I would check all your 'Earth' points. Ensure all the other cables are connected to the CO pot correctly. Check the pot too, ensure thats operating correctly.

Could possibly be the chip at fault.

Could be helpfull:

To Check the ECT Immerse sensor probe in coolant of specified temperature, and check resistance between terminals.

0 deg C - 8800-102000 Ohms
20 deg C - 35000-40000 Ohms
40 deg C - 15000-17000 Ohms
60 deg C - 7100-8000 Ohms
80 deg C - 3000-4500 Ohms

Could be worth checking you have the correct ACT sensor also. You should have an alloy reducer on the sensor. If you don't thats the wrong one.

To check the ACT sensor:

Measure the resistance between the multiplug terminals
This is fairly difficult, but these are the temperatures/resistance you need to be checking.
0 deg C, 88000 - 102000 Ohms
20 deg C, 35000 - 40000 Ohms
40 deg C, 15000 - 17000 Ohms
60 deg C, 7100 - 8000 Ohms
80 deg C, 3000 - 4500 Ohms

I've also updated the RSBible website so it's a bit more reader friendly, I will add more links and pictures to it over the next couple of weeks. Hopefully that should clear up any problems.

Steve