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Thread: Polo only runs smooth with oil cap removed...Help please!

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  1. Polo only runs smooth with oil cap removed...Help please! 
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    Hi folks

    So my daughter has a 2006 Polo 1.4 16v (bky engine) automatic it idles and runs rough all the time I replaced the map and checked for vacuum leaks but this didn't help
    It idles rough then after a 100miles or so the engine light comes on and it gives a too lean code which is why I replaced the MAP sensor

    The bizzare thing is it only runs smooth when you remove the filler cap, there is some negative crankcase pressure that you can feel when you lift off the cap. As soon as you put the cap back on it runs rough again.

    There is a one way valve on the cam cover that feeds into the left side of the airbox I would have thought was a breather for the engine but its direction of flow is into the engine not out.....could this be faulty?

    Any ideas?

    All help appreciated
     
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  2. Re: Polo only runs smooth with oil cap removed...Help please! 
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    To start with the throttle body needs careful cleaning after being removed and then the unit reset to the ECU in Basic Settings 060 after clearing the learnt values in Adaptation 10 and then the EGR valve must be re-matched in Basic Settings 074 and tested in 075, the EGR valve is what usually causes this problem, after the codes have been cleared and the clue is the MAP sensor fault which does not go away after a new sensor.
    Anthropogenic climate change, the biggest con inflicted on mankind since religion...

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  3. Re: Polo only runs smooth with oil cap removed...Help please! 
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    Cheers crasher I'll give the throttle body a clean although it was done only 5k-ish ago and then re-calibrate as you said
    There is no EGR on this model

    Don't suppose you could tell me how removing the the oil cap makes the engine run smooth again?
    Also what is the purpose of the vacuum valve on the cam cover that feeds to the air box, I could understand it if it flowed engine to air box but it goes the opposite way?

    Thanks for your help, I'll let ya know how I get on
     
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  4. Re: Polo only runs smooth with oil cap removed...Help please! 
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    I didn't see it was a 2006, the pre 2006 BKY had an EGR valve. It is a positive crankcase ventilation system of a closed circuit design where the fumes in the crankcase are mixed with filtered air and then drawn into the engine and the system is regulated by a diaphragm valve. Removing the cap making it run better suggests an air leak or a failed breather valve in the breather unit (036 103 464 AH) on the back of the engine, but a dirty and mall adjusted throttle body scan give the symptom of an air leak on engines that do not have an Air Mass Meter where they rely on a MAP sensor measuring inlet manifold depression. We fit the Febi replacement breather unit which we sell at £43.68 inc VAT, they are £99.94 genuine.

    Anthropogenic climate change, the biggest con inflicted on mankind since religion...

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  5. Re: Polo only runs smooth with oil cap removed...Help please! 
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    I replaced that breather abot 5k ago when I fitted a replacement engine

    Other info that maybe useful for diagnosis:

    The engine I fitted was a BBY engine from a seat ibiza with 55k on the clock and it had an egr but just blanked it at the engine port also fitted all the bky ancillaires on it.

    I also emptied no1 cat as the car was very sluggish and I suspected the cat. Car ran great after so my suspicions were right.

    One of the things that cafuffles me is that there is negative crankcase pressure

    Could you also tell me what the purpose of the vacuum valve on the cam cover is as mine seems to allow air into the engine not out??

    I've got the week off next week so will try an sort it out
     
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  6. Re: Polo only runs smooth with oil cap removed...Help please! 
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    The cam cover valves bleeds filtered air into the engine to mix with crankcase fumes which are then ingested through the breather valve into the inlet manifold. Take off the crankacase vent convoluted pipe on the back of the inlet manifold and plug the manifold allowing the crank case fumes to vent to attmophere temporarily. If this makes it run well I would say the check valve in the breather has failed. I am a bit concerned helping you going further than getting it running well until you restore the cat system to correct function, I get a bit aggrieved at people removing mandatory emmisions control systems. I now retro fit fuel tank and exhaust emission treatment systems to the custom cars I build.
    Anthropogenic climate change, the biggest con inflicted on mankind since religion...

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  7. Re: Polo only runs smooth with oil cap removed...Help please! 
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    Thanks for the info Crasher

    I removed the pipe as suggested but it made no difference unfortunately.
    I swapped all the coil packs for a spare set I have. made no difference
    I did the same with a spare set of injectors..... no difference
    I also swapped the valve in the cam cover for another spare one I had and also cleaned the evap purge valve (dunno why it was just a hunch). The car ran better for sometime afterwards but then after a few miles it just reverted back to running rough although not as bad as previously.

    I guess I'll just have to try something else. Till I get to the bottom of the rough running

    I can't find any vacuum leak but planning on changing the inlet manifold for the spare bby manifold I have, I'll just blank the egr port
    I've got a spare knock sensor too somewhere so will change that over just to rule it out.

    I hear your concerns about the no1 cat but the reason I removed it is the car wouldn't go over 45mph, once emptied the car drove fine and pulled as it should and I don't have the spare cash to buy another cat and the no2 cat seems to keep it running clean enough to get it through emissions OK.

    I appreciate that you may not want to advise me anymore with the cat being removed and thanks for the advice so far.
     
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  8. Re: Polo only runs smooth with oil cap removed...Help please! 
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    That the removal of the starter cat made it better is a symptom, have you done a compression test?
    Anthropogenic climate change, the biggest con inflicted on mankind since religion...

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  9. Re: Polo only runs smooth with oil cap removed...Help please! 
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    sorry i thought id replied to this
    Turned out the be the pre cat lambda sensor
    Thanks for your help
     
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