400SE Road Speed Sensor

[Hoopy400]

I have a 400SE which idles too fast. Its fine on first start up, stepper motor does its stuff dropping down the revs in stages, and it settles down to sub 1000 rpm. However, once driven it will not drop to less than about 2000 rpm even when I come to a complete stop. I understand that there is a road speed sensor that tells the ECU whether the car is moving (>3mph) and this controls the idle speed but I cannot find a reference to it in the wedge manual. Can someone point me in the direction of where the sensor is located in the car, what it looks like and any tests / checks I can perform to see if it is working correctly. Thanks, Steve.

[blaineuk]

If it’s a hot wire 400, it is on the inner wing near the brake master cylinder, has a speedo cable on either side of it.

[Hoopy400]

that is great thanks - I'll check it out

[Boxhiller]

Hi Hoopy,
So what was the cause of this? Was it to do with the road speed sensor?
I remember mine (Hot Wire) did the same on an intermittent basis before I took it off the road.
I de-sooted the inside of the stepper motor and it seemed to work for a short while but the problem returned on and off and I didn't get around to fixing it.

[Hoopy400]

Unfortunately still not sorted. Road speed sensor and stepper motor both work fine. Tried various things but none worked. Car off the road now for the winter but will probably have to take her to my local TVR specialist to get it sorted as it annoys me sitting at traffic lights etc with the engine running at 2000rpm. Will let you know if I resolve the issue.

[nwarner]

Maybe you could have an air leak somewhere?

Nige

[Boxhiller]

Hoopy400 said:

Unfortunately still not sorted. Road speed sensor and stepper motor both work fine. Tried various things but none worked. Car off the road now for the winter but will probably have to take her to my local TVR specialist to get it sorted as it annoys me sitting at traffic lights etc with the engine running at 2000rpm. Will let you know if I resolve the issue.

OK thanks. Will be good to know what the TVR specialist - or anyone else - has to say.

[Boxhiller]

nwarner said:

Maybe you could have an air leak somewhere?

Nige

Yeah I thought that but with a constant air leak I suppose it wouldn't come down to a regular idle speed once warmed up from cold.

Anyone else got a view?

[blaineuk]

Sounds like the stepper motor is at fault, do you know anyone you could borrow a known working one from?