idle sensor problem

[alex200mph]

Had my car serviced a few months ago and they said that the idle semsor is faulty/not working. I have noticed that the car stalls when it comes up to junctions occationally. Apparently its something to do with the fact that the ecu doesnt realise that the car has come to a stop. Now that I have done my mirrors so the electric motors work (thank you fellow phs for your help with that one) I want to sort this idle sensor out if possible. Its quite annoying when the car stalls at junctions. Can anybody help.It would be much appreciated

Where is the sensor? Is it very easy to replace? What should I look for?
Many thanks
Alex
nb hope everybodys 2003 has got off to a good start.

[shpub]

There is no idle sensor. There is a speed input to the ECU and an idle controller aka stepper motor. You can clean the stepper motor but there is not much you can do for the speed sensor as it requires an oscilloscope to check the pulse train it generates and you would need to check that that signal is going to the ECU. The big question is if it was picked up at a service why wasn't it sorted out then?

Steve
www.tvrbooks.co.uk

[plipton]

Steve's right (as ever). It should have been sorted at the service. However, the problem still exists.

I had a similar problem and cleaning the stepper cured it..

www.pistonheads.com/gassing/topic.asp?f=66&h=&t=22349

[alex200mph]

Thanks for your reply guys, much appreciated
I have cleaned the stepper motor in the past as per the bible and it does make the car idle better. However the problem is still with the ecu not getting the correct information on if the car is moving or stationary I belive.

Steve, the problem was picked up at the service about 3 months ago when they plugged in the diagnosic equipment, it said that the ecu was not getting the correct info so it didnt know when the car was stationary hence the stalling. I guess this diagnostic equipment is an osciliscope or similar. They said that they could not set the low speed or idle mixture till this was sorted out which is a little rich on my car. They said that they did not have the component in stock so I would have to book the car back in. Havent got round to doing it and while I have got some time I though i might have a go myself. So if I know that they ecu is not getting the right info can I replace this component or do anything to help the problem?
Many thanks
alex

[shpub]

The ECU diagnostic equipment is not a scope and is usually a block box fault code reader. All the fault code says is that the ECU is not seeing the speedo input which could be down to set of things like bad connections/wiring to duff speedo sensor (£150) or speedo (£300 or less for a recon). It could also be a stepper motor fault code. in which case the stepper may need replacing.

Yes you can go and buy the bits and replace them but that is no guarentee that they will cure the fault as ther could be other issues. I think you would be better off taking the car back and saying fix it please.

[alex200mph]

Sounds like I could go to alot of trouble and not even fix the actual problem so I think I will get the garage who serviced the car to fix it for me then. Many thanks for you help steve.

[griff2be]

Alex - first the mirrors, now the speed sensor. I feel like I'm being stalked in a TVR problems type way!!

I have (well the GrifF does) exactly the symptoms you describe - stalling coming into junctions. The ECU fault code read 68, which is a speed sensor fault. I had a new coil (no change, stepper motor (no change) and finally a new speed sensor. Guess what, the damned thing is still doing it every now and again!!

I haven't driven the car much or had the fault code reader on the car since the new sensor was fitted(which, btw, is fitted close to the diff on the o/s rear - its a screw in cylinder shape about an inch in diameter, that fits close up to the castellated ring on the o/s drive shaft coming out of the diff).

I hear rumours of there being an amplifier on this circuit which amplifies the signal going to the ECU or speedo or both. Maybe that's my problem - as frankly there's not much left to change! Fortunately warranty took care of everything on mine other than the coil - but Steve is right, it could be costly using the trial and error method!

I don't know whether a rolling road session would help get to the bottom of it quickly and accurately. Any views Mr Heath?

Regards

Andy

Edited to say that taking it back to the dealer and saying 'fix it please' has resulted in a new speed sensor and stepper, but not fixed the problem in my case...

>> Edited by griff2be on Tuesday 7th January 23:27

[shpub]

Fault code readers are wonderful things but don't give you all the detail so they need to be used with a pinch of salt. They can tell you what but not why and with speed faults, there are many reasons.

Speed sensor problems need to be tested with the wheels moving and that is dangerous in itself. A rolling road is safer in that respect but any investigation needs to start at the ECU end and chceking that there is a signal arriving at the ECU. This could be a wiring fault etc. A scope is the only real way of seeing this. If the signal is there then there is a fault in the ECU. If not the investigation has to start going through the rest of the wiring. Now we are into dash off, instruments out type of scenarios and so on. The signal pulse and when it occurs is also important as some of the sensors rely on the wheel speed to activate and if this is not fast enough, no signal but sufficient to drive the speedo.
These are not easy things to investigate. This is why the speedo and road sensor section in Bible 2 exploded because it is noit straightforward.

Yes it may well be a rolling road session. Those wheels need to be moving to see what is going on.

Steve

>> Edited by shpub on Wednesday 8th January 09:54