Author Topic: Polo starts but wont run ?  (Read 6034 times)

Offline maghouse

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Polo starts but wont run ?
« on: January 14, 2010, 11:38:54 AM »
Hi all,

I have a 1997 1.4 POLO ... lovely little car !

But she is playing up

I have had new HT leads, New Distributor cap, new rotor arm, new spark plugs fitted as it had a misfire and this cured the problem fine - runs like a dream

BUT ...

Over the last week or so I am having real problems in starting the car.

It fires first time (even in this icy weather) and revs immediately but then cuts out.

It will do this half dozen times and will finally start - when it is running, it idles fine, runs fine, absolutely no problems at all.

Another BUT ...

It is very intermittent, if you do manage to start the car - if you switch off, it either starts again first time or goes through the half dozen attempts ... really frustrating ....

I thought it might be the battery on a low charge but that seems okay ... if it is the coil (not changed) then surely the car would not run normally once started ? Reading about the 'knock sensor - could this be the cause ?

HELP !  :(

Cristal

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Polo starts but wont run ?
« Reply #1 on: January 14, 2010, 11:58:45 AM »
Hello,

The symptom you describe is exactly what happens if the coded chip in the key isn't recognised by the immobiliser box hidden behind the dashboard (with the factory-fitted immobiliser system).

The code contained in the chip is read by an aerial fitting, which is clipped onto the ignition lock housing, under the plastic steering column trims. I've had problems occasionally with the shielded cables in the aerial lead breaking down, so that even the correct key(s) can't run the engine properly.

A 'knock sensor' detects if the engine is tending to, well, 'knock', and can only do so once the engine is running. I don't think it can shut off the engine. Another problem area is the crankshaft sensor, but a failure there prevents the engine from starting at all, since the engine Ecu can't tell that the engine is turning over.

If there is an O.E. immobiliser, try another aerial & cable; a used one should be alright, since it's only a link between the key and the immobiliser box.

Offline maghouse

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Polo starts but wont run ?
« Reply #2 on: January 14, 2010, 01:07:44 PM »
Hi Cristal. thanks for the reply.

This is an old 1997 Polo - did all Polo's of that age have an OEM immobilser fitted ?

The key seems a pretty standard plastic key (unlike our Sharan which has an 'immobilser key) ...

The only other possibility then is the Polo has an after pro fitted Clifford alarm system which works very well ... maybe that immobilser is faulty ?

Would this be an intermittent fault or a constant problem do you think  ?

Thanks again ...

Cristal

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Polo starts but wont run ?
« Reply #3 on: January 14, 2010, 05:09:12 PM »
Hello again,

The easiest way to check for an O.E. immobiliser is to remove the steering column trims and look for the plastic aerial housing around the head of the key barrel. Or the plastic halves of the key can be split apart along the seam to see if the black chip is hidden inside. If the aerial is present, follow the shielded cable back to the control box, which will be behind the dash somewhere, possibly near the fusebox.

Additional immobilisers tend to break the starter solenoid circuit, so the engine won't turn over (from the ignition lock, anyway).

Offline neo

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Polo starts but wont run ?
« Reply #4 on: January 15, 2010, 07:35:25 PM »
coolant temp sender would be my first guess

Offline maghouse

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Polo starts but wont run ?
« Reply #5 on: January 15, 2010, 07:52:58 PM »
Thanks again Cristal,

Neo - an interesting comment ...

I 'fiddled the day before yesterday and found 2 things - the oil pressure sender and connection were covered in oil so cleaned that up.

I also noticed the temp guage was reading (or not reading) zero ?

Whilst I was fiddling - I made sure all the plugs & connectors I could see were plugged in properly ...

Air Filter back on - hey presto perfect - for the last couple days starts first time and runs like a dream plus starts lovely ... AND the temp guage reads perfect again ? (regret saying this now !)

How can the coolant temp sender affect the starting ?

Offline maghouse

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Polo starts but wont run ?
« Reply #6 on: January 16, 2010, 03:51:43 PM »
Update - SPOKE TO SOON !

Its happening again,

So ...

Changed the keys over to the brand new spare - fires & runs first time ....

Old Key - wont start ...

Has to be that I think I HOPE !!!

Leave it with the new key and see how it goes ...

Wanted - a self healing car please ....

Offline king of the road

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Polo starts but wont run ?
« Reply #7 on: January 16, 2010, 06:40:42 PM »
Hi, your model of polo will have a factory immobilizer fitted, as they started to install them in 1995 (m reg or 10th digit of chassis number is 's' upwards) another thing to consider is the ignition switches on vw's of this era, are problematic. if your fault re appears, then see if the dash lights flicker off when you start the car. you will need to turn and release the ignition key slowly to be able to see if its faulty. the temperature switch is used to tell the ecu how cold/warm the engine is, so it knows how much fuel to give. this also would basically replace the choke system of the kind found on carburettor engined vehicles. hope this helps, dan.

Offline maghouse

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Polo starts but wont run ?
« Reply #8 on: January 17, 2010, 10:30:40 AM »
Cheers for that KOTR ...

Tempted to replace both bits as I cannot work out which could be faulty ...

If the temp sender was faulty - I take it the dash guage would not read so if it does read - gotta be okay ?

Does this just clip in ?   any tricks on replacing it ...

Sussed out the ignition immobiliser sender coil ... looks easy enough to replace - now to find one !

Offline king of the road

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Polo starts but wont run ?
« Reply #9 on: January 17, 2010, 10:53:24 AM »
the coolant temp switch, just unclips, you pull the clip out of the side of the coolant switch housing under the switch, and pull the sender out, careful not to lose the seal off the switch. remove the seal, fit to the new switch, add a little vaseline to the seal, and refit. if the switch has 4 wires going to it, the gauge can work even if the engine doesn't read it right, as it is a dual switch. if its has 2 wires going to it, you need to replace the blue switch, as this one will be for the engine. before you go ahead and replace the immobilizer reader coil, its worth checking the fault memorys of the engine and immobilizer 1st. if the imobilizer is the cause of your problem, then the engine fault memory will have stored in it 'engine control unit blocked.' if its clear of this fault, then its unlikely that the immobilizer is the cause of your issue. best regards, dan.

Offline maghouse

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Polo starts but wont run ?
« Reply #10 on: January 17, 2010, 11:13:01 AM »
Thanks for the advice KOTR - surprised the sender is just clipped in !

I have no access to read the 'memory so will have to do this 'blind as it were ...

The temp gauge has been intermittent before so think that is the place to start !

Will let you know ...

Offline neo

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Polo starts but wont run ?
« Reply #11 on: January 20, 2010, 10:22:24 AM »
One word of advice, go for a genuine temp sender (about £17 (sorry gsf but yours are pants!).
Make sure the engine is cold and remove the expansion tank cap before replacing sender to make sure there is no pressure build up.
If you're quick, can do it with virtually no coolant loss!

Offline maghouse

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Polo starts but wont run ?
« Reply #12 on: February 08, 2010, 08:34:20 AM »
Just an update chaps .... worried this will jinx the car but 'he who dares rodders ...

Car has been running fine so far - nearly 2 weeks without a problem  :D

All I did was unplug the water temp sensor and make sure it fitted okay and took out the ignition immobiliser coil lead and put it back ...

Works perfectly well now ....

Maybe just breaking the contact corrosion ? and moving the lead worked - not very technical I know but seems to have done the trick ...