Fabi returned with Porsche Motorsports in 1990 to drive their No. 4 Foster's-Quaker State March 90P-Porsche Indy V8. Prior to the start of the season Porsche was going to build an all carbon fibre chassis with their constructor, March Engineering. In January, Porsche's competitors voted against the use of the car and as a result Porsche had to use the year-old March 89P chassis. Fabi qualified seventh at the Toyota Grand Prix of Long Beach on the but finished tenth. A new March 90P was used at the Indianapolis 500 and Fabi started twenty-third and retired in eighteenth due to transmission problems after 162 laps. Fabi later qualified on pole position for the &lt;a href="Grand%20Prix%20of%20Denver"&gt;Texaco/Havoline Grand Prix of Denver&lt;/a&gt;.He led one lap but crashed after seven laps and finished twenty-seventh. Fabi achieved a best finish of third, at the Marlboro Grand Prix at the Meadowlands, at Meadowlands Sports Complex, and ended the season fourteenth in points. At the end of the season Porsche withdrew from Indy car racing so Fabi moved to the World Sportscar Championship in 1991 and won the championship.