If I remember correctly, he fell off the road and retired at the first lap, first corner in the first 4 races. Even when he survived the first lap he was way back in the running order.
He was useless in F1
He was lured to McLaren by Ron Dennis promising that they would have the Renault V10 rather than a Ford V8 that wasn't even as high a spec as the one in the Benettons. He started out in F1 just as the FIA announced new limits on in-season testing and a cap on the number of tyres allocated for race weekends. As for the races:
1) In his first race the gearbox malfunctioned and he didn't get away at the lights, he later got going again but got into a fracas with Derek Warwick and wiped a corner off his car.
2) Round 2, and he's taken off at turn 1 by Berger in an almighty smash.
3) Donny Park, and Wendlinger takes him off halfway around the first lap.
4) 4th round at San Marino, his car malfunctions in practice and spins him off. Everyone says it's his fault, despite the same thing happening to Senna a few times. Then in the race he's battling for 4th when his rear brakes....um....break.
5) Spain, and he finally makes it to the flag in 5th.
Time and time again that year he got taken off by someone else, or the car ****** up. Yes, he should have tested more. Yes, he shouldn't have commuted from the States like his Dad did before him. Yes, he did make a few mistakes himself. But "useless in F1"? People always seem to forget his storming drive from 16th on the grid in Magny-Cours (after another car malfunction in qually) up to 6th. Or his podium in Monza. Or the fact that McLaren put him under pretty horrendous pressure by announcing to him early on in the year that they had Mika waiting in the wings if he didn't up his game. Or the fact that McLaren lied about their engine deal to get him to join the team (McLaren lie? Surely not!).
He didn't do himself any favours, but neither did McLaren.