Every Morning, Car Stalls On Acceleration When Idle. Help?

[simba7]

Hi,

As the title suggests, everytime i start my car when left for a few hours, it starts up fine, revs remain between 800-1000 and then as soon as i press the accelerator(still parked), the revs dip so low like it is struggling and then cuts out.

I start the car again and it takes longer to start but does eventually start. I press the accelerator and it stalls again.

The third time i press it, it again takes ages to start up. Once started and idling,i literally press the accelerator FULLY and it again starts to nearly stall.
However as i have pushed it all the way down, it eventually overpowers the stalling from happening and then the car drives fine.


I would like to mention that my MPG is suffering and I have had the Dephaser with the latest revision changed back in 2010.
The problem arose 1-2 years after the dephaser change. Can the dephaser have gone again?

I would GREATLY appreciate anyones help.

Thank You

[AlexB]

Start with checking the temperature sensor and cleaning the throttle body. Are the spark plugs new, what type are they? Was the insulating grease used when changing the spark plugs?

No, it doesn't sound as a dephaser. Speaking of which, when did you change oil the last two times and what oil was used?

[simba7]

Hi Alex,

Where is this sensor located?
Yes spark plugs are Bosche Super 4.

Grease was not used i dont believe.

Thanks

[AlexB]

For the sensor location have a look in the manual. I don't have this engine. It is easier to read it with OBD. When using OBD, please also check the O2 sensors.

The spark plugs may be fine or may be not. Without the insulating grease they begin playing up on cold start, then the coils fail.

You are describing either the effect of a lean mixture (temperature sensor, O2 sensor, dirty throttle body) or the ignition choking. The sensors are easy to check on OBD, the other two require use spanners. The throttle body will actually also show on OBD, although indirectly. I mean reading live data from the sensors.

[simba7]

Hi Alex,

I have since changed the spark plugs twice and the problem has still remained.
The car is fine once it is on the move so I cant really see how it could be the coils or the spark plugs.

I have cleaned the throtlle body already so it isnt that
O2 sensor was changed on the exhaust pipe already unless it is the other O2 Sensor located by the engine.


Air Temperature sensor when disconnected makes no change to the cars performance.

Coolant Temperature sensor havent checked this yet.
Which temperature sensor were you referring to?

Also what happens when the ignition chokes?

[AlexB]

I was referring to the coolant temperature sensor. If it is showing +40C on OBD on a cold morning, then the ECU would mistakenly set the mixture lean. The effect you described is similar to running a lean mixture when cold.

The intake air temperature sensor is not as important, but it is still needed for the calculation of the injection charge.

Regarding the spark plugs. When you open the throttle, the pressure in cylinders increases, and this requires a higher voltage to form a spark. This increased voltage may cause a surface discharge along the coil boot or somewhere else, if dirt or water are present. If you went through several sets of spark plugs without any change, then it is not the cause of the trouble.

O2 sensors. There are two of them, before and after the cat. The upstream sensor is for the engine, and the downstream is for checking the cat. One can check these sensors with OBD.

[simba7]

Hi Alex,

I checked the temperature of the coolant and it was at 10C first thing and the air temp was around 8C so we can rule them out.

The oxygen sensor was fluctuating between 0.078 and 0.670 at idle if i recall correctly, while the other was fixed at around 0.758 or something.

Do these figures look ok?

[AlexB]

Yes, everything is looking good, and the cat is working well.

Did you notice whether the engine stalls due to lean or rich mixture? The same O2 sensors show this. Just step on gas when the engine is cold and look at O2. What about the other sensors? Does MAF make sense? What is the calculated load at idle (this may indicate air leaks or blockage in the throttle body idle system)?

[simba7]

Hi,

I did not notice that however i took screenshots for you.
Please see below

Please see below
Calculated Load
https://s29.postimg.org/6gu8g2pqv/Calculated_Load.jpg

Flow And Pressure Data
https://s29.postimg.org/9jqd5pfbr/Flow_a ... e_Data.jpg

Fuel Trim
https://s29.postimg.org/ejsereac7/Fuel_Trim_Data.jpg

O2 Sensor
https://s29.postimg.org/c3qldjs9j/O2_Sensors.jpg

Temperature Sensor
https://s29.postimg.org/5m33gasif/Temperature_Data.jpg

[AlexB]

I don't quite understand the notions used in this free tool. Does it mean that the long term fuel trim LTFT is +20% or that the mixture is rich, thus causing the trim -20%?

Could you please measure another point, this time on hot engine. The best, of course, it to have continuous diagrams over time... At least two sets of measurements are needed: cold and hot.

On cold engine it is quite normal to have a positive short term fuel trim STFT. Again, I don't understand the notions in the tool. Is it "+" or "-" 59%. If "-", as written in the comment, then it is very strange.

[simba7]

Hi,

I believe it just means "-" means lean and "+" means rich.

Do you only need the fuel trim when hot or all the screenshots?

Thanks

[AlexB]

So, you mean "-" means lean, which is the opposite of the trim, which has to be of a positive polarity to compensate for the measurement. On the other hand, the whole point of listing the trim rather than the O2 measurement, is that the measurement is kept in the sane range by the trim. It is a closed loop control system, indeed!

No, the trim values are not zero on hot engine, but when cold they are much higher. As the engine is not throwing trouble codes, The trim is somehow keeping it alive.

I would be tempted to use a different programme unless you find help on this one.

Merry Christmas meanwhile, chill out, tomorrow is another day!

[simba7]

Hi Alex,

I was driving above 70mph and my engine light started flashing and then went off.

I plugged a diagnostic in and it reported the code p0303 which i believe is cylinder 3 misfire which as i understand could be the coil or spark plugs however i experience no such misfire when driving.

I know what a misfire sounds like as I have disconnected the coils one by one and they all start chugging once i do this indicating they are working.

The sparks were recently changed so I cant see them being at fault.

Nevertheless the sign went out so why did it do this and do you think its related to my problem?

Thanks

[AlexB]

Your OBD results show less than 0.1V (the normal value is 0.45V, the range being 0-1V) on the O2 sensor, which is very-very lean and may cause stalling. The same may indicate misfire, or an injector not working at all, or a vacuum leak. This may cause stalling. Well, your measurements were done on a cold engine, so there is not much can be said about the incident on the motorway...

Interestingly, the long term trim shows abnormally rich, which can be a reaction to the temporary very lean conditions, or an injector issue. This is a long-term average value, and the engine on average is hot. It can be also a false reading due to a faulty sensor.

When you changed the spark plugs, of what colour were they? Was one of them significantly different from the others?

[simba7]

Hi Alex,

There is 1 o2 sensor which alternates fast. Is this the one I should be looking at?

I can try taking a laptop after work and checking the o2 sensor after the journey today.

Also i have ordered 4 Valeo Ignition Coils to see if this fixes the issue.

In my mind i believe it to be the VVT again. But im no expert.