1800 RPM idle problem.

[skerd]

I have a 1995 S4s that idles at 1800 RPM after
it is fully warmed up. If I turn the engine off and
turn it right back on again, it will idle OK. The dealer
replaced the idle compensator valve and reset the
idle. That fixed it for a few weeks but the problem is
back again. Everything checks out OK. Also when the
car is overnight cold and started the idle is only
around 950 RPM. It is either too low or too high.
Any suggestions what it could be?

Thanks.

[adrianmugridge]

Have you tried resetting the ECU ? It 'learns' things ( temperature inputs, fueling, air intake etc )and sometimes gets a bit confused. If you reset it, it then relearns and tends to run better.
To reset it, just pull the ECU fuses for a few minutes and disconnect the battery. Give it a try.

Adrian Mugridge
[e-mail]
www.adrianmugridge.co.uk

[Skerd]

Thanks for the tip.

I will try it, but can I ask you two questions to be sure.
You said pull the fuses (plural). I looked in the owners
manual and there are two fuses. One says "ECM power,
ALDL rear" and one says " ECM & direct ignition".
They are at the right hand side of the rear luggage
compartment, on the rear face of the wheelarch.
Are these the two fuses?

Thanks.

[adrianmugridge]

Yes, they are the ones. I don't know if only pulling one works, so I always remove both. Many owners notice a difference in driving ( for the better ).

Tell me if it works !

Adrian

[Skerd]

Adrian:

I was too busy today to remove the fuses but I
did think of one more thing. To fix a previous
engine stalling problem I had the ECM mem cal
reprogrammed with an updated version. Will I
lose this update by removing the fuses/disconnecting
the battery?

Thanks.

[adrianmugridge]

Skerd

No need to worry about that. The code for the Memcal is stored in a chip called an EEPROM ( Electricaly Erasable Programmable Read Only Memory ). A special programmer is needed to alter the contents of the chip - fear not, it's impossible to lose the contents by removing power ( unlike a PC for example ).

Adrian

[Skerd]

Adrian:

Thanks again for your quick answer. As soon
as I get a chance (busy tax season) I will try
your recommendations.

[Skerd]

Adrian

Just wanted to let you know I pulled the two
fuses for the ECM. Unfortunately it did not help
the high idle. I guess the AIC has gone again
because it has been a few months, not weeks since
it was repaired. No big deal. Thanks for your help.

[Skerd]

Wonderman

I will have the TPS looked at on my next
visit to the dealer. Thanks.