Engine feels stalling when releasing clutch

[JiiHu]

Good to know, something like that tool was used in many youtube videos I hope I'll manage to change it myself and I don't have to go to some repair shop for the job. Though if manifold would have to be removed to change the lambda, it would be perfect opportunity to find 4-2-1 and change it at the same time...

 

[Frank]

I also suspected fuel pump, but the way car gets better on rain, wouldn't seem logical for weak fuel pump or injectors.

At first glance, this seems unlikely. However, when it rains it is almost always in an area of low atmospheric pressure. Like in the shipping forecast when they say 'Severe low expected Rockall, Bailey 0020, etc' - they are not telling you that because low atmos. pressure figures are fascinating, but because they bring rain with them.

Personally, I wouldn't have thought the difference between high and low atmospheric pressure would affect much on a car, but who knows? Certainly anything that has to push against air would have a slightly easier job of it when that pressure was lower, by definition.

 

[Stevecvo]

The MAF apparently reads barometric pressure and so it is possible that a fault in the MAF might be affected by barometric pressure changes. In an article about P0171 faults I came across the following which may be of interest:-

"There is a very effective "truth test" for any Mass Air Flow Sensor. Start the engine, let it idle, and then check the Barometric Pressure reading on the scan tool data. If the reading is about 26.5 Hg and you are close to sea level, you know that you have a defective Air Flow Meter because it is telling you that you are at about 4500 feet above sea level. When the Mass Air Flow Sensor sees this Barometric reading, it adjusts its Air Density table and then "under reports" the actual amount of air entering the engine. It does this because the Barometric Pressure Sensor is actually part of the Mass Air Flow Sensor.

Sometimes the Air Flow Sensor and the sensing wire get covered with dirt, dust, or oil residue, which can also set a P0171. Cleaning the sensor might hold off problems for a while, but eventually, the MAF sensor should be replaced. Always make sure the Air Filter and its enclosure are dirt-, dust-, and oil-free. If you clean and replace the filter and its enclosure as needed, you will prevent the new MAF from failing."

 

[Frank]

The MAF apparently reads barometric pressure and so it is possible that a fault in the MAF might be affected by barometric pressure changes. In an article...

Hi Steve, very good find.

Yeah, that would make sense, the MAF is not actually interested in air flow at all, but in the % of oxygen streaming past in a given time period, so that the fuel/o2 ration can be adjusted further down the line. As the o2 % across a given volume will change with barometric pressure (think mountaineers with oxygen tanks on their backs to remember that) then a MAF/ECU would need to know that.

What made me laugh is that I've actually had a P0171 error code. Tracked it to dirty MAF wire, sprayed it with Contact Cleaner, sorted...and never bothered think what the MAF was actually doing.

 

[JiiHu]

Very interesting text regarding the MAF. I actually just cleaned it again. Last time it was cleaned 30k km ago when it was very dirty, causing car to run lean I changed the filter at the same time now and it was also was very dirty. Definitely made the car a bit smoother, but not sure if it affected positively on the first problem.
I still haven't had time to change the lambda, I hope it would also make the car run smoother. One thing which I also remembered, is that if I have empty tank and I go and top it up, I can clearly notice the car being a bit faster. So maybe this problem is made by multiple parts being old and a bit on their way, such as MAF, fuel pump, lambda, list goes on.., who knows :roll:

 

[tuonokid]

Hi Jiihu
It could also be the idle control valve that needs re-setting to compensate for wear on the engine etc. Basically as there's no adjustable tick over on modern cars like there was on old carburetted cars the ICV takes up the slack by allowing more air in where the car would normally stall as detected by the ECU. Ford main dealers can reset this but you can also do it with Forscan installed on a laptop connected to the ECU with an ELM 327 OBD11 plug in.
Barry

 

[JiiHu]

Thanks for the tip! I have to do it as soon as possible, hope it helps. I will tell how it goes.