A B757-200 AT FL260 DIVERTED DUE TO ODOR OR FUMES WHEN ENG PWR ADVANCED; TKOF; CLB AT 10000 FT AND AT FL230. ODOR LASTED LESS THAN 5 SECONDS.

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ON TKOF AT V1 -10 KTS; SMELLED ODOR IN COCKPIT THAT SMELLED LIKE RUBBER. THE ODOR LASTED FOR A FEW SECONDS AND DISSIPATED. NEVER SMELLED RUBBER ODOR AGAIN DURING THE FLT. AT 10000 FT; ATC GAVE US A CLRNC TO CLB TO FL230. JUST AFTER CLB PWR WAS SET; SMELLED AN ODOR SIMILAR TO FOOD BEING OVERCOOKED IN THE OVEN. CALLED THE FLT ATTENDANT AND ASKED IF THERE WAS FOOD IN THE OVEN AND IF THEY SMELLED ANYTHING. THE ANSWER TO BOTH QUESTIONS WAS 'NO.' AGAIN AT FL230; AND AFTER ADVANCING PWR; THE FUMES REAPPEARED. CALLED THE FLT ATTENDANT AND AGAIN ASKED THE SAME QUESTION. AGAIN THE ANSWER WAS 'NO.' I FAILED TO MENTION THE FUMES LASTED FOR LESS THAN 5 SECONDS. ACFT WAS LEVELED AT FL260. COMPANY WAS INFORMED AND DECISION WAS MADE TO RETURN TO PHL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT ON CHKING BACK WITH MAINT SEVERAL DAYS LATER; THE CAUSE OF THE ODOR OR FUMES WAS STILL UNKNOWN. THE RPTR SAID MAINT WORKED FOR 10 HRS INSPECTING AND RUNNING THE ENGS BUT COULD NOT DUPLICATE THE RPT.