Rough Idle Need Help Running out of ideas

[rickybotts_123]

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]

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]

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

[rickybotts_123]

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

[rickybotts_123]

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]

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

http://i222.photobucket.com/albums/dd20/Crasher1964/A418TBreathervalve.jpg (http://s222.photobucket.com/user/Crasher1964/media/A418TBreathervalve.jpg.html)

Item 6

http://i222.photobucket.com/albums/dd20/Crasher1964/AWTbreathersystem.jpg (http://s222.photobucket.com/user/Crasher1964/media/AWTbreathersystem.jpg.html)

[rickybotts_123]

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]

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]

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

[Crasher]

Possibly, I can end up doing it three or four times during a job and also clearing the learnt values helps.

[rickybotts_123]

Ok thanks for that. Think I'll take it back to the garage and ask them to check it out. It's only £45 for a full diagnostic which is cheaper than chucking parts at it. Thanks again.

[rickybotts_123]

Back again,

Car has been running great however this slightly high idle issue is still present. As I say the car runs great but when coming to a stop the revs hang around 1100 and then gradually drop to 800-900 and sometimes creep back up to 1100.

I had driven approx 400 miles since my last post and was pulled up with the car running when the EML came on and the car started to idle rough again. I turned it off and plugged my cheap obd2 scanner in and again got random misfire codes p0300 p0302 etc and also p0411, a code I haven't had before. Think this relates to secondary air injection incorrect flow. Seen as I was miles from home I cleared the codes and started the car. It again started to idle very rough then clutching at straws I switched it off and did the accelerator pedal to the floor with ignition on for a few seconds and left it off for a couple of minutes. When I started it back up it idled great and I managed to get home.

The car has been fine since but again is idling high.

I have listened for the SAI pump on a cold start and can hear it coming on for a minute or so then switching back off. I have checked both plastic hoses (one of which I had previously replaced) and both seem fine.

I am still convinced I have a vac leak somewhere but have been thrown off track a bit by how the car ran ok once I reset the throttle.

Could it be a bad TB? Or is there any vac lines I should be checking/replacing?

I have read a lot about the combi valve but othescsymptoms aren't the exact same as mine.

Any help would be great.

Thanks

[Crasher]

If you think there is a leak you need it pressure or smoke testing. A problem with the SAI is unlikely to be the cause, the combi valves are very reliable, I think I have replaced two ever.

[rickybotts_123]

Thanks again for your quick response. Is there any tests I could do or is it a case of booking it in? If so I will get it booked in so they can carry this out. It seems quite costly to just start replacing all the associated valves/hoses but I hope it's something simple.

I've got my MOT in a months time and don't want the light to pop on when there testing it. I'll keep you posted.

[Crasher]

You need to find someone with the VAG pressure testing equipment but you are more likely to find someone with something like a Smoke Pro which is very effective. To do this, the entry to the recirculation valve (the base fitting) needs to be disconnected and the boot fitting plugged and the pressure used must not exceed 0.5bar. When the engine is re-started it will smoke like it has a blown turbo and will continue to do do so long you become convinced the turbo has blown it's exhaust turbine seal, which one did one me unfortunately so it is not a test without risk.

[rickybotts_123]

The Audi specialist I have been taking it to has all the correct software etc so I will take it back to them and ask them to have a look. At least if they can pinpoint the fault I can purchase the hose/valve and fit it so I will save on some labour.

Would just be nice to have this issue sorted as its turning out to be one thing after another with this car. Thanks