Author Topic: Service mode bad idling  (Read 313 times)

Offline Mark Millington

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Service mode bad idling
« on: January 28, 2018, 03:05:01 pm »
Hello chaps

My g40 is lumpy on idle and won't go into service mode when blue temp sensor is unplugged. Have recently replaced all earth straps battery voltage is good and runs at nearly 14v when running. Has had new dizzy rotor arm blue temp sensor etc. Even turning the idle screw on back of tb doesn't seem to change alot runs fine when driving but boggy at low revs and idle has a mind of its own. Anyone got any ideas

Thanks Mark

Offline hayesey

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Re: Service mode bad idling
« Reply #1 on: January 29, 2018, 08:56:48 am »
faults like this can be a pain!

I'd start off by fault code reading the ECU to see if it'll tell you what it's not happy with.  Some info here:

https://www.polog40.co.uk/forum/index.php?topic=213.0

You'll need a "vagcom" lead with a 2+2 adaptor.  There's loads of them on ebay, you'll want a lead for the really old software version (something like 3.11).  You might also find that the VWTool.exe program you can download in the above link works better on a G40 than the proper vagcom software.

Hopefully that'll tell you which sensor(s) the ECU isn't happy about.  Before you start spending money on new ones, check the wiring from the sensor to the ECU.  There's an ECU pin out here:

https://www.polog40.co.uk/forum/index.php?topic=211.0

If you have a haynes manual, that's useful too.  Just use a multimeter and do a continuity test on the wiring.

If the wiring is OK then try swapping the sensor(s).

I had a similar fault years ago which took me a while to trace, fortunately I had a Polo GT at the time too so could swap sensors between the two rather than just buying new ones.  In the end it turned out to be the ECU itself that was faulty.  I only found out after trying pretty much everything else and then borrowing a spare ECU from a friend out of desperation. 


Offline Mark Millington

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Re: Service mode bad idling
« Reply #2 on: January 29, 2018, 01:20:48 pm »
Thanks for the reply. Appreciate any help. I'm ok changing mechanical stuff but not so good with electrics. Think I'm going to change the lambda sensor see what happens if that fails might have to find a specialist somewhere  to book it in local to me. In really hope it ain't the ecu as I bet trying to find one of them will be impossible! Trouble is where it's not going into service mode when warm can't check the timing etc can I?

Mark

Offline hayesey

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Re: Service mode bad idling
« Reply #3 on: January 30, 2018, 02:36:44 pm »
no you can't do the timing properly if it's not going into service mode.

I think it's unlikely to be the ECU, just using that as an example of how it's not necessarily just a sensor being faulty. 

Offline Mark Millington

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Re: Service mode bad idling
« Reply #4 on: February 01, 2018, 11:09:37 am »
Thanks bud guna set the co pot can you do that using a multimeter on puns 1 and 3 when the car is off or on? What other sensors woukd you suggest looking at sorry for all the questions have done the temp ones with geniune parts also the idle on the throttle body on the back this can only be adjusted when in service mode too? Is there a base setting to start with eothbthat I.e in or out etc

Thanks Mark