When starting the car from cold, for the first 20 seconds or so it seems to idle fine every time (I'm guessing during this initial period the ECU is using some fixed, preset fueling/ignition map?). After this it begins misfiring irregularly but quite frequently, sometimes several times in a row but usually a few seconds apart. Each time it misfires it spits a small amount of fuel out of the exhaust but no blue/white smoke or anything. If I depress the accelerator very quickly then the engine will bog down/stall completely or backfire through the inlet manifold. Once the engine has reached operating temperature the problem seems to be a bit better. It still misfires occasionally but doesn't spit fuel out of the exhaust and no longer bogs down/stalls under rapid depression of the accelerator.
The engine is a freshly rebuilt & run in 1275 with new piston rings, new valve guides, valve stem seals, oil pump, water pump etc, Kent 274 cam & duplex timing gear, standard forged rockers, standard airbox with a K&N element. Compression is good on all cylinders, it isn't using any oil or water and under normal driving conditions doesn't seem to have any issues, though is perhaps running a bit rich as under hard acceleration or engine load there is a smell of petrol inside the car.
So far I have checked/changed the following with no success:
- Valve Clearances (Checked and rechecked after about 100 miles, set to a "loose" 12 thou)
- New spark plugs, HT leads, Dizzy cap and rotor arm (After some mileage the plugs don't seem to show signs of rich or lean running, neither did the old plugs)
- Changed the coil for a known good one from another SPI
- Replaced all the vac hoses and cleaned out the fuel trap
- Removed the ECU and cleaned the MAP port with some cotton wool on a radiator overnight
- Checked the lambda heater relay by swapping it with the electric fan relay (working)
- Checked the lambda readings on a code reader (Swings between 200mv-500mv when warm, swings less when cold. Getting a little slow perhaps - will replace)
- Checked the other sensors (Air temp sensor is faulty but unplugging it completely doesn't make any difference. CTS seems fine)
- Replaced the stepper motor (Was having erratic idle issues before, since fixed the problem)
Cheers.