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

well, explained. Also remember as they corrode there is a smaller and smaller place of contact which leads to heat, heat leads to more expansion and contraction which leads to smaller and smaller place of contact. if this happens within a connector you will eventually toast the connector.

As suggested, I checked the earth connections from the speed sensor.
No result.

Last hope, I swapped the complete throttle body with my other M3W, including all sensors (ICV - TPS).
No result!

Does anyone know if the cables from the speed sensor first go to the speedometer and from there to the ECU? Or do they go directly to the Engine/Chassis connector and from there to the ECU?

Laurens, look at the wiring schematic in the parts handbook, if I am reading it correctly by following the colours it looks as though two of the wires from the speed sensor go to the engine chassis connector and then to the ECU, the third wire seems to be spliced together with a number of others.

It's not my style to wave the white flag, but I'm really out of options for where to look for this ongoing problem.
Besides all things I checked before (I explained in my previous posts) I took the engine loom/chassis loom connecter apart and checked and cleaned it with contact spray. I opened the ECU plug to check all wires and cleaned the contacts. I checked again all connectors involved, but it all doesn't help a damm thing.
At some moments, normal idle, but without any reason, suddenly, the high idling was there again.
To make it more strange, I was waiting for a traffic light. I was stopped with normal idle. During the wait, the engine light when on for a brief moment. Idle went from 1000 to 1200. When rolling again, the idle was back at 2500.
I did a few checks switching to neutral gear while rolling all the time with high idling symptoms; suddenly, without reason, all was normal again and remained normal for 30 kilometres. During that time I have switched about 100 times in neutral gear, but all the time, normal idling. I stopped at home with normal idling and put the car in the garage. The next day went for a ride and directly started the high idling for some kilometres, and suddenly, normal idling again for the next 20 kilometres. Suddenly high idling started again.
During the high idling, I did wobble the wires from the engine/ chassis loom and the connector from the ECU, but it doesn't make any difference.
High idling stops when the car is stopped but only goes back to 1200. When normal idling it's 1000 during rolling and during a stopped car!
To be very sure it isn't the ECU, I swapped the ECU with the one from our other car (I did that for the third time), but again intermitted high idling.
This is searching for a needle in the haystack.

It may be a bit of a long shot but try swapping the Turn Signal module (found under the ECU) between the cars. It does use the speed input to control when the indicators stay on below 10mph so could somehow be intermittently affecting the feed to the ECU and hence the idle.

Apologies if this has already been mentioned , but have you , while experiencing these symptoms , had a laptop onboard connected and running Protune to see if anything relevant is displayed ?

Just for fun I have had a passenger hold a laptop in view as I drive, to better understand the mapping screen and how it changes while driving.

In your case I am wondering if something transitory might be happening that is not recorded as an error code, but might be visible when the high idling happens ? Long shot ....
So like your own rolling road test.

Just a thought and good luck.

Another? random thought for you.
The engine temp sensor is between the two cylinders. The wiring to it is in a harsh environment. On mine i found it resting in motor with some wear on the sheathing.
If this sensor has an intermittent issue it could affect the idle? If it shows engine cold then ecu would up the revs.

Since all the obvious stuff doesnt work, panic and go improbable.

I cant remember if you have tried new intake seals, or checked inlet manifold for cracks but this has been a problematic area for a few.

Chin up, at least yours is mobile, mine has comprehensively broken the chassis in both common failure areas. Waiting for new chassis.

Friends, thanks for all the excellent advice.
I will check all the things mentioned.
@Nippy I'm sorry, but I don't have a Windows computer with Protune, and if I had, I'm not so good with computers, so I'm not sure if it would be of any help.

I've collected some courage and will start searching again to solve this problem.

I see in the parts book five ground connections at which the two looms are connected to the chassis.
I've found one under the bonnet just behind the engine. From the drawing, it looks like the speed sensor has earth on that spot.
But does anyone know where to find others?

I also see three wires in the chassis loom drawing at the speed sensor.
YB and YR both go to the engine/chassis connector.
Does anyone know where the YK go to?

YK is here, where that is actually on the M3W I don't know.
Spliced to those other wires.

Have you tried spraying penetrating oil with an extension hose near the air inlet seals on the cylinder heads when the engine is running abnormally at idle.