I am trying to solve a problem with my Mk1 1.6 petrol Focus.

The engine is not running smoothly and feels down on power.

I know that it is not the coil pack as this failed and was replaced a few months back and the current problem is nowhere near as severe but still annoying.

If I disconnect the battery to reset the ECU the problem disappears for approximately 20-30 minutes before coming back. There are no warning lights illuminated on the dashboard.

I suspect it could be a faulty sensor that is giving an incorrect reading as the ECU "learns" resulting in an incorrect fuel/air mixture.

Any suggestions?

[quote name='ralphrj' date='08 October 2010 - 01:31 PM' timestamp='1286540479' post='100259']
I am trying to solve a problem with my Mk1 1.6 petrol Focus.

The engine is not running smoothly and feels down on power.

I know that it is not the coil pack as this failed and was replaced a few months back and the current problem is nowhere near as severe but still annoying.

If I disconnect the battery to reset the ECU the problem disappears for approximately 20-30 minutes before coming back. There are no warning lights illuminated on the dashboard.

I suspect it could be a faulty sensor that is giving an incorrect reading as the ECU "learns" resulting in an incorrect fuel/air mixture.

Any suggestions?
[/quote]

with these issues its best to take it to a garage who can read the live readings on a diagnostic so they can pinpoint the issue really it can be a split in a hose causing an air leak it cam be that the coil was replaced but the misfiring has damaged the cat a fauklty lead choked fuel filter to name a few it could be the exhaust o2 sensors really a diagnostic will save you money in the long run that way you only replace what is found to be faulty and not half a dozen parts in the hope one of them fixes it