Icahn sweetened his offer for Pep Boys for the second time to $18.50 per share on Monday, after Bridgestone raised its bid by $1.50 to $17 per share on Dec. 24. Pep Boys said on Monday Icahn’s latest offer was superior to the deal it accepted from Bridgestone, and moved to terminate its agreement with the Japanese company. Icahn, whose latest bid values Pep Boys at about $1 billion, had reported a 12.12 percent stake in Pep Boys earlier in December and said the company’s retail automotive parts business would be a perfect fit for Auto Plus, a competitor he owns.