reset ECU with odd results.

[thetroublemaker]

As a lot of you will have seen i have had issues with my cars running.

Yesterday the codes were read - with it coming up "NO DTC SET"

Today in other work the battery was removed, and when i picked it up i assume it had reset.

And the car runs like a dream.

Any thoughts on why this is? I would have assumed it would run worst when reset?

[Paullyp]

It is likely that when you reset the ECU, it canceled any minor fault codes and the "limp home" mode, people forget that 3 minor fault codes will "fool" your car into limp home mode and the result is you take it to your nearest dealer who will reset the codes/ or place the ECU into learn mode,P.

[thetroublemaker]

surely though limp home would have put the ECU light on?

[Paullyp]

not all the time, some faults will not produce a code, relays, fuse failure etc etc,P.

[thetroublemaker]

OK.

Well its gone back to running bad already.

What i have noticed is that the car, when cold has a "surge-hesitate-surge" behaviour, about 1hz in frequency at a steady throttle.

Now this dosent make a great deal of sense, as while this is what i would assume would tie in with a lambda fail, the lambda should not be talking to the ECU when the car is cold.

Its all weird

[Paullyp]

Pure Volvojoy