Fuel supply is suspect, check your filters.

The design of the CIS system uses fuel to provide counter-pressure on the Air Flow Meter, and low fuel pressure will result in rich mixture, high pressure in lean mixture (as the fuel pressure makes it more difficult for the airflow to lift the AFM plate and thus move the metering pin). This is supposed to be compensated to some point by the CIS-E system, but there is a limit.

My M103 car ran strong (bought new) until around 50k miles, always on Mobil premium fuel and driven ... spirited, then developed a hesitation like you describe when adding a slight bit of throttle. The dealer tried many things including fuel treatment and walnut-shell blasting of the valve stems to remove carbon (carbon? In my car? NOT) with no changes. I also had the entire fuel distributor replaced, no change.

I found only one fix: RedLine Fuel Injector Treatment (or something like that, but it is RedLine and I currently buy it at O'Rielys). None of the solvent-based "cleaners" like Techron (dealer tried that too) had any effect, this stuff worked, the guys at RedLine (I use their oil anyway) told me that it is a detergent based cleaner, and that solvent-based cleaners are so diluted in the fuel that they don't have a chance, ... plus they're corrosive and you need to change your oil after using it. Anyway, this is the nature of the CIS system, and fuel dribblers don't work as well as fuel injectors (fine spray), especially at low flow rates. I started running this stuff in all of my CIS cars (VW, Audi, and Porsche) and it cleaned them all up.

So it seems like a lean mixture, check first for vacuum leaks, very likely, ... then try a $10 bottle of RL cleaner, ... if that doesn't work then

Good luck,

__________________

Gone to the dark side

- Jeff