An idle thought

[pincher]

My car has been away for a couple of weeks having some bits done, including a new stepper motor and chip. But I still have an issue where the idle seems really high initially (as high as 2000 rpm), before dropping back down to about 1100 and then finally to it's usual 900. Seems to happen when cold or hot - and even does it if you are approaching lights etc and knock it into neutral and coast up to a halt.

Seems to take an age to drop down to 'normal' revs , even though it is probably only about 5 seconds or so. It feels almost like the choke is stuck open and sometimes it feels like it is the same when driving along at low speeds in 4th I.e. The car is pulling even though the throttle is barely being touched.

I have unplugged the ECU for 30 seconds or so but it doesn't seem to have made any difference.

Any suggestions what it could be?

Edit - choke for chock.

Edited by pincher on Sunday 8th May 15:35

[Alexdaredevilz]

Try dissconecting the speedo under the arm rest right at the back under the little triangle,

[pincher]

Do you mean the lift out section? Just a load of fibreglass and a couple of screws under there?

[blitzracing]

It can be due to the basic throttle pot voltage being too high (so the ecu thinks the car is being driven, not at idle), or an errant speed speed signal from the Speedo calibration unit under the dash, again so the the ECU thinks the car is moving when its stationary.

[Alexdaredevilz]

blitzracing said:

an errant speed speed signal from the Speedo calibration unit under the dash, again so the the ECU thinks the car is moving when its stationary.

This is the problem with mine, and still no idea on how it can be fixed, as some one wired the immobiliser to it, but im going to save my moneys for a after market ECU at some stage

[MikeTVR]

Alexdaredevilz said:

This is the problem with mine, and still no idea on how it can be fixed, as some one wired the immobiliser to it, but im going to save my moneys for a after market ECU at some stage

The speed converter / calibrator is sensitive to electrical noise on it's power feed and speed input, which makes it continue to send speed pulses to the ECU when the car is statioary. Chims are notorious for poor earthing, so you could at least check the state of the earth strap under the offside front wheel arch which attracts lots of corrosion.

Mike

[TVR keith]

I've posted this before and some people have said it's b*ll*cks but it was reccomended by a TVR dealer and a TVR specialist and worked for me several times during my 6 year ownership of my Chim (sadly now sold).
With engine at operating temperature;
Disconnect electrical plug from stepper motor, ignition on for 10 seconds then turn off.
Reconnect plug, igition on for 10 seconds, ignition off for 10 seconds, ignition on for 10 seconds, start engine, hopefully solved the problem.
This is very quick and easy to do with no tools and its free, if any of you out there don't think it will work please don't bother telling me, I've heard it before, but it worked for me!

[blitzracing]

MikeTVR said:

The speed converter / calibrator is sensitive to electrical noise on it's power feed and speed input, which makes it continue to send speed pulses to the ECU when the car is statioary. Chims are notorious for poor earthing, so you could at least check the state of the earth strap under the offside front wheel arch which attracts lots of corrosion.

Mike

I can see a small service being set up here to keep these speedo boxes working here then Mike?

[pincher]

Thanks for the suggestions so far - I'll give them all a go over the next few days