There was another person exhibiting similar symptoms that turned out to be the pre-filter o-ring had not been installed correctly...certainly that is a very cheap fix, so why not try that first and see if it helps. Since it is sold separately from the filter many times it does not get replaced, but it should be!

Also, others have reported trouble with the K40 relay...more costly than the o-ring but not a wallet buster either...search under K40 to find other posts about it.

Good luck.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz