ECU reset

[Rhyse30]

I'm still trying to get my engine running as it should but having idling problems when cold. It's an M20B25 1989 motronic 1.3. No lambda sensor. Fuel pressure is fine. blue temp sensor reads as it should cold and warm/hot.

Every time I take the negative off the battery for a while, which I presume from what I've read resets the ECU, my idle problem goes away for the first few starts. After that it seems to just go back to the problem again.

I thought it was something to do with the throttle stop screw as this was tampered with while having an MOT. I set the screw so the throttle was open just ever so slightly more when idling, and adjusted the TPS to it shows continuity when cold and click in the right place and everything, which worked great and the car idled much better and the revs didn't drop and nearly stall the car if i pressed the accelerator quick (one of the problems I used to have).

Now after a few drives in the car it all seems to have gone back to usual even though the throttle is open slightly more.

Basically my question is is there some default setting the ECU goes to when there's something wrong and goes into like a 'safe mode' or something? I've read about cars going into 'limp home mode' or something about staying in open or closed loop....?

I know there's an underlying problem causing this and adjusting the idle will only mask whats actually going on, but why does it go back to running the same as it was before even when I've opened the throttle a bit on idle?

Even before I messed with the throttle stop screw if reset the ECU the problem would go away for 4-5 starts.

One thing I've realised is if the car stalls, when trying to start it again it struggles to fire a bit.

Sorry if something similar has been discussed before. Can anyone tell me if the ECU has some kind of safe mode or something? or suggest any thing I Should check?

Thanks!

[kam-325i]

No safe mode on these ECU's....

how dose it run if you set the throttle stop properly, IE, the butterfly completely closed and the TPS adjusted accordingly ?

[Rhyse30]

It act pretty much the same with the butterfly completely closed and TPS adjusted accordingly. I'm bit stuck about this now as anything I do to try and fix the problem, it works great for the first few times but then it reverts back to the same problems.

The engine hasn't always performed like this. It was great for a few months after I did the conversion. Then it was misfiring due to a cracked dizzy cap. but a new one fixed that. Now, I'm sure since it's had an MOT, it's been like this. It did apparently have a hole in the exhaust which was welded up for the time being. Could the hole in the exhaust cause it to fail it's MOT on emissions? Then the MOT guy might have adjusted something to make it passable?

[ethrty]

a dodgy airflow meter and throttle position sensors can cause the symptoms you describe. unfortunately the M20 DME cannot do live diagnostics to see for sure

[Rhyse30]

Can this be fixed by adjusting the arm so it has fresh new track?

This was happening (the hesitation and nearly stalling when you press the accelerator quickly) on my old b20 engine also. Which makes my think its caused by something still on the car (something I wouldn't have changed over when doing the engine swap?).

Also, it's much worse when cold. Still occurs when warmed up just not half as bad!

The only other thing I can think of is.... I'm using the same ECU as I used on the b20 on the b25 but now with a chip. Could a fault with other areas of the ECU (not the chip) be at fault here? Sorry if I'm going of course a little, just clutching at straws really!

Thanks for the help so far!

[parkin10]

Did anyone find a resolution for this problem?