Rough Idle Need Help Running out of ideas

**rickybotts_123** · 18-10-2015,07:48 PM

Hello I am new to the forum but have been doing a lot of reading up trying to diagnose the issue i have. I have recently purchased a A4 b6 quattro avant 1.8t. Its a 2003 with 108k and full service history.

The car runs great and gives good mpg. The idle however has been very rough. I started with the simple stuff and replaced the plugs. I noticed whilst changing them that the old one were full of oil. Having read up i then went and bought the rocker cover and plug gaskets and replaced them. I also replaced the air filter and also a cracked pipe i found from the secondary air unit to the air box. This didnt have any effect. I then ran the engine and unplugged each coil pack and the car ran worse. I also disconnected the MAF sensor and again the car ran noticeably worse.

I then went round each hose i could see and clamped them off to see if it made any difference, it did, it was the one that leads to the Y shape suction pump purge valve at the back off the block. I replaced that from audi and also the pancake valve. The car then started to tick over correctly and still drove well however when it was fully warm it would idle around 1100-1200rpm.

Also the EML light came back on and i was getting P0171 but the car idled a lot smother. Having read some info today I took the throttle body off and cleaned it all inside. The car started fine but the lumpy idle returned, which it hadnt been doing for a few days.

I let the car run and there are no codes or EML and the car also drives well. However if I leave it to tick over and the throttle is pressed and the car is left to return to idle i get a flashing EML and generic p0302 p0304 p0300 pending codes and it sounds like its going to stall.

I have tried to find vac leaks by spraying carb cleaner whilst the cars running but cant find any. I also only have a cheap OBD2 reader and dont have access to vag.com.

Anyone got any ideas or is it time to take it to a garage? Also could the rough idle be from me disconnecting the TB and not resetting it? Ive read that this can only be done with VagCom?

Thanks Richard

**rickybotts_123** · 18-10-2015,08:33 PM

From hours and hours of more reading I am going to look at replacing the crankcase breather valve, hope this may sort my initial issue with the lumpy idle. The one question I need help with is,

Would a throttle body which hasn't been reset with vag.com cause a lumpy idle? or has the original problem just returned and this is a coincidence?

**pauldazzle** · 19-10-2015,10:07 AM

ECU will adapt the TB over a few driving cycles, VCDS/vagcom just does it in a few seconds .

**rickybotts_123** · 19-10-2015,11:38 AM

Ok thanks for that. Ordered the crankcase breather and currently waiting for the throttle reset now so hopefully it will sort it

**rickybotts_123** · 19-10-2015,04:02 PM

Just a quick update if anyone else stumbles across this thread. Had the throttle body reset today and the guy confirmed that the crankcase breather is faulty. He also said that once the new one is fitted that will sort the car out. It's the little green valve which sits in a pipe under the manifold (035 103 245G) part number.

I used autotechnica on Calvert Lane, Hull. They were absolutely spot on. I just turned up and the fitted me in. Took him ten minutes or so and he showed me where faulty valve was all for £27. Ordered valve from Audi so will report back tomorrow.

I would definitely check this first before chucking loads of parts at the car. There is plenty of info on it. Just wish I'd of found that first.

**Crasher** · 19-10-2015,05:51 PM

It is a very common problem on the A4 1.8T.

Item 6

**rickybotts_123** · 21-10-2015,09:10 AM

Right got the valve and replaced it and when first installed the car was still idling like crap. As a shot in the dark I did the ignition on whilst holding the accelerator down and then ignition off and waiting two minutes and the car started to idle a lot more stable and was noticeably more powerful on pick up. When cold it idles high for a few seconds as it should and returns to a very stable 800rpm. However when warm it idles around 1000rpm and fluctuates between that and 800rpm and sometimes rises to 1100rpm but settles around 1000rpm.

I have also noticed that when changing gear particularly in 3rd the revs hold for a second before dropping down as the clutch is engaged. This could be down to me as I have only had the car 2 weeks and the clutch pedal is higher compared to my old car. Clutch is fine though with a nice biting point etc and no slip but thought it worth mentioning.

I have read that sometimes the clutch pedal switch can cause these symptoms?

Also my data cable should come today and I have downloaded the free/lite version of VCDS. Is there any values I should be paying attention to/to try and pin point this issue? Also I had previously done a ECU reset so could this just be the re-learning process?

I know in my Ford Mondeo it took sometime for the ECU to relearn and erratic idle readings were common for so many engine cycles.

Or could it simply be another vacuum leak? I have also notice that the injector seals are leaking so I have ordered them.

Any advice would be great.

**Crasher** · 21-10-2015,10:28 AM

You cleaned the throttle body didn't you? You need to reset the learnt values and adapt the throttle body and the freeware version of VCDS will not do that, you have to register it which costs $99. You can check the clutch pedal switch in Measuring blocks, group 060 zone 3 bit 3 if I remember rightly. Bits 1 and 2 are the brake pedal switch.

**rickybotts_123** · 21-10-2015,11:58 AM

Yes when I had cleaned the throttle body I took the car to a VW/Audi specialist who reset the throttle. The car then drove correctly but wouldn't idle right until I replaced the crankcase breather. As stated that has now been replaced and the idle is stable although somewhat high. Are you saying the thottlr will need resetting again via software? Thanks