall point but then it corrects itself. last week it was really bad causing the mpg reading to drop to 14mpg but has gradually risen back to normal since then!

My dad is a retired police mechanic and he cant figure it out. He has a snap on diagnostic machine which doesnt pick up any problems, neither do I get any warning lights on the dash.

I have been trying to fix the problem but I am running out of time, money and patience as it isnt a consistent problem. :ffs:

Not sure if it means anything but it has been worse since I serviced it a week ago, I changed the oil & filter, air filter & spark plugs.

Sinced the problem started I have checked the coil packs, changed the MAF sensor and the pre cat lambda sensor but still havnt cured it!

Any ideas would be much appreciated! Thanks guys!

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I wish I had a fault code to use as a start point but nothing shows up which is why it's trying my patience.

I bought just one coil pack and tried it in each of the 4 cylinders but the problem persisted, I then let the engine tick over and waited for it to misfire before unplugging each pack individually to see if there was any change, doing this only made things worse indicating that the coil packs are working ok.

I didnt want to buy 4 coil packs as I have limited funds and have already spent £160 on parts in the last week with no joy!

I dont know what to try next, I need it sorted as dont have use of another car and cant afford to keep replacing things it could be without knowing for sure!

Thanks for replying, Ill wait and see if anyone has any ideas!

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Hello mate, i just joined this site because iv been meaning to do it for a while and i saw the message your left about the problem you have been having with you A3. From what you wrote it sounds like you have the same problem as what i had a while ago, juddering under acceleration, poor fuel consuption, missfiring with spluttering popping sound from the exhaust.

The problem would sometime come and go but when it didnt go away for a couple of days i had to do something. Checked spark splugs and they were fine, checked the coil packs and they were fine but the coils on the early A3s were a common problem. Checked all wiring and connecters to the coil packs and they were all cool. One of the only things left to check which could of caused the misfiring was the (IGNITION AMPLIFIER) which is located on your standard air box. have you replaced it with a aftermarket intake?

The ignition amplifier takes a low voltage signal from the ECU and converts it to a high voltage signal to the ignition coil which in turn transfers it to the spark plug. A dead one will cause miss fires or not firing at all on one or more cylinders. Its basically 4 transistors, hence the need for it to heat sink agaisnt the air box, and when replacing the airbox for example with a cold air intake the ignition amplifier will tend to over heat causing to be faulty.

I replaced mine for £75 from a friendly car parts dealer but they can cost alot more especially from AUDI and the problem was sorted as soon as i fitted which took like 20 seconds and the problem has never come back since.

So i think this may be you problem mate but before you go out and buy one locate it and disconnect and clean the the connectors abit and try it again, if it doesnt work and you have a few spare pennys replace the ignition amplifier and if it works happy days but if it doesnt cure your problem i suggest your send it back for a refund and get it in a garage. I am 90% sure that is is your problem mate but i am no mechanic but i wanted to try and help you because your problem sounded the same as what i had and it really annoyed me when my car was running like a bag of S**T until i got it sorted. Well look into what i have suggested and i hope you sort your problem.

If you have any problems dont hesitate to message me back i will try and help all i can. I will see if i can get any pictures for you but i am new to this site and dont really know how to do things yet.

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Hello mate, i just joined this site because iv been meaning to do it for a while and i saw the message your left about the problem you have been having with you A3. From what you wrote it sounds like you have the same problem as what i had a while ago, juddering under acceleration, poor fuel consuption, missfiring with spluttering popping sound from the exhaust.

The problem would sometime come and go but when it didnt go away for a couple of days i had to do something. Checked spark splugs and they were fine, checked the coil packs and they were fine but the coils on the early A3s were a common problem. Checked all wiring and connecters to the coil packs and they were all cool. One of the only things left to check which could of caused the misfiring was the (IGNITION AMPLIFIER) which is located on your standard air box. have you replaced it with a aftermarket intake?

The ignition amplifier takes a low voltage signal from the ECU and converts it to a high voltage signal to the ignition coil which in turn transfers it to the spark plug. A dead one will cause miss fires or not firing at all on one or more cylinders. Its basically 4 transistors, hence the need for it to heat sink agaisnt the air box, and when replacing the airbox for example with a cold air intake the ignition amplifier will tend to over heat causing to be faulty.

I replaced mine for £75 from a friendly car parts dealer but they can cost alot more especially from AUDI and the problem was sorted as soon as i fitted which took like 20 seconds and the problem has never come back since.

So i think this may be you problem mate but before you go out and buy one locate it and disconnect and clean the the connectors abit and try it again, if it doesnt work and you have a few spare pennys replace the ignition amplifier and if it works happy days but if it doesnt cure your problem i suggest your send it back for a refund and get it in a garage. I am 90% sure that is is your problem mate but i am no mechanic but i wanted to try and help you because your problem sounded the same as what i had and it really annoyed me when my car was running like a bag of S**T until i got it sorted. Well look into what i have suggested and i hope you sort your problem.

If you have any problems dont hesitate to message me back i will try and help all i can. I will see if i can get any pictures for you but i am new to this site and dont really know how to do things yet.

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Cheers A3 beast, you understand how I have been driven mad by it by the sound of it. I have read about the ignition amplifier on other forums & know exactly where it is. I have taken it off and it is not particlarly dirty although the heatsink paste doesn't make it look clean either. Im tempted to buy another and give it a go in case it has packed up but I know from experience that it isnt always easy to take a part back to a dealer once opened if it isnt at fault. One thing mate, when yours went did it make the engine management light come on or did it throw up any codes (if you did a diagnostic that is) Thanks again for such a detailed post and fingers crossed it will stop me from pulling my hair out! When im a bit more flush I may splash out on one. Take it easy mate!

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Thats cool mate i am happy to help where i can. I didn't notice any engine management light come on through out the whole time i had the problem. i didn't do any diagnostics to see for any error codes. Im pretty sure that is your problem dude but if you have a local friendly garage get him to check the ignition amplifier and the connectors that lead from it to the coil packs for voltage. I think if one or more of the connectors on the coil packs are down on signal or voltage the ignition amplifier is the reason why its not getting the right voltage and signal to spark 1 or more of the of the failing cylinders. You may be able to do this yourself mate if you have a voltage meter. When i had my problem i looked on Ebay for a second hand one off a completely standard car and they were going for around 20 quid but i didn't buy one because i knew what my problem was and decided to buy a new one. There are brand new ones on there and are alot cheaper than from the Audi dealer and other internet stores.

If you cant diagnose the problem yourself take it t a garage mate or i advice you to buy a second hand one off Ebay for 20 quid or less and see if it works. its alot easier to send items back on there for full refunds aswell if it didn't do the trick. If it works then there is no need to buy a new one untill the replacement fails and it only cost you roughly 20 quid. In my opion its worth ago mate. If you cant find one listed on Ebay message sellers breaking A3s and ask them if they still got one which they should have. Also if you have a mate with the same car see if he will let you quickly swap them over to see if it cures your problem. its worth ago and it dont cost you anything unless your mates names SCROOGE McDuck.

Let me know if you still have problems dude an i will try and help, and let me know when your have sorted it and what the problem was. GOOD LUCK

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Right bought an Ignition amplifier module and fitted it yesterday, havent noticed it idleing badly yet but will have to give it time as it is so intermittant. If it starts doing it again I will be stuck as havnt a clue what it could be! May just be my imagination because im looking for a problem but thought I felt a single judder under acceleration yesterday but like I said, time will tell. Ill update the post in about a week with the verdict.

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