In an open letter to the company's shareholders, Icahn criticized past moves at Time Warner, such as selling Warner Music Group and Comedy Central at discounted prices and its failure to acquire MGM, according to a filing with the U.S. Securities and Exchange Commission.
Icahn, who is backed by three hedge funds that hold a combined 2.8 percent stake in Time Warner, also reiterated his recommendations that the company initiate a $20 billion share buyback and spin off 100 percent of its Time Warner Cable unit.
A representative of Time Warner was not immediately available for comment. But the company has already pledged to buy back up to $5 billion in stock and spin off a 16 percent stake in the cable company.
"Unless this legacy of poor decision-making is fully recognized and the board is held accountable, the dismal record of mistakes and inaction will continue to the detriment of shareholders," Icahn's letter said.
Over the last three years, Time Warner has been credited with cutting its net debt to about $13 billion from as much as $30 billion early 2003. It also settled lengthy government probes and shareholder suits following the merger of Time Warner with--now known simply as AOL.
Chief Executive Dick Parsons has said he would consider spinning off a larger stake in its cable unit over time, but he believes the current 16 percent plan is appropriate.
Fulcrum Global Partners analyst Richard Greenfield said the pressure on management and discussion of an alliance between AOL and Microsoft's MSN would help boost Time Warner shares in the near term.
Time Warner and Microsoft have been discussing ways to combine their Internet assets, including the possibility of an investment by the software giant.
"There are a lot of moving pieces right now," Greenfield said. "I think all of them bode well for Time Warner shares in the near term."
Greenfield also said Time Warner could increase the size of its share buyback. "It sounds like management is committed to increasing the level of capital return," he said, "and I would be surprised if the buyback didn't increase notably over the course of the next couple of months."
Icahn, known as a corporate raider and for his agitating tactics at Blockbuster and Kerr-McGee, revealed his interest in Time Warner last month and indicated that he would seek a seat on the company's board.
In Tuesday's letter, Icahn said Time Warner's "cardinal sins" date back to its merger with AOL, which led to the loss of more than 75 percent of market value over two years.
He said 12 of the 15 current Time Warner board members, including Parsons, supported the merger and questioned whether they should still be "steering the corporate ship."
When pointing out what he calls past failures at Time Warner, Icahn also noted its bloated cost structure, saying his coalition intends to hire an industry consultant to analyze and compare the company's costs with those of its peers.
Icahn concluded that Time Warner's past missteps indicate the need for new management.
"But whether or not you agree with our proposals," the letter said, "we believe the simple truth is that Time Warner is a company sorely in need of new shareholder representation on the board."