Mechanics

CAR STARTS AND IDLES REALLY LOW, SOMETIMES STALLS. WHEN WARM IT IDLES AT JUST UNDER 1000 AS NORMAL.

1998 Audi 100 • 100,000 miles

I recently had to recharge my battery which I removed from the car first. Car seems to drive fine after its warm but when the clutch is used when cold it will stall
Avatar
Galva
October 5, 2012.



What engine is in your car?

If this all happened after you replaced the battery, it could be
that the ECM lost its "Learned Throttle Adaptation".

Over time, the throttle bore in the engine gets dirty and the ECM
has to move the throttle more open, to maintain the specified rpm, because
the dirt is restricting air flow.

This re-learn (after a battery disconnect) can take a few minutes
or a few days before things are back to normal.

The best thing to do is to clean the throttle bore and then to use
a scan tool such as VCDS to perform a Throttle Body Adaptation / Alignment.

Such as I am doing here on a 1.8T VW engine:

http://www.youtube.com/watch?v=OAfeBLENkfA

If that did not solve anything, check for stored fault codes, vacuum leaks
and any other engine tune components.

Thomas

Tiny
Exovcds
Oct 5, 2012.
Thanks for the quick reply. The car is a 1.8 cabriolet. I have cleaned the throttle body but do not know about the adaption or alignment via scan tool. I have a basic OBD2 scanner but have been unable to locate the port on the car. I dont know if it is the old type. Is it possible it could be the engine coolent sensor or the pvc valve. Thanks for your help

Tiny
Galva
Oct 5, 2012.
Incorrect temperature input can cause idle issues... if your OBD2
scanner can read sensor values, you can monitor that.

Here are some common DLC locations:

http://www.ross-tech.com/vag-com/cars/dlc.html

It could be in the center console before or after the hand brake.

Thomas

Tiny
Exovcds
Oct 5, 2012.
I forgot to ask what type of fuel injection system your 1.8 uses.

Sounds like a Euro model. Does it have a motorized throttle body?

If not, then the throttle adaptation does not apply.

Thomas

Tiny
Exovcds
Oct 5, 2012.
Hi when I cleaned the throttle body it has a motor underneath that controls the butterly valve. This must still work if it idles when warm, is this right? Does it having a motor mean that the ECU may correct the fault in time.

Tiny
Galva
Oct 5, 2012.
Sorry about the late reply... had to run an errand.

If it is motorized, then yes, the ECM/ECU should be able to re-adapt
to an idle that will be normal... IF the cause of the Idle is due
to a throttle alignment / position issue.

Usually after cleaning & before adapting the ECM, the idle will be
too high (this is with the battery always connected).

When battery is disconnected or the voltage is too low during
start-up, then the idle can start to misbehave.

A sample of a motorized throttle body in action...

http://www.youtube.com/watch?v=pzKD0lu6iqs&feature=plcp

...the part that moves on its own is the throttle being moved by
the ECM to maintain correct idle.

If the problem persist for too long, then you will have to see if
an adaptation via scan tool will solve your issue.

If the alignment does not cure the issue, then you will need to
check for other causes.

Thomas

Tiny
Exovcds
Oct 5, 2012.
Sounds liek the Idle air control valve needs replacement.

Are you talking about the Throttle Body?

Tiny
Exovcds
Oct 6, 2012.
Yes, I believe, now looking at the entire conversation as for some reason it was not showing previously, what was referred to as the "learned throttle adapter" may be the same thing as a throttle position sensor and could be the problem. They do have to be calibrated after installation. I calibrate them with a multi-meter, but if there is an ECM program to have them learn their position then follow that.
The idle air control valve works like a, "choke" and keeps the idle steady depending on; whether the engine is warmed up or not
engine load
trhottle position and accessory load

So, they do go hand in hand a bit. One can go bad and affect the other. But if your problem gets better with temperature I would say its the IACV. If you want to check it you can remove it and keep it connected, then turn to key to the run or start position the see if the plunget moves. The plunger opens and closes ports on either side of the butterfly valve of the throttle body to keep the idle steady. So, if you replace make sure they are clean by spraying brake cleaner from the outside in towards the iner throttle body. The keeps deposits from going farther in towards the IACV and pushes them into the throttle body bore where they can be removed. Then I would run a can or two of BG44K, which you can only find at car dealerships, as it is the best fuel system cleaner on the market. In fact plan to change your oil after using it, it may also affect performance as it cleans out gunk. But it will all straighten out for the better, as the deposits all end up in your motor oil if the don't get blown out the exhaust.

Hi in reply to the last thread, first of all thanks for all the help. I would like to check the iacv. It sounds like you are saying this is in the throttle body housing? I've checked the intake to the tb and theres no electric connections. Could you help me locate the iacv so I can check and clean it. Occasionally on start up instead of dying it revs itself from 1000 rpm to 1500 rpm over and over. Is this another symptom?

Tiny
Galva
Oct 12, 2012.
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