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Polo Mk3 6n AEX 1.4L rough running then no restarting for 10mins


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Hi

 

I would like to ask if anyone could shed any light on the following problem which has been getting worse during the last 6 months.

 

When cold (damp weather too) the car will cold idle badly. 

Driving like this will make it jump/hesitate around 1200-2000rpm any gear. It does not like the accelerator pressed too quickly.  If I drive 2 miles then switch off, it will NOT start again - only turn over.  Leaving it for 10-15mins it will start ok again and then idle & run smoothly.  Again, once the initial problem has gone, the car runs nicely for the rest of the day.

 

The car has new fuel filter (correct one) and new oil separator.

I have tested the imp values of the HT leads and coil pack and all values seem as per std.

Every year I normally remove and clean out the throttle body too with TB cleaner and toothbrush.

Spark plugs seem ok (3 pin Bosch as per Haynes Manual I have bought)

Air filter is new

Sometimes I add injector cleaner to petrol whilst filling up.

 

I can think of the following possibilities but would like to hear from someone with more experience, ....rather than just replacing the list of items below (expensive)

 

1)  injectors ?

2)  coolant temp sensor ?

3)  clean TB again ?  (last time 1yr ago)

4)  coil pack micro crack in plastic case + damp weather ?  (although the car is fine for the rest of the day)

5)  new plugs ?

6)  MAF or air related problem / TB dirty / TB idle control ?

7)  anything else ?

 

I greatly appreciate any constructive tips to resolve this relatively new problem which for the last 8 years had never occurred.

 

Thanks

Phil

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nige8021

First Welcome to the forum.

 

Coolant temp sensor would be my first item to replace, but make sure it's a genuine one as others are of poor quality, the other thing would be the sensor in the distributor, you could also clean the MAP/IAT sensor on the end of the inlet manifold, only use a spray cleaner, do not use a toothbrush as they are quite delicate. 

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Hi. Thanks for your reply.

 

Q. Which one of these would be the most likely due to the fact that it is a very intermittent fault. ?

 

Yesterday these problems were very bad, (the worst I've seen) ....  but today the car started and drove 100% perfectly from cold .... for the whole journey, then restart, and then back home!!  No hesitation, no bad idle, no restart probs whatsoever.  Confused I am !

 

This gen problem occurs prob twice a week

 

Thanks again

 

 

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Hi

Intermittent problems are generally electrical issues.

Push down all the relays you can see and get to.

Clean the earth connections you can get to.

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  • 2 weeks later...

Thanks to those who replied with tips.

 

I believe I have sorted out the problem, but cannot pinpoint which fix actually did the trick.

Convinced it was a "spark" fault (air/spark/fuel), I did the following...

 

1  Took off the coil - put it in a warmish oven for a an hour (to dehumidify?!) then run a bead of silicone sealant wherever I could see any hairline cracks (3!)

2  Took off the dizzy cap and rotor arm, and cleaned all the crud oxide off the rotor arm and 4 contacts in the cap (for each plug), ... back to shiny metal (with 320grit sandpaper)

reassemble

 

Since then (5 days ago) we have had cold, rainy, damp mornings and each time the car starts fine, idles fine, and doesn't die after 5 minutes .... restarting after short trips is also fine, it seems to drive smoother - sparks are most likely stronger.

 

Would still be interested in any comments tho'

 

Cheers

Phil

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I don't have the old-style VW reader for this 1996 Polo - I only have the reader scanner VW/Audi/Skoda Blusmart from Amazon which works with my 2015 Polo.

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13 hours ago, jezisvole said:

Thanks to those who replied with tips.

2  Took off the dizzy cap and rotor arm, and cleaned all the crud oxide off the rotor arm and 4 contacts in the cap (for each plug), ... back to shiny metal (with 320grit sandpaper)

reassemble

Cheers

Phil

Hi

Clean shiny contacts inside the dizzy cap always helps.

One more thing. One day when the engine is nice and hot, take the dizzy cap off and spray WD40 on the inside of the cap. Allow to evaporate and put the cap back on.

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residentmelon

1  Took off the coil - put it in a warmish oven for a an hour (to dehumidify?!) then run a bead of silicone sealant wherever I could see any hairline cracks (3!)

 

I would say buy a new coil or get a second-hand one.

 

Have you took a plug out and checked the spark colour against the block?

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