Re: 1994 MB 300 idle surges when cold
- From: Jens <jens@xxxxxxxxx>
- Date: Tue, 20 Jan 2009 02:01:11 -0800 (PST)
On Jan 14, 4:33 am, "Sam Anselmo" <j...@xxxxxxx> wrote:
It will start fine, but with no accelerator input the engine will run up to
over 1000, you will hear a solenoid or switch kick in, the rpm will cut,
sometimes stalling the engine, sometimes not, then the rpm will run up again
and this will go on and on only while cold. Once running a few minutes,
everthing is fine. Any ideas? TIA
A take it is the 104 engine.
There is really not anything switching on/off, except the air pump
swiching off after a minute or so depending on the temperature.
Until the oxygen sensor warms up, the engine will run in open loop
mode (without feedback from oxygen sensor). I open loop the mixture is
controlled by inputs from throttle position sensor and temperature
sensors. And in idle the throttle is controlled by ECU.
So something is disturbing the control. It could be the throtte
position sensor (potentiometer), the temperature sensors or a vacuum
leak (intake manifold and vacuum lines).
Since it works in closed loop, I would suspect a small vacuum leak
(the ECU is still able to correct the mixture according to the oxygen
sensor feedback).
.
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