Golf Mk5 2.0 FSI - Fluctuating/High Engine Load when car is just idling

[garymansell]

Hi,


I noticed what I think is something strange the other day when I was investigating an intermittent implausible value coming from the Brake Boost Pressure Sensor (G294), I wonder if anyone knows if this behaviour is to be expected or not and what might be causing it?


I was using the VAG-COM to monitor the Intake Manifold Pressure and the Brake Boost Pressure Sensor, and at the same time, the Engine Load happened to be one of the values also being displayed.


The car was idling at 800rpm, (Air con and other things off) and the Brake Boost was reading a steady 250mbar, the Intake Manifold a steady 400mbar and the load was a reasonable 15%. Then, after a while you could hear a slight change in the engine note and the revs would fluctuate a little bit, but the load would go up to about 35%, the Brake boost up to 400mbar and the Intake Manifold pressure up to 600mbar. It would sit like this for a minute or two and then revert back down to the lower values again and then back and forth repeatedly.


Now I come to think about it I wonder if this is related to a strange feeling on the brake pedal I have noticed when I am stopped and idling at traffic lights. After a while of sitting there with my foot on the brake, I feel the brake pedal give a bit and the note of the engine changes.


As far as I could tell, there was no load such as Air Con / Fan etc. kicking in to increase the load, and surely at idle 35% load is pretty high for a vehicle at idle?


Can anyone shed any light on this behaviour?


Rgds


Gary

[towcestervag]

check the engine pcv valve on the front of the cam cover as these fail and will cause the engine to run roughish and cause engine load and intake pressures to alter