Petrol A4 B5 1.8 Lumpy Idle

[amatty]

For a few months now my car has had a lumpy idle which shakes the car around a little, but the basic speed is a quite steady 900 rpm with some engine vibration.

The car has just passed the emissions check for its MOT to my surprise and still gives 33mpg on general running around

Have cleaned the throttle valve with a bottle brush and brake cleaner after removing the tube behind the scuttle which goes to the air mass meter.
This seemed to help a bit but have also changed plugs, air filter, and temperature sensor, disconnected battery to reset computer and gone through various proceedures to re initialise the computer. Have also checked for air leaks by squirting WD40 and brake cleaner over the inlet manifold and throttle valve area to see if the idle changed as the fluids were sucked in - but nothing changed.

The engine runs just the same now so think the problem is probably the throttle valve/idle control valve. Can get another for £35 from a local breaker but have not found out how to remove mine from the inlet manifold. Could it be the sensor on the camshaft even though a check with a plug in computer says it is OK. However the computer did say the the idle valve is at one end of its travel - but is this cause or effect ?

Two of the four screws which attach the throttle valve to the manifold are masked by the big plastic tube which connects to the mass meter tube which runs behind the scuttle - I thought this would be easy to remove to gain access to the allen headed screws but find that this tube has another one underneath connected to the breather and that this can only be remove by undoing a very difficult to reach jubilee type clip underneath.

What is the best way to remove the throttle valve assembly please without taking half the car to pieces?

Even better does anyone have any other ideas on what is causing my "lumpy" idle.

Matty

[amatty]

I have unfortunately not had any replies to my problem so far, but in the meantime I have had a second hand throttle body/idle valve fitted complete with a new set of breather pipes - the old ones just fell to pieces when taken off. A very competant local Audi mechanic had computer checked the car a while back and it said the idle control valve had caused an error report. We guessed this might be the problem and therefore I asked him to change the throttle valve. At 78 I am now finding such jobs rather bad for the back if I do them myself.

I am afraid the car still runs rough on tickover in exactly the same way, BUT the error report has gone and the the computer says that there are no problems.

So with plugs changed, throttle valve changed, temperature sensor changed, etc. where do I go from here - above 1000 rpm the car runs perfectly it passes the emissions tests with flying colours and has excellent fuel consumption.

Some of the most brilliant engineers in the country are working on the problem, but we haven't found the answer yet !!!!

Somebody must have found an answer to this problem which does not seem to be uncommon - -HELP PLEASE

Matty

[N19]

I don't know that much but can the throttle be realigned, what's the engine code

[amatty]

Hi
I am informed by the local AUDI agent that my A4 b5 is an early model and does not need the ECU to be re aligned , I have however been through various procedures eg disconnecting the battery for a time, switching on the ignition for a few minutes, putting the throttle in various positions etc. But in each case after running badly for a few miles the system gradually resets itself to its original 900 rpm slightly lumpy tick over.

I have come to the conclusion that most of these procedures are based on black magic and not science though for later models a computer may be necessary to reset the ECU parameters.

Matty

[N19]

Hi Matty,
I've been looking after 2 A4 B5 (97 AEB & 2000 APU) 1.8t both turbo'd for years and as far as I'm aware they both can have the throttle aligned 1 is cable and the other is drive by wire which I did this to today and it settled the idle. are the revs hunting sort of, I've been searching around for a throttle body without wires going to it, but if Audi say it can't be done then I don't know what to say. when ever I've read about the idle on audi's others always mention the alignment,
best of luck with it

[acmo]

Yes you can, but under certain circumstances.
Throttle Body Alignment (TBA) - Ross-Tech Wiki

[acmo]

Usually a lumpy idle will be a split vacuum hose some where, just check all the little vac pipes running to and from manifold etc

[green A8]

Usually a lumpy idle will be a split vacuum hose some where, just check all the little vac pipes running to and from manifold etc

I agree with the above, also be aware that they can collapse internally and give no visable clue to their failure. I spent ages hunting down a split vac hose with no success, in a fit of angst I simply replaced vac every hose I could find in the engine bay. Result, even idle all of a sudden, and one delighted Audi owner. I later discovered that two hoses had both collapsed internally. If in doubt replace the lot! A very cheap and painless fix.

[amatty]

Thanks to all for your interest - my car is not a turbo - just plain 1998 petrol 4 cylinder 1.8 with a cable throttle. It seems that most A4s in America are turbos, which apart from other problems clog up their oil filters in the sump if not properly maintained.
As you can see from my previous inputs I have already carried out extensive checks for split hoses by inspection and spraying the possibly leaking areas with both WD40 and carb cleaner to see if this makes the running engine any different by sucking in the gases - it had no effect.
Since doing these checks and now that the throttle body has been changed, a computer reported fault with the idle control valve there has gone. When the throttle body was changed, all the breather area hoses broke up and had to be renewed - they were quite expensive because we could only get them from a Main Audi dealer. So I am pretty sure there are no air leaks in this area.

The idle is still lumpy, has always settled fairly steadily at 900rpm, but is perhaps a little improved, with the better throttle body - so maybe - despite the view of the local dealer, computer throttle alignment may be the solution after all.

One day I'll find the answer thanks- but will have to find somebody with a suitable computer who can realign the throttle body as advised by ACMO above - my local Audi Man only has a very simple diagnostic machine.

Thanks again.

Matty

[Crasher]

Hello Matty, what year and engine type code is your Passat?