Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Revs not going to idle

You can do an adaptive map reset simply by disconnecting the battery. No Protune required.

In a previous post about this subject, I explained what I did to find the culprit of this strange problem; Swapped and cleaned the Idle Air Control valve with the one on our other M3W. New throttle cable. Greasing the throttle pedal and disconnecting the battery. I swapped the Oxygen sensors with our other M3W. All no result.

The last what I could think of was the ECU.
So today, I swapped the ECUs of the cars, but also this didn't solve the problem.
So, where to look next?

To make the whole problem even weirder, this is what I experienced during my test drives:
The idle remains for about 3 seconds at around 2400 RPM when coming to a stop. When at a standstill, it drops to normal idle. When the car is rolling and putting the gear in neutral, the idle remains at 2400 as long the car is rolling; when it comes to a stop, the idle drops to normal after 3 seconds.
I even did this rolling downhill for +/- 2 kilometers, and all the time, it remained 2400 steady till to a stop.
Then I drove UPHILL. Stopped. Idle was for 3 seconds 2400 and dropped to normal. Released the brake and the car rolled BACKWARDS during this; the idle went up by itself to 2400 RPM! I didn't touch anything! Only let the car roll backwards.
I did that several times and every time same result.
To make it completely weird, some moments it is all normal again! Even when rolling and putting the gear in neutral, the idle goes directly back to 1000. I did it several times in a row. All normal. And suddenly, the same weird idling problem started again.
This above behavior happened with both ECU's.
So where to search next ?? Any suggestions ??

The symptoms are very confusing, try disconnecting the speed sensor down by the front wheel and see if that makes any difference as that can be the only way the ecu is detecting the car is moving. Why that should effect the idle I don’t know.

Thanks for the info. And Ian, thanks for the launch across the room reference when not installed. That could save a lot of grief and the neighbors hearing very coarse language uttering from my shop.

I think I've read somewhere on here that it's a good idea to replace the TPS screws with something easier to work with. Anyone know the thread size & length of the screws?

I agree with Roger it's almost certain to be something to do with the front wheel speed sensor.

A couple of other things you could try to confirm this:

When you swapped the ECUs over did you try both cars to make sure the fault had not transferred or just checked the fault was still on the original car?

Try reloading the ECU map, either with a saved copy if you have one or simply copy the map from the good car.

This extract is from an S&S manual, https://www.sscycle.com/docs/defaul...50fuelinjected-4-1-8in-bore.pdf?sfvrsn=2 different engine but I am sure the same applies to the M3W:

"Vehicle Speed Sensor (VSS) and Speedometer
A properly connected and calibrated vehicle speed input is important for proper engine operation as the ECM uses the vehicle speed input for idle control and engine history data. It is recommend a H-D(R) #74430-00A or equivalent vehicle speed sensor be used. This sensor is compatible with most after market speedometers. The speed input into the ECM can come directly from this sensor, in parallel to the speedometer, or from an output signal from the speedometer."

Since 2013 the operation of the speedometer has been on average 5 years and I have never seen a different engine operation except for the indicators.

Had this on an early Superdry - idle sat at 2000 when off pedal but would immediately fall to normal when coming to a standstill - changed every sensor including wheel speed sensor - still fault persisted - last resort changed ECU and fault disappeared and has now been fine for 2000+ miles.
I advised Laurens to change the ECU - which he has but still fault persists so perhaps in this case the wheel speed sensor is faulty although I can't see how as the car idles fine when started and at all other times??

It has been suggested simply remaking the electrical connections could restore a function.
I wonder if by replacing the ECU the fault was fixed by remaking the joint , rather than by replacing a faulty ECU?

I have long been concerned about the unsuitability ( i.e. lack of waterproofing ) of most of the electrical connectors, given their positioning etc.
Same applies to these sensors.