Hi all, after some advice before I start replacing stuff / spending a fortune on what was supposed to be a cheap runabout..

 

T-reg 20v non turbo, 88k miles with full history .. the owner traded it in for a reason as it turns out 😕

 

Due to all the 'Short to Ground' issues I'm wondering if it might be a more central problem than the individual sensors. Car seems to drive OK, except for it dipping when you let off the throttle - revs drop to 5/600 and bounce 3 times before finding a pretty steady idle of 860rpm. However, looking at measuring blocks in vcds, this does fluctuate 840-870. It does this bounce whether you are sat still and blip the engine, or come to a set of lights. Temperature doesn't seem to make a difference.

 

Only thing I've changed so far is the ecu/dash temp sensor as this was showing an intermittent fault in 'Instruments' fault codes - replaced sensor, cleared code and has not come back (phew). 

 

A weird thing is there is no engine management light on on the dash .. but then it doesn't show up when you just turn the ignition on either, so I'm wondering if this has been disabled somehow for MOT purposes .. either that or it's been on so long it's burned out 😛 

 

Thoughts / advice welcome. Thank you

 

 

Address 01: Engine

6 Faults Found:

 

01247 - Activated Charcoal Filter (EVAP) System Solenoid Valve 1 (N80)

            29-00 - Short to Ground

 

17923 - Intake Manifold Valve (N156)

            P1515 - 35-00 - Short to Ground

 

17935 - Camshaft Timing Adj. Bank1 (N205)

            P1527 - 35-00 - Short to Ground

 

16486 - Mass Air Flow Sensor (G70)

            P0102 - 35-00 - Signal too Low

 

16518 - Oxygen (Lambda) Sensor B1 S1

            P0134 - 35-00 - No Activity

 

16519 - Oxygen (Lambda) Sensor B1 S1; Heating Circuit

            P0135 - 35-00 - Malfunction

There are those with more detailed experience of this area who I'm sure will respond in time but I'd be looking initially at connectors and/or possibly shared wiring that's been either damaged or mechanically stressed - such as occurs for door harnesses and the like.

 

Maybe look to see if the fault-code items share a common connection or earth?

 

@Simeon85 - This might sound like an odd question, but does the battery light come on when you switch the engine on, and go out when you start it?

Yes, battery light works as normal, I've also checked all the fuses and they look fine.

28 minutes ago, Simeon85 said:

Yes, battery light works as normal, I've also checked all the fuses and they look fine.

OK, it's not what I was wondering about then. Which is a pity, because that was a cheap and easy fix.

Yeah, I've searched Google and most people seem to solve multiple issues like this by replacing a fuse .. doesn't seem I'm quite so lucky.

 

The dipping idle may well be an air leak I believe from reading various threads, so I'm going to pull all the pipework off between Maf and throttle body and check it, then clean the throttle body and do TB adaption. See if that helps.

 

Worryingly, lots of replies elsewhere to things like this (mostly american sites to be fair) point at a knackered ECU (!), but I can't believe it would drive relatively OK if this was the case.

Edited 23 September, 20196 yr by Simeon85

The bouncy idle is likely the MAF failing if it is showing as a fault code. If you unplug it and that settles then thats that solved. If it stays the same then air leak searching time.

 

I remember someone posting a thread in the last 6months about all the earth point locations, and how cleaning and remounting them all sorted a lot of the "short to ground" issues they were having. How are the cable connections to the battery top fuse box looking? The black ones in particular, as there is a history of them corroding/burning out which can cause many electrical gremlins.

Yeah good shout on pulling maf plug off, I'll give that a go tonight - can you drive around with it disconnected, or not good for engine?

Its fine disconnected for a short testing run, the engine just defaults to a base line fueling rate, as it doesnt know how much air is going in. Probably be down on power, and throttle response etc might be off due to the engine not really knowing what its doing.

If the idle settles with it plugged out then get a new genuine one. VAG engines hate after market ones - it might work for a month, 6months or a day...

Disconnecting MAF made no discernable difference, must have an electrical issue or pretty bad air leak, need to find some time to get under the bonnet