Motronic ECU reset

[BristolE30]

Hey zone

Wondering if anyone has any understanding of what happens when the ECU on our cars is reset. I know it goes into a learning mode, but what is actually happening with the maps and data?

Context to the question is that I’ve always had a lumpy idle/misfire/issue once my engine has ‘learned’. I’ll kick the throttle and it’ll gag a bit and also want to stall, but it just about saves itself.

If I reset the ECU (disconnect battery) it’s like the engine never had an issue. It drives amazingly and doesn’t stall or bog for at least a day.

So I want to know what’s happening during the learning process after disconnecting to see if it can help me track down my issue. Wondering if anyone has knowledge of the maps or process?

[BenHar]

Check the throttle position switch is set correctly.

Ben

[Brianmoooore]

There's no feedback loop to a Motronic ECU with no lambda sensor, except the engine revs for idle speed setting, so that's the only thing it can possibly 'learn'.

[paultv]

Mines the same...after a period off the battery power the idle is faster...some kind of default map...but then it settles down to 750 rpm but rougher some how.

paul

[BristolE30]

Check the throttle position switch is set correctly.

Ben

Will double check it, but what makes you say that? I went through a whole process (and huge thread) on trying to solve it, changing out ECU’s smoke tests etc and never got to the bottom of it

[BristolE30]

Mines the same...after a period off the battery power the idle is faster...some kind of default map...but then it settles down to 750 rpm but rougher some how.

paul

Mmm interesting, so it’s like the ECU just increases the rpm after a disconnect. If there is no feedback loop as Brian says maybe our issues lies with the idle being too low. Could be a throttle body/stop issue I guess..

Feel like I’ve tried it all...

[BristolE30]

There's no feedback loop to a Motronic ECU with no lambda sensor, except the engine revs for idle speed setting, so that's the only thing it can possibly 'learn'.

Any theories for my phenomena then?

[Brianmoooore]

Check the throttle position switch is set correctly.

Ben

Will double check it, but what makes you say that? I went through a whole process (and huge thread) on trying to solve it, changing out ECU’s smoke tests etc and never got to the bottom of it

If the idle section of the TPS doesn't switch closed circuit when the throttle closes, the engine won't be running on the idle map.