Hesitation when engine cold

[Spirited]

Considering the EGO, the oxygen sensor only becomes active on closed loop engine operation after it has been warmed up. Closed loop operation occures when there is a consistant amount of fuel entering the engine over a given amount of time, such as highway driving where the ECU considers the fuel flow to be as close to constant, where by it is referenced in it's parameters. This means the ECU can carefully regulate the amount of fuel to create a more efficient burn by calculating the amount of fuel combusted in the engine, derived from the exhaust gases where it gathers the air:fuel ratio.

This type of operation as I know only occures in instances of close to no acceleration, so I would think you could almost rule the factor out about the o2 sensor, as you are accelerating when you get the splutter and the car is still warming up.

This brings me to where I think it may be as you say where the air:fuel mix on cold when you start the car up is different to when it is warm, which may be related to how the ECU controls the amount of air taken in by the engine through valves. This may suggest that you do indeed not have a cold start fuel map?

(I still think you may have a cold start fuel map, as the problem didn't occure before that service). Perhaps the parameters of the ECU have changed, the PCV? valve (is that the right one?) has been adjusted or some other factor has caused an incorrect air volume input on idle?

Sometimes when vacuum leaks occur, the engine can run rough, and splutter, even though theory says that the engine rpm should increase due to the amount of increased air volume, but in actual fact, the air fuel ratio has become to far further lean, that less power is produced, due to not enough fuel being present in the volume of air, causing a stuttery idle. When the car is warm, the rpm may increase with a vacuum leak, but this phenomenon of stuttering with theoretically greater air volume does occur on cold starts. I know I am contradicting myself here, but it does happen as the conditions of combustion are different in the engine between when warm and cold as I have experienced in previous cars.

Hope this helps you mate, going by what experience I have.

Look closely into it, only you know your car best, something has caused it - it is just a matter of finding it :)

Goodluck.

Sam.

Edited January 7, 2009 by Spirited

[Simo]

I get this too, car bogs down and wont accelerate for a few seconds, having said that, when Mickey installed my intake both the taylor boys told me this would happen and to warm the car up a bit first.

[spillige]

any one know if its ok to use contact cleaner that has film protection or will this affect the sencore