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My 2011 1.6 TDI 75kW VW Caddy with 259.000km has this problem, where after some time on highway it starts to lose power when I stop, turn off the engine and start it again it goes away sometimes, and/or it happens again after a few minutes. It all started last summer in july after around 45 minutes in the car total and 30 minutes on highway i had cruise control on at 116km/h and there was a slight hill and the revs just started going down, even if I floored it it didn't do a thing. But after I stopped and restarted the engine it went away and no such thing happened again until June this year. This year I often do a trip around 130km on each direction, first it is around 30 minutes and 35km of non urban roads and then around 100km of highway and three times the car experienced a loss of power in nearly identical spot just after a bit of a hill. The next time I drove this route it was hotter(around 34 degrees C) and this happened almost every slight uphill on highway. Sometimes then it starts to come back but the power then drops back down again and i am stuck going around 80-100km/h. It has been to a shop but because no warning lights come on they don't know what is the matter. They said that it might be something with the EGR valve but until a light comes on they are not sure. Last week I was driving in that direction again and as soon as there was a slight uphill it started having problems again. I should also mention that when the power loss happens the fuel economy matches the speed, so even if i floor it it stays the same as if i would want to go the speed that I am forced to go because of the power loss. There is no impact on shorter trips like through city and non urban driving. I have also tried driving on highway without cruise control and driving faster than usual but it happened anyways. Could this be somehow connected with temperature? This didn't happen through winter. Or with uphills? On the way back there are less pronounced uphills and it didin't happen as mutch. I would REALLY appreciate the help, it is driving me mad.

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  • Typical symptom of the exhaust gas regeneration valve being crudded up. Get a diagnosis. The EMS kills the turbo, which on these VAG engines should typically run all the time. Until fixed, drive with very gentle acceleration, and avoid steep hills, especially don't try to hold your speed going uphill, or accelerate uphill.
    – Weather Vane
    Commented Jul 15 at 12:05
  • ...there is no warning light from that, just limping until stopped and restarted. It doesn't affect much around town, because the power demand on the engine is light. But out on the highway, more power is needed (it's roughly proportional to the square of the speed), especially on hills, and particularly when accelerating uphill.
    – Weather Vane
    Commented Jul 15 at 14:41
  • Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
    – Community Bot
    Commented Jul 18 at 12:21

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You have symptoms of a failing Mass Air Flow sensor (MAF). The loss of power means that the engine has gone into "limp mode". Limp mode lasts only as long as the engine is running. When you re-start it, the engine goes back into normal mode.

There is a fairly easy way to see if this is your problem:

  • When you have some time, find the MAF on your engine and practice disconnecting and reconnecting the electrical plug. If you don't know where it is, search for diagrams or images online for your specific vehicle.
  • The next time you have a power loss as described, get off the highway to a safe place to park, do not turn off your engine, and disconnect the electrical plug on the MAF.
  • Get back on the highway and drive. Your check engine light will be on, but this is just a warning that the MAF is disconnected, no worries. If you now have greatly improved power, maybe 85% of normal full power, this is diagnostic of a bad MAF.

When the ECM loses its connection with the MAF, it substitutes a reasonable average value for mass air flow in its computations. This restores most of your power.

When you reach your destination, please reconnect the MAF connector so you do not produce excess emissions, and the next time you start the car, the check engine light will remain off. You should consider changing the MAF as a permanent solution, perhaps after confirmation by a shop.

I should point out that any well equipped shop with the proper testing equipment for VW TDI should have been able to diagnose this problem in a few minutes, even with no check engine light. I recommend that you find a shop with expertise in VW diesels.

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  • I have tried both things recommended. The MAF sensor made the problem worse for that time. Then I changed EGR valve and the problem remained the same. Ideas?
    – arthorus
    Commented Aug 22 at 7:34
  • @arthorus Sorry, no more ideas. You need to find a shop that is experienced in VW diesels and equipped to scan the ECM and all relevant sensors. Replacing parts based on a hunch is a terrible, expensive way to fix the problem. The money you wasted on a replacement EGR valve that did not fix the problem could have paid for all or most of a professional diagnosis. Diagnose, then adjust or repair as needed. Don't let anyone replace parts unless they guarantee that the replacement will fix the problem. If they can't make that guarantee, they are just guessing.
    – MTA
    Commented Aug 22 at 13:00

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