brace yourself for this one!.got a 91 jap tt thats devoloped an overnight fault since last thursdays down pour even though it wasnt driven.the cars tickover has dropped to 500rpm.when i start the car the battery and abs lights stay lit until i rev it then the battery light goes very dull and the abs light goes out but then the LIGHTS warning lamp comes on even with the lights off!the idle valve now doesnt respond to engine loads ie if i turn the heater or lights on the revs die.checked voltage across battery when the warning lamp was illuminated brightly.reads 12.5v :headvswal until the engine is revved then it jumps to around 14.5v.my first assumption was a short caused by a water leak on my leaky targas which i fixed today.when i checked the consumer board and ecu they are both dry.ecu check came back code 55.has anybody had an altenator go and it caused weird faults on their car,thats if it is the altenator.oh and my factory boost gauge refuses to move!!.all this has started at once with no warning.need help on this one guys as ive never came across this in 16years as a mechanic.

sounds like a bad earth like. the alternator seems like its charging. because the tickover is so low it probably wont charge till about 750-800 rpm, hence why u have to give it throttle to get 14.5V so its prob ok.

have you checked ALL the fuses both fuse boxes in the engine bay and the one at the drivers footwell?

Jesus mate i've got a sim issue...but everytime i wash the motor the horn goes off and f@cks all the light headlights...i end up having to rip out a couple of fuses until it drys out!!

 

Must be an earthing issue unfortunately these are not easy to find mate....i had someone strip it and check over the wiring and they repaired some but there must be more split wires somewhere :(

 

A good auto leccy should be able to help u.

thanks for the replys.best get my electrical head on!!