My 1999 V70 R AWD has been throwing intermittent CELs, 3 or 4 ECM 644 codes over the last few weeks. Dealer reads them but the camshaft control tests ok. Dealer re-sets CEL and it returns - no pattern. Any ideas??? Dealer says the the camshaft control is about $600 for the part. YIKES! Is that correct?? ANy chance that this coul dbe caused by the electronic throttle control - I had software upgraded. Any chance it could be caused by mods - 3" downpipe or Denso Iridium plugs??