cured poor idle

[bigengines]

Hi all, just wanted to let everyone know that i had problems with the idle speed on my A4 2.4 v6 petrol 1998, it was surging up and down between 700 and 1000 rpm so i took it to a local independent audi specialist who checked it out and said there was a fault on the engine temp sender and also showed a fault on the throttle body, after the replacement of the temp sender the surging has stopped but every time i approached a junction the rpm dropped and car wanted to stall, it never actually did stall but was very close to it, so i removed the throttle body ( which was not an easy task ) and found it to be full of oily carbon deposits around the throttle flap, i used carb cleaner and spent 10 minutes cleaning the inside of the throttle housing so it was immaculate.
I then refitted the housing and road tested the car, all i can say is what a difference, by just doing this it has completely cured the poor idle fault and now when i stop at a junction the rpm drops to 900rpm and stays there without hesitation, so i just thought i would pass on this info as it might help others with a similar problem, i would definately recommend cleaning the throttle body as a matter of course for any idle problems as it may well help.
thanks for reading, bigengines.

[dpnewbold]

Hi
Thanks for your post. very informative. I too have the same problems you mention. Just replaced the mass airflow meter and it has improved immensly, however I still have the idleing as you had.
Is it difficult to remove the throttle body ?? Any more info on how to remove and clean would be good.

Cheers

dave

[bigengines]

HI Dave,
To remove the throttle body i first had to remove the black plastic cover over the engine then at the rear of the engine there is a plate with some connectors and small pipes on the top, this plate sits over the top of the the throttle body, i removed the 3 x 10mm bolts and a small vacuum pipe and the electrical connector plugs, the plate then swung out of the way but you cant remove it completely because of more pipes but it was enough to get access. I then removed the big pipe which goes from the plastic housing on the throttle body to the mass air flow meter, then i removed the plastic housing which sits over the end of the throttle body, this is held on with 1 x 5mm allen bolt, but there is the engine breather pipe that plugs into the plastic housing and to remove that you have to pinch the clip together and give it a pull its a bit fiddly but it must be done, after the plastic housing is removed you can then get access to a rubber pipe on the top of the housing to the air filter box, just remove the pipe from the top of the body (mine was held on with a jubilee clip) and push it out of the way, then you can remove the 4 allen headed bolts which hold the throttle body onto the manifold, there are 3 x 5mm allen bolts and either 1 x 7 or 8 mm allen bolt, these bolts are really fiddly and you cant see them unless you use a mirror which i did, once these bolts are removed the throttle body comes away from the manifold, you will then have a bit of manouvering room to release the throttle cable and the electrical connector plug which goes onto the side of the throttle body motor, once these are gone the body should lift out and you can start cleaning, as i said its really fiddly but if you are patient it will be ok, after cleaning everything goes back in reverse order, take care not to damage the red 'o' ring between the throttle body and the manifold when your refitting the body, and there was an earth wire that went onto one of the bottom body bolts as well make sure it goes back on, i used allen sockets and a ratchet to remove all the housing bolts as i think using allen keys would make the job more difficult simply because access is tight down the back of the engine. If your going to attempt to remove the throttle body after reading this and you need any more info just let me know. I hope this discription is ok for you, it would probably make more sense while actually doing the job, it might sound daunting and it is fiddly but i would definately persivere as its not as bad as it sounds and i am sure it would make a big difference if you do it.
Happy fiddling Bigengines

[dpnewbold]

Hi
Wow...many thanks for such a wonderfully detailed and lengthy reply. I have printed it out so I can refer to it. I need a clear weekend and a bit of warmer weather first though.

I only bought the audi last week and almost immediately it started running like a bag of farts but replacing the mass air flow meter has helped 100%. She's now running very well but there is still that slight idle-ing problem. Hopefully cleaning out the carbon deposits in the throttle body will help.

My MPG is a bit disappointing though....only about 24 around town. But I don't suppose a (heavy German) 1.8 automatic is ever going to get much more than that. Used to get about 29-31 out of my auto 1.8 Avensis and 40 plus on a run, but Toyota's are lighter cars. The Audi feels like its carved out of granite !!


Once again thanks for the trouble of writing in so much detail.
I'll let you know how I get on.

Regards

Dave

[labarnes]

I echo that response. This is just what I'm looking for and has given me the confidence I needed.

I was out in the cold and rain today, stripping down the Airflow Meter and cleaning the breather pipes. I have to say that they looked quite clean anyway and I still get the idle problem (EXACTLY as you described here - must be a common fault huh?).

