Audi A3 SE 1998 91000miles - Car idles high and cuts out

Are you getting any codes (Dash lights)?
Could be any number of sensors. Hopefully the codes will help narrow down the high idle.

The stalling could be a dirty fuel filter. Has it ever been changed? It also would explain NB 3.

Good luck and let us know. :)

Thanks for the reply!

I am not getting any dash codes (none of the warning lights are lighting up).

I am not aware of having a fuel filter replaced.

I took the car to two garages:

Garage 1 said it was the lambda sensor and possibly the air flow meter.

Garage 2 said it was the throttle needed replacing.

I drove 100 miles yesterday and it was fine after. It seems the car is most prone to cutting out when it is just warming up, but that could just be a coincidence so far.

Does that info above help?

Thanks,

Chris

I would try the least expensive options first. Replace the fuel filter, clean the air flow meter, and clean the throttle.

The lambda or O2 sensor has more to do with a fully warmed up engine.

Good luck and let us know.

Would these things be done as part of a standard service?

If I get the symptoms while the car is warming up does that mean the lambda and O2 sensors are not at fault?

One of the garages told me that cleaning the throttle would cost £60 however it may cause permanent damage to the car if I drive it afterwards. What is your opinion on that?

Thanks, Chris.

Hello,

Thanks for looking at this. I just have a few other quetsions which may help:

If a computer were hooked up to the car and it was the lambda sensor or airflow meter or throttle or fuel fillter would it pick those up?

Or is this a case of "here are the symptoms and the corresponding diagnosis for this". I.e. There is no possible way of narrowing down without trying something and seeing whether that fixes it?

Or can I provide any more detail on the symptoms which may help home in on the actual problem? I.e. the symptoms when it is lambda sensor is *not exactly* the same as the symptoms when the fuel filter is playing up. In which case what info would you need?

Thanks a lot in advance,

Chris

[b:0643cab248]After rereading your post I did not address the 2,000 rpm idle. That can be caused by a vacuum leak. Check all your vacuum lines for proper connection, brittle cracks, and soft and gummy leaks. Look closely at the PVC valve and the power booster for leaks from their hoses and connections. They require a lot of vacuum. Vacuum leaks can also cause the intermittent stalling.[/b:0643cab248]

Changing the fuel filter should be a standard service item done at presribed intervals. Difficult to test for a clogged filter short of removing it and measuring the flow rate thru it. It is cheaper to simply replace.

The O2 or lamda sensors is considered a maintenence item that should be replaced around 100,000 miles. It definitely can be tested. Most better OBDII scanners and the dealer test equipment will be able to monitor it's function and determine it's status. The lamda has to reach at least 600F degrees to function properly. This should only takes minutes.

The air flow meter can be tested but the results are normally a "pass or fail". Testing would not indicate if a cleaning would help.

Their is a throttle position sensor on the throttle body that can be tested. Again it is a "pass or fail". The test will not determine if a cleaning will help. Some throttle bodies come with a special coating to prevent buildup. The manufacturer recommends that they not be cleaned. Check your service manual or the manufacturer to be sure. Cleaning would remove the coating and necessitate more cleanings.

A hookup to a computer will monitor the functions of all engine controll devices and be able to pinpoint any that are not operating correctly. There are several not even mentioned that can cause the symptoms you have described. If you find no vacuum leaks and the fuel filter replacement and cleanings don't help then I would have the computer diagnostic done.

Sorry for the long post but hope this helps. :) Let us know.

Thanks a lot!

I notice that the car seems to have most problems when it is cold/just warming up. Once its warm its not so bad. Recently it has been having the problems more frequently. I've been experiencing more juddering when in low revs in say gear 2/3.

I just wanted to better undestand what a PVC valve is and power booster?

I understand vacuum lines in layman terms are the tubes that connect bits of the car.

PVC could be PCV? Something which stops rubbish in the oil going into the engine?

Power booster?

Thanks again,

Chris

My bad. :oops:
PCV = positive crankcase ventilation. It uses engine vacuum to perform it's function.

Power booster = brake booster It is a large metal canister that has the brake master cylinder attached to it. It's function is to require less foot pressure on the brake pedal to stop the car. It also uses vacuum to perform it's function.

A vacuum leak is air entering the engine that is not metered. It will normally cause a high idle. It will also confuse the computer as to the proper amount of fuel to add for the engine to run properly.

Good l;uck. :?: Where are you located?

I'm located in London.

Thanks for the link. Seems fairly easy to understand. One thing I noted "Vacuum siphons fuel through the idle, main metering and power circuits" however I thought vacuum was more to push/pull air around the system?

[quote:df00f9a7ff="christhedon"]I'm located in London.

Thanks for the link. Seems fairly easy to understand. One thing I noted "Vacuum siphons fuel through the idle, main metering and power circuits" however I thought vacuum was more to push/pull air around the system?[/quote:df00f9a7ff]

Know a good garage in Burnham-On-Sea. Dereck is a very knowledgeable technician. Might be a bit far for you tho.

The reference to "siphons fuel" is meant for engines without fuel injection and with carburetors.

8)

Well here is an update on the situation... I was told by a garage that the throttle body needed cleaning before putting any computer diagnostics on the car. Once the throttle body was cleaned they said the air mass metre needed replacing and replaced it. Then they said the car was fine. Now the car has the same symptoms however when I get the high idle problem, it is nearer to 3500 rpm than 2000. The other two symptoms still exist. They now say the problem is a faulty ECU.

What do you guys think of the above diagnosis/steps taken?

What do you think I should do next?

(One thing I've also noted with the car is that the temperature gauge when I'm driving hangs around 75 degrees whereas previously it would hang aroung 90 degrees.) Could this be related?

Appreciate your help. Thanks, Chris.

Hi,

Sorry to bump this, but do you have any ideas? Is the temperature gauge not going up an indication?

Thanks,

Chris

Does anyone have any further thoughts? I'm worried about replacing the ECU and still having the problem. Could I get the ECU reprogrammed instead?

Thanks in advance,

Chris