Federico,
You also should tell us if your 1985 Porsche 928 is a North American 32-valve motor (with catalytic convertor) or is a Euro/ROW model that is 16-valve - I would guess that either model may be sold in Mexico. There are considerable differences, the easiest way to tell is to look at the intake manifold; the 32-valve motor is covered with pipes that run parallel to the ground (you can barely see the engine), the 16-valve motor has an intake system that looks like a spider standing up on the 8 legs (intake runners).
The 32-valve motor has Lambda air/fuel regulation and an O2 sensor to go along with the Cats - the Lambda system automatically regulates the air/fuel ratio. It also has automatic idle speed regulation. The Euro model air/fuel ratio is static set at 0.5 - 1.5% and HC PPM less that 300 set at the MAF and the idle speed is static 700 - 750 RPM set at the throttle body.
For 32-valve motor owners, please be aware that it is necessary to set the base CO% (air-fuel ratio) at 0.4 - 0.8% with HC less than 300 PPM and idle speed at 660 - 700 RPM for your motor to run correctly. Instructions are in the factory workshop manual.
If your 928 doesn't have a service history, or if the cam belt hasn't been changed in the past 20,000 miles I suggest that the cam belt and water pump be changed and the tensioner roller bearings be inspected. It is an interference motor so if the cam belt slips or fails the valves will hit the pistons and a very expensive repair job involving removing the heads and replacing valves will be required.
Rich
Membership Chairman
Charter Member
1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed rescue
1979 928 5-liter track beast
