Hi folks, my tdi is a wee bit down on power and im not sure what it may be. Changed the air flow meter but that made no difference and the turbo has that same whistle that it had when i bought the car many years ago, so im sure its fine. Its had one of those tuning boxes from ebay for 70 quid about 4 and a half years ago. During the winter it was playing up a little due to the very cold temps and displayed the engine management warning light. I would turn it down a bit and things would be ok. However this must have happened over a dozen times and once the winter was over i turned it up but was never convinced the car was quite right. Before, the box was turned well up (yes i know you shouldnt do that) but the performance was (i think) blistering! In a straight line my vrs cr tdi 170 would not have kept up, now however my old 1.9 just wouldnt keep up. The mileage is 76000 mls and the car is impeccably maintained/serviced. Does anyone have any ideas? Do these boxes have a lifespan?

Could be all sorts of things. I would get it on a reader and see if the ECU throws up any codes to narrow it down.

Yeah a mate of mine is going try that on Tuesday. Do you think it may pick up a problem in the tuning box? Would i be better removing the box first?

CTS I am wondering.... but fault codes are probably a good place to start!

CTS?

Coolant Temp Sensor.... is about £25 and can cause issues. Otherwise maybe MAF, MAP, n75, vacuum leak or sticky vanes. Some fault codes (if they exist) might help :-)

I was talking to a garage the other day (Skoda dealership) and they said they would just change parts until the problem was resolved. Ouch

Oh i dont like the sound of that! Ive ruled out the air flow meter as i tried a new one which made no difference. I thought of sticky turbo vanes but the car has onle done 76000 mls so im putting that to the back of the list. When the car checked for faults this week and doesnt show anything, i think i'l remove the tune box and replace with a new one and if that makes no difference i might just give up as the car still goes!

You could try removing the box for a while, disconnecting the battery to let the ecu reset, then let the car learn to drive without the box for a few weeks before reinstalling to see if that would change things.

I have a box fitted which i very rarely open up (unscrew) to adjust. perhaps you could have a look at yours to see if there has been any water leakage/ damage. i know i have hit my engine a blast every so often with the power hose but never thought about the box.

As an aside, i recently unistalled my tuning box to see what sort of effect it had on my mpg. With the box and measuring mpgs by brimming at each fill it was returning on average 51/52 consistently over 10+ fills. With the box of i have filled it three times and it has returned 58, 54 and 58 mpg respectively bit bored though, so may sacrifice 10% savings for wheel spin in gear in second every time.

I have also had issues with overboost with fault codes, but in my experience as was the case this time, any mechanical fault such as valves, turbo etc would cause intermittent power loss and not constant loss or reduced power. With mine its all or nothing!!.