Engine stalling after starting issue

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Dawit Tesfaye
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Posts: 8
Joined: Wed Sep 02, 2020 9:35 pm
Drives: Polo iv 1.2 (9N)
Location: Addis Ababa

Engine stalling after starting issue

Post by Dawit Tesfaye »

:( I guss some one will enlighten me with info.
I have polo iv 1.2, 40k (9N) 2004 made and is troubling me by stalling after the engine started and run for couple of seconds. I have replaced fuel filter, checked the fuel pump, relay is okay, ignition coils are okay, spark plugs changed and okay... no idea where to check...
littlepolo
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Joined: Thu Jul 21, 2011 9:47 pm

Re: Engine stalling after starting issue

Post by littlepolo »

That is low mileage for the year. How long have you had the car and was it running fine until now? Any error codes? Sounds like it could be the immobiliser. How is the battery? Maybe disconnect the battery overnight to let the ECU reset then try again. The two things that can help general diagnosis are a scan tool and a classic vacuum gauge. Someone with a better idea will be along soon.
Dawit Tesfaye
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Posts: 8
Joined: Wed Sep 02, 2020 9:35 pm
Drives: Polo iv 1.2 (9N)
Location: Addis Ababa

Re: Engine stalling after starting issue

Post by Dawit Tesfaye »

Thank dear for your suggestions.
It has been two years since I started to drive the car and was running well. I took it to a garage to make a scan and come up with no error codes . It has an immobiliser which is in a good condition. We checked compression and resulted (> 140 per cylinder) which is as goog as new car. We checked the fuel system and is purely functional, no vacuum leaks.

Apparently it cranks, engine starts and stalls on ideling unless backed up with the acceleration pedal. When it stalls, the fuel pump as well as the injectors lose power. So I have to disconnect battry or spark plug fuse to restore power so that it will start again.
Finally the technician decided to back up ECU data (software) and check any faults, however come up with zero fault.

Really no idea what I should do...

Any comment is appreciated..
Thanks
littlepolo
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Re: Engine stalling after starting issue

Post by littlepolo »

Hmm. My next thought is the throttle body (clean, reset/adaptation using VAG/VAGCOM tool) as it can get gummed up, especially around entry of the brake servo. It could also be faulty. Not sure about the fuel pump and injectors losing power - that could be part of the ECU program. I have a 1.4 but have not heard of fuel supply problems being particularly problematic. Not sure if there is anything different for your local climate.
Dawit Tesfaye
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Posts: 8
Joined: Wed Sep 02, 2020 9:35 pm
Drives: Polo iv 1.2 (9N)
Location: Addis Ababa

Re: Engine stalling after starting issue

Post by Dawit Tesfaye »

Hello dear,
Thanks for your input. For your info, we have clean up the throttle body with carb cleaner and jerking idle has gone. So it is working well. Our altitude is about 2300 a.s.l. it has low pressure if it has any effect. But it was well working for more than s year.
I assume that if MAF or coolant temperature sensors are about to fail, the ECU will have a problem to calculate the amount of air/fuel mixture that could affect injection timing which might result too much or too little injection pulse. So engine might stall if injection pulse is low. But what I don't understand is
1. Why the ECU is not recording any related fault.
2. Why engine hesitates to start after stalling by itself.

N.b. I intentionally removed ignition coil and camshaft sensor power socket to see if ECU record error code which it did and confirmed me of functionality.

Now I am confused more...
littlepolo
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Joined: Thu Jul 21, 2011 9:47 pm

Re: Engine stalling after starting issue

Post by littlepolo »

The sensor in the intake is MAP (manifold absolute pressure) and not MAF. Definitely worth cleaning using a suitable spray cleaner. You could also unplug it and try running (if it is missing the ECU goes to a default map -which should get the engine running, although possibly lumpy). Coolant temp sensor more likely to cause problems with hot starting. It could be at fault though. CTS is cheap so maybe worth trying a new one. Not all issues present an error code (dirty MAP and faulty CTS are two examples). Unfortunately, with these old vehicles we sometimes have to swap parts to find the root problem.
Dawit Tesfaye
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Posts: 8
Joined: Wed Sep 02, 2020 9:35 pm
Drives: Polo iv 1.2 (9N)
Location: Addis Ababa

Re: Engine stalling after starting issue

Post by Dawit Tesfaye »

Thanks for the correction (MAP), yes I will swap the CTS and today I have learned that it had some fault codes related to acceleration pedal low signal ( 18041 and 18047) but cleared a while a go. We re scan it to verify and it is not there anymore.
I have read that some one with same fault codes changed the acceleration pedal to clear the code. In my case it is no more present.

My mechanic confirmed me that there is no software problem after backing it up and checking it hopefully. But what I don't agree is that he thought that the hardware (ECU) could be defective. Can the hardware problem specifically affect a single operation if it is defective? I can't believe it...
littlepolo
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Re: Engine stalling after starting issue

Post by littlepolo »

I have heard of problems with the pedal, and potentiometer on drive by wire systems. You should be able to check its operation with VAGCOM (although it might not be conclusive for an intermittent problem).

What is the odometer reading (mls or klms)?
Dawit Tesfaye
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Posts: 8
Joined: Wed Sep 02, 2020 9:35 pm
Drives: Polo iv 1.2 (9N)
Location: Addis Ababa

Re: Engine stalling after starting issue

Post by Dawit Tesfaye »

Dear,
Actually the reading was related to pedal position sensor, and the car is not drive by wire system. However, the PPS doesn't result an intermittent engine stalling. Today I am checking the immobiliser, my guy suggested to reprogram it and is requesting a code. What's weard is the mobil. Light is not appearing at all times. I will keep you posted after today's trial.

Thanks
john M
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Location: Cork

Re: Engine stalling after starting issue

Post by john M »

Have you replaced the crankcase breather valve?.
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