Stepper Motor sluggish?

[fergusg]

I have a problem when cold that my car tends to idle fast, up to 1500 until I stop at which point the revs will drop off back to 900. I have cleaned the stepper motor and seat and the throttle butterfly. I have also reset the base idle as suggested in Steve Heath's book. When doing this I noticed that when I release the ar bypass pipe to bring the revs back up after setting the base idel to 500rpm, the revs go quite high 2,000-2,500 (not sure as I am not in the drivers seat at the time) and stay there for a few seconds. I presume this is because the stepper motor is wide open whilst the bypass is pinched trying in vain to bring the revs up. I am wondering how quickly the stepper motor should get this under control as it makes me wonder if my stepper motor is sluggish, or sticking, and that is what is causing my ticover problems when cold. I would appreciate anyone's thoughts, particularly anyone else's expreiences from setting the base idle.

[spend]

Could be faulty speed sensor signal to ECU. Lucas fault reader would probably tell you. Early cars are fed from the LT77 gearbox drive, Later cars thru magic splitter box in dash.

Dave

[Ricardo Bertone]

After any fiddling with the under-bonnet stuff it's always worth resetting the ECU - switch off, disconnect the ECU connector, go have a cuppa and then reconnect.

Ricardo

[smb]

this can be cuased by the ecu think,ing it's too cold and adding further enrichment, check also the ecu coolant temp se nsor

[fergusg]

spend said:

Could be faulty speed sensor signal to ECU. Lucas fault reader would probably tell you. Early cars are fed from the LT77 gearbox drive, Later cars thru magic splitter box in dash.

Dave

Thanks Dave,

What does the speed sensor do?

[fergusg]

smb said:

this can be cuased by the ecu think,ing it's too cold and adding further enrichment, check also the ecu coolant temp se nsor

Thanks, I'll test the resitance at different operating temps.

[fergusg]

Ricardo Bertone said:

After any fiddling with the under-bonnet stuff it's always worth resetting the ECU - switch off, disconnect the ECU connector, go have a cuppa and then reconnect.

Ricardo

Thanks, Not sure what this does. The ECU adapts to the engine condition as I understand it. If you mess with stuff under th bonnet, won't it just adapt again given time?

[Ricardo Bertone]

Sometimes the ECU gets a bit lost when things have been altered so resetting puts it back on the fuel map.

Ricardo

[symonab]

The ECU only resets the idle map from what I understand. You have to reset the ECU start the car up and get her up to operating temp. Once at 90 degress or above then the ECU will reset the idle map as long as 3 conditions are met.

1) Coolant above 90 degrees
2) engine at idle continually (ie not blipping throttle)
3) No forward speed

Sy

[fergusg]

symonab said:

The ECU only resets the idle map from what I understand. You have to reset the ECU start the car up and get her up to operating temp. Once at 90 degress or above then the ECU will reset the idle map as long as 3 conditions are met.

1) Coolant above 90 degrees
2) engine at idle continually (ie not blipping throttle)
3) No forward speed

Sy

Sy,

So do I need to reset the ECU by unplugging waiting and then plugging back in and then follow the above to get it to remap? Or do I not need to unplug the ECU?

Thanks

Adam

[spend]

fergusg said:

What does the speed sensor do?

Keeps the engine turning when the wheels dont.....

[HarryW]

symonab said:

The ECU only resets the idle map from what I understand. You have to reset the ECU start the car up and get her up to operating temp. Once at 90 degress or above then the ECU will reset the idle map as long as 3 conditions are met.

1) Coolant above 90 degrees
2) engine at idle continually (ie not blipping throttle)
3) No forward speed

Sy

I was told to keep it running until the fans cut in and out again for a proper relearn cycle.

Out of interest after resetting the base idle if you are not sure of the position of the stepper you can switch the ignition on (don't start) and off again three times to get it fully housed (reset). Then do the start and let run without touching anything until the fans cut in and out, then switch off........ it has then relearnt idle.

Re the 1500rpm whilst moving, I thought this was normal, it keeps the revs up whilst changing gear etc, with zero speed it then drops down to 900ish. This is determined by zero throttle and the speed sensor feeding the ECU, if the speed sensor was fecked then it drops straight down to 900 even when moving with zero throttle.

[rfisher]

Fergusg - you don't permit receipt of emails through PH for some reason.

If you want a fault code reader pm me.

[Cider Andy]

fergusg said:

I am wondering how quickly the stepper motor should get this under control as it makes me wonder if my stepper motor is sluggish, or sticking.

I've seen numerous reports of this. My own car behaves like this, but only in certain circumstances (that I haven't completely isolated). I reckon it's 'normal' behaviour, not a problem with your stepper motor. Try firing the engine up with it removed from its seat but still connected: it reacts pretty quickly! More likely a 14CUX software issue, I'd think.

[fergusg]

spend said:

fergusg said:

What does the speed sensor do?

Keeps the engine turning when the wheels dont.....

My left foot normally serves this function

[andy11]

Hi Adam, If you are still struggling try giving Dan Melladay a ring in Skellingthorpe, top bloke, knows TVR's, may give you some idea's. I went to check him out this year and was impressed with his knowledge. 01522 509099
Cheers
Andy

[Ricardo Bertone]

Fergusg

Do you drive with your legs crossed?

Ricardo

[spend]

Maybe he has an RFD (Right Foot Drive) Car ? :-)

[fergusg]

Ricardo Bertone said:

Fergusg

Do you drive with your legs crossed?

Ricardo

No, but when the wheels stop turning the engine has a habit of stalling if I don't straighten my left leg.

[fergusg]

andy11 said:

Hi Adam, If you are still struggling try giving Dan Melladay a ring in Skellingthorpe, top bloke, knows TVR's, may give you some idea's. I went to check him out this year and was impressed with his knowledge. 01522 509099
Cheers
Andy

Thanks Andy, how's the T350 wor going?