# EPC light on, pulsing revs and now it won't start!



## NAFE_P (Sep 27, 2009)

Had an issue last week when I stopped at my mates for 5 mins, got back to the car and it wouldnt start. I waited for a bit an did start but the EPC light came on, the revs were going up and down, idling at about 1600 and it felt a tiny bit hesitant to drive.

The next day it was fine and has been for 3 days but now it's doing it again, the EPC light came on when i was driving from home but i got home and now it wont start again. It's due a service in 500 miles so may will just book it in early and get them to take a look. Any ideas what this might be and should I be driving it with this happening?

Cheers
Nafe


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## djdougalno1 (Jan 11, 2010)

Could be crank position sensor but needs to be scanned and see what codes come up would be good to scan it when it won't start as some codes clear when it's only an intermiten problem


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## peter-ss (Sep 3, 2008)

I had an issue with the EPC light coming on and giving me very limited throttle. 
It comes on if a fault is detected with the Electronic Power Control, which is pretty much your accelerator pedal and throttle body.

The EPC works using a fail safe system where the accelerator pedal has two potentiometers in parallel and the feedback on the throttle body has the same. I seem to remember that although the potentiometers operate in tandem their signals are the exact opposite of each other. The idea being that if the signals aren't what the ECU expects it flags it as a fault and limits the throttle, to prevent a full throttle condition in the case of a fault.

A Vag-Com scan will tell you what the problem is; on mine after logging the signals back from the throttle body, I spotted that one of them had a glitch at a certain point. Very carefully removing the panel from the throttle body and cleaning the potentiometer tracks fixed the problem.

_Why do so may of my posts start with 'I had an issue with'? is there anything that didn't go wrong on my Mk1?._


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## NAFE_P (Sep 27, 2009)

Thanks very much, I'll call the guys at Dialynx tomorrow


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## NAFE_P (Sep 27, 2009)

djdougalno1 said:


> Could be crank position sensor but needs to be scanned and see what codes come up would be good to scan it when it won't start as some codes clear when it's only an intermiten problem


Good work, that's exactly what it was! Had it replaced and now it's all good


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