After one year of production, only 125 units of the Islero were sold, so Ferruccio Lamborghini took the critics to heart and wanted to improve it, this resulted in the Islero 'S'-model, also called GTS. The exterior design was only slightly modified, little flares were added to the four wheel arches, a horizontal air exhaust appeared behind each front wheel while the front side windows now showed fixed triangular panes in their front portions. Small rectangular fog lights were installed underneath the front bumper and the rear window was now electrically heated, while a deeper intake on the engine cover fed air into the cockpit. The Lamborghini Islero S also came with tinted windows and round turn signals on the front fenders.
The greatest improvement could be found on the inside, the complete interior was redesigned from the original Islero, new seats with higher backrests at the front offered more comfort and were finished in leather on the sides with velours inserts in the center, many Islero were ordered with a full leather interior. The rear seat was split by a fold-down armrest, toggle switches replaced the earlier pull units and a glove box was installed on the dashboard, the dials on the dashboard were grouped more logically ... still, the major improvement could be found in overall workmanship ... the Islero S was just better made than the earlier model ... it made this one of the best-looking and best-performing 2+2 on the market back in 1969.
Changes underneath the bodywork were minimal, the old, square chassis from the 400 GT 2+2 was still used but the rear suspension was modified in line with the Espada suspension to improve stability under hard braking or accelerating, disc brakes were enlarged, and the engine was now up to 350 Bhp by installing camshafts taken from the Miura S and raising to compression to 10.8:1.
Still sales of the Islero S didn't boom, it seemed that all the improvements couldn't undo the bad reputation of the initial Islero, the workmanship was much better on the 'S' model but this didn't result in better sales. Even the different car magazines didn't spend much ink to this Lamborghini, they were all focused on the more impressive Miura and the larger Espada.
Only 100 Islero S were built, 5 of which came in RHD configuration, the final Islero S left the factory in early 1970, after only one year of production Lamborghini replaced her with the Jarama, today the Islero S is looked upon as one of the rare front-engined Lamborghini GT 2+2 models built back in the days when Ferruccio was still running the company, in fact during an interview he stated he preferred driving the Islero over a Miura or an Espada ... the Islero (both the GT and the GTS) are still among the much less well-known Lamborghini and don't demand the high prices as the 350 GT for instance ... in August 2015 a 350 GT (#0220) would be sold for $935,000 while an Islero S (#6531) would reach $401,000 at the same auction ... less than half.