6n2 1.0 MPI intermittent no throttle response, stalls and then fails to restart

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SebVen1
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Posts: 2
Joined: Sun Dec 13, 2020 1:51 pm
Drives: 2001 6n2 1.0 MPI petrol
Location: Bristol

6n2 1.0 MPI intermittent no throttle response, stalls and then fails to restart

Post by SebVen1 »

I’m going to try to be as descriptive as possible:
My Polo 6n2 1.0 MPI petrol from 2001 quite recently passed the MOT. However in recent weeks it has a habit of stalling at unexpected random moments. This starts with an unresponsive throttle after which the engine stalls and fails to restart, even after the key has been taken out of the ignition and put back in. The alternator seems to work fine and the car tries to start, but the engine keeps on chugging and there is no throttle response at all.

I observed that if the car has been left turned off for a while it does start. But after 20 or so minutes of happy motoring the issue occurs again. Interestingly, it seems that the longer I leave the car turned off the longer I can use it without the issue occurring (e.g. overnight off = 20 min run, 15 min off = 2 min run). However, sometimes days would pass without it starting at all. Additionally, the alternator seems to drain the battery fairly rapidly, which required a jump start on more than one occasion.
“Service INSP” has been showing on the dashboard when the car is running, but not always. There is no fixed time between it showing and the stall happening. It does always show when the car fails to start. No other error lights have lit up.
I got the car diagnosed in the garage and they read out the ECU that showed an error code “65535”. They said that this was an electrical problem most likely with the ECU itself and recommended to have it swapped out, something that they unfortunately couldn’t do themselves. I bought a second hand ECU, which I got cloned from the old one. After installing this, initially everything worked fine. On the first drive, I got to my destination without a hitch, but when I tried to start the car again an hour later, it wouldn’t.

I cannot really detect many other symptoms. On only one occasion did I hear an “electrical hum” after a stall.

The only modification to the car since the last MOT has been the installation of a dash cam which I hard wired to unused ports in the fuse box.

Any advice would be much appreciated. The costs of getting this issue diagnosed and fixed by a garage would be more than the monetary value of the car.
SebVen1
New
Posts: 2
Joined: Sun Dec 13, 2020 1:51 pm
Drives: 2001 6n2 1.0 MPI petrol
Location: Bristol

Re: 6n2 1.0 MPI intermittent no throttle response, stalls and then fails to restart

Post by SebVen1 »

Quick update:
To determine the problem, the mechanic wiped the fault history from the ECU to see if it registers when it occurs again. He also let it run idle for about an hour, which it did without issues. The issue (lose power and throttle response, stall, fail to immediately restart) occurred again after approx 20 minutes when driving the car, however nothing was recorded on the ECU and the readout indicated all systems were 100% fine. Still no closer to finding the fault.
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