first off, did that mechanic talk out of his butt or his mouth? Thats the biggest crock of ---- I ever heard.
When you installed your KKM did you reset the PCM? (disconnect the negative terminal from the battery for at least 30 sec.)
If you did reset the PCM then remove the KKM and re-install the stock filter and reset the PCM again and see if the problem persists. This will identify if the KKM is at fault.
Second, it is possible that the KKM was oiled too heavily and has contaminated the MAF. IF you find the MAF is contaminated I believe it can be cleaned with throttle body cleaner, while it is removed from the viehicle. again after cleaning the MAF reset the PCM.