Anyway, my next step was to remove and strip the Throttle Body. I've read a few posts that say this is the thing to do, but it looks quite complex and the Haynes manual has scared me; Page 4A-6, section 4.14 says "note that when the voltage supply to the unit is interrupted, the throttle value moves into a mechanically set basic position. After refitting the unit the basic setting procedure must be carried out by an Audi/VAG dealer using the test instrument VAG 1551 or 1552. 15 Do not attempt to open the multiple housing."

However, I will follow your guide and see how I get on. How did you reset the basic position? I think this is refering to the Throttle Value Potentiometer. Is that the same as the throttle body??

Thanks!

- Lee

[bigengines]

Hi labarnes, just a quick note that my vehicle has a V6 engine and the procedure i described to remove the throttle body will be unique to this engine, i would think that to do the same job on the other audi engines should actually be easier as there should be more room around the engine.
After i refitted the throttle body i just left the ignition on for 20 seconds then started it up so i asume the throttle values have remained the same or they have auto updated if you like, but i have not had to reset anything with vag-com, all i can say is i would definately get the throttle body cleaned out as a matter of course as something a simple as this may help with your idle fault, and even if you have to get yours reset by an independent garage who has vag-com i am sure it will be worth it, if you do clean your throttle body could you let us all know how you get on,thanks.
Bigengines.

[karenville]

Thanks for the great write up Bigengines, I cleaned the throttle body on my wifes 1998 A4 which seemed to cure the stalling/idling problem for a week. I've just cleaned the mass air flow meter but still seems a bit rough at idle. got any ideas?

[labarnes]

Hi Bigengines.

I've taken the throttle body off. Wehay! It did have the water pipes connected, so I had to remove those as well. Someone had definitely tried doing this before, as some of the pipes had jubilee instead of compression clips, but they had assembled the breather (?? Big pipe between the TB and the Airflow Meter??) incorrectly and the rubber gater was all screwed up meaning that air could escape. The TB and this breather pipe were absolutely smothered with oil and I noticed a few splits and perishes in some of the smaller pipes. That certainly goes a long way to explaining the terrible idle...

I'm going to order replacement gasket and pipes from Main Dealer tomorrow morning. In the mean time I bought some Carborettor cleaning spray and gave the TB a thorough cleanse. Looks brand new inside!

I'll be re-assembling the TB on Saturday. Can't wait and I know about the 45 second TB adapt trick as well. Hopefully with my clean parts, new parts and a new Coolant Temp Sender my car will idle like new...

I'll let you all know how I get on. Thanks again. Lee

[bigengines]

Hi all,
I am glad that my piece of info has helped a few of you guys, with regards to the cleaning of the mass air flow meter ( maf ), i believe how they work is that there is a very thin wire that is open to the air flow that goes through the maf, this wire gets hot under normal running conditions and produces a resistance value which is acted upon by the engine control unit (ecu), so if you open the throttle you get more air and at a faster speed passing over the hot wire in the maf this then alters the resistence output from the wire by cooling the wire down so depending on how hot or cold the wire becomes the ecu works on this value and dictates what fuel should be put into your engine, it is slightly more complex than this but i am trying to keep it simple, now i dont think its a good idea to be cleaning the maf at all as you will probably do more harm than good because these things are quite fragile and if you have already had the maf to bits you will have seen how thin the wire is so if you spray something on the wire to clean it then there is a possibility that a residue or film from the solvent used could have coated the wire and altered its resistence value which will then give the ecu the wrong signal and then ultimately you will have the wrong air / fuel mixture going into your engine resulting in poor performance, poor idle and poor fuel economy etc. So if you have cleaned the maf and the throttle body and your still having problems then it could be that your maf has had it, but i would get the vehicle onto the vag-com and get it checked out as it would be cheaper in the long run than just changing sensors without knowing for certain which one is at fault, i hope this has helped explain a bit more of how these things work and given you guys a bit more of an understanding and if you do find you have a faulty maf then get a genuine one because your asking for more trouble if you buy an aftermarket one cos there crap. Thanks for reading.
Bigengines...

[labarnes]

Hi bigengines

I really do want to thank you for your thread. I finally got around to re-fitting the TB after removing it and giving it a thorough clean and it idles perfectly now. I'm even noticing a slight improvement in acceleration < 3500 rpm and a massive improvement > 3500 rpm (it's like having a turbo).

I replaced 2x 15mm pipes, one fuel breather pipe, one TB gasket and the Coolant Temp sended. £58 from a main dealer in total and it took me about 4 hours I guess in total...

Very Very delighted

Thanks very much for your advice and thread.

- Lee