Gearbox and idle acting odd in the cold

[Gambit]

As title says.

Today has been the coldest day in ages and I noticed a few odd things.

1. Gearbox slow to change down a gear when stopping at traffic lights, braking in third it shifts into 2 late and with a light thud you can feel the downshift but it's not bad.

2. With engine at running temp I started the car and while it was in park it kept trying to idle at 200rpm, this of course made it a bit lumpy, shift into drive and revs rose to 500rpm which the car is fine with.

Firstly with the gearbox issue I thought of a gb sensor but after getting the idle I'm thinking more engine related.

Any ideas?

[Martin F]

I would say it's a sensor issue which has probably been exacerbated by the cold weather.

Your idle when warm, should be around 750 - 800rpm.

Did you ever change your speed sensors?

[Gambit]

750 to 800. Is that idling in park or in drive?

on a sunny day at running temp I idle at between 500 and 600 in drive.

Which is the speed sensor?

[Martin F]

Just checked and it's actually supposed to be 650 +/- 50rpm when in neutral.

There's two speed sensors on the side of the auto-box. I seem to recall you looking at them a while back, but not sure if you ever changed them at all.

[Gambit]

No I didn't change them.

I think there is 4+ on the box and not sure which to change....

If 2 are speed sensors what are the others?


Epc shows



and




So which is it?

[Martin F]

One of them is 83181A in the second picture. I believe all the others in your first picture are lock up solenoids.

I'll see if I can find some more info\pics. My EPC is struggling at the mo.

[Gambit]

How does the speed sensor being faulty have an effect on my idle speed?

[Martin F]

Well if the ECU thinks you are moving when you're actually stationary then it will adjust timing and fuelling to what it thinks it should be, both of those could have an effect on idle speed. However in all fairness these type of sensors usually fail the other way in that they give a weak signal when you are actually moving.

Likewise the speed signal is used to adjust when the autobox changes up and down gears, so if it's not correct then the gear change issues you mentioned could occur.

It's a theory that really needs to be validated by checking the speed sensor signals with an oscilloscope or similar. However if the sensors are relatively cheap, then it could be eliminated by just changing them.

[Gambit]

Also, adding to my never ending list of things that bug me...


Sometimes whenI drive the car cold it has a... hole in the throttle...

eg. if you feather the throttle at say, pulling onto a roundabout (cutting into traffic you can get a jolting sensation if you have the pedal at the exact point.
Also if you lift off suddenly you get a jolt, bit like ropeing your car to a dump truck and driving away, when the rope goes tought, that kind of jolt.?????

[Martin F]

I've just re-read your old thread here http://www.mkivsupraownersclub.com/f...ad.php?t=13390

and I think I would definitely be looking at the speed sensor signals.

As well as the actual sensors there is the possibility that the speed signal is not finding it's way to the ECU correctly. The signal goes through the odometer (for obvious reasons) and these have been known to be prone to dry joints.

It may be worth speaking to Pete at Thor and asking him purely for a price to check the speed sensor signals, both at the sensor and the ECU.