Lindsay Lohan has vowed to stay sober at the Coachella Valley Music and Arts Festival.

The troubled actress - who is due to check into court-ordered rehab in the coming weeks - has told friends she just wants to have ''fun'' and check out the ''music'' at this month's Californian festival, and, according to gossip website TMZ, she has pledged she won't touch drugs or alcohol during her days at the event.

Lindsay's father Michael Lohan has slammed her decision to attend the festival as the ''worst idea'' she's ever had.

He said: ''I think it's probably one of the worst ideas she could ever have had. What did the court say? Stay away from people and places where there might be drugs or alcohol.''

And the showbiz patriarch is unconvinced that the 26-year-old star's stint in rehab will be successful.

He said: ''I'm praying to god she will succeed. But honestly? I hope so but I don't think so.''

It was recently claimed Lindsay only agreed a plea deal - which related to charges she faced over a car crash last June - because the terms of her attending rehab meant she didn't have to go until after Coachella.

A source said: ''Lindsay was adamant that she not be forced to go to rehab until after the Coachella Valley Music and Arts Festival in the Palm Springs area on successive weekends in April. Lindsay loves going to the musical festival, and she's determined to go this year.

''She didn't want a little thing like rehab to get in her way of attending. Lindsay refused to sign off on any deal that would have prevented her from going to Coachella, period. Yes, it's that important to her, for some strange reason.''