Not clear on what components make up the evaporative emissions system. Purge valve under the bonnet, piping to the charcoal cannister in the wheel arch and to the tank. Is there another solenoid valve to let air into the cannister? How much of the system is testable with full VCDS?

The reason I ask is I have codes (16786, 17912, 17961) pointing to inlet unmetered air yet again on the 1.4 16v fab. One year ago I spent a good week hunting this down with much help from board members, and failed to identify a definite cause. Complete inlet manifold off the car and strip down eventually, check for leaks, clean everything, refit and reseal every pipe and joint. New EGR valve fitted. Throttle body and EGR calibrations successful. This resulted in 10 months EML free motoring. Runs sweet as a nut still but the lights back. A quick throttlebody and EGR calibration has put the light out for the last 20 miles but it will be back.

My thoughts.

1 EGR failed but just replacing it last time did not cure the fault.

2 Faulty MAP sensor.

3 Evap fault.

4 Has there been a ECU update I have missed about this problem. There do seem lots of internet posts linking 1.4 16 v engines, 16786 and 17961, mostly without definite resolution.

5 I am hopeful the light will come on again while I'm driving (it's my daughter in London's car) so I can get a clue as to conditions that provoke it.

Anyone got any thoughts?

Don't think there are any other solenoid valves. Not sure which, if any, measuring blocks can be used to monitor purge valve function.

 

I agree I think that there is only one solenoid valve in the EVAP system.

 

Maybe not relevant, but one or two people with later Ibiza and Polo, especially in hot times of year, have had issues with difficulty starting their engines and replacing the solenoid sorted them out, there were no EVAP system faults being logged though.

 

Edit:-I suppose what I should have made clear, but I'd guess that you understand it, that as you are concerned about extra air coming in via a partially open EVAP solenoid valve, I was just giving you info about others that had similar "valve passing" issues while there being no system failures logged.

Edited 1 September, 20187 yr by rum4mo

This is aggravating. Have found another tiny leak in the vacuum plastic hose to the servo. Other end to the one last year.  Hose replaced. For some reason I had a length of airbrake hose which fitted. Walls are as thick as the hole down the middle. Also had the evap hose and engine breather hose off and the throttlebody. Gave em all a clean and re-sealed. Done 40 miles of mixed driving since and all is well.

I can't believe the tiny leak I found could produce these codes. If it is so then this engine and ECU is ridicouosly sensitive to airleaks. Time and more miles may tell.