zorin:

On your question about a WUR : No, all mixture compensation is done in the ECU. Which brings us to,

Both the ECU and the ignition control unit (EZL) are supplied with coolant temperature information from a dual thermistor (one circuit for the ECU, one for the EZL). Both circuits have the same values and response curves. The unit is located just aft of the ignition distributor; when the plug is disconnected four pins are exposed. Try disconnecting and driving; when disconnected the infinite resistance signals replicate a permanent cold engine condition. If the problem ceases, you will then have to sort out which controller, ECU or EZL, is the culprit.