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Rough engine behaviour...

  • 26-01-2010 4:21pm
    #1
    tmcw
    Closed Accounts Posts: 396 ✭✭


    Just looking for some suggestions for things to check/eliminate/opinions on a 15 year old 1.4 petrol Cordoba (VW) engine.

    Engine runs a bit rough at lower rpm, between 1000-2500 rpm, feels a bit "jumpy". At dual carriageway/motorway speeds, the engine is a lot smoother, like it normally is. I was looking at it at the weekend while stationary, and revving it up quickly from low idle (about 750 rpm) to about 1500 rpm or above, it sounded a bit "skittery", like it was loosing power, or not firing on all chambers, but getting there eventually. Now if I did it gradually, the "skitter" wouldn't be as obvious, but still felt a bit rough, if you know what I mean. Previously if I did the same thing, revving quickly, it would be smooth, no matter how quickly I pushed the accelerator in.

    I had it looked at last week by a garage, and they did some tests and "adjustments" and said that it was running better, but I haven't honestly noticed a difference. I did about 150 miles over the weekend, and fuel economy seems to be like normal (though majority of that was at carriageway/motorway speeds when the engine "feels" smoother; maybe I'll get different results about town).

    Some details: spark plugs, leads, distributor cap and rotor were renewed about 15 months ago (maybe 7k miles ago). Car had a few (maybe 5 or 6) difficult starts over the cold spell (spark plug fouling?) but is starting fine now. Air filter is about 1 year (maybe 5K miles).

    Now, there was a bit of coolant loss recently, I was expecting possibly head gasket, but garage tests showed they think it's ok (they did compression test on coolant system, and checked the expansion tank on analyser for exhaust gasses). The coolant temperature housing was seen to be leaking, and was replaced; that at least seems to be fixed - regularly checking the level for the next couple of weeks on that. I was initially thinking coolant leak through gasket into cylinders, fouling spark plugs, but from what I've read, this would usually be accompanied with lots of constant white steam from the exhaust as well. Now there is a little bit of white plumes initally, but no more than most cars I see, both new and old, and in this weather, not to be unexpected, and it usually clears after a few minutes good driving. Exhaust doesn't smell sweet or petrolly either.

    Any suggestions on what to try/check/look at next?


Comments

  • #2
    AzureAuto
    Banned (with Prison Access) Posts: 233 ✭✭AzureAuto


    Is it carburettor or fuel injectted?
    If carb, have the second stage needle replaced/cleaned out.
    If fuel injected, remoe them and send them to be ultrasoically cleaned, you could find somewere that does this online.
    Aternatively, check all vacuum and breather hoses are clear of "mayonnaise" and blockages and that the PCV valve (postitive crankcase ventilation valve is clear and doing its job. Other than that, providing a compreeion test doesnt show anyhing untoward, id be looking at HT leads or the other components in the igntion system a little more closely.


  • #3
    tmcw
    Closed Accounts Posts: 396 ✭✭tmcw


    AzureAuto wrote: »
    Is it carburettor or fuel injectted?
    If carb, have the second stage needle replaced/cleaned out.
    If fuel injected, remoe them and send them to be ultrasoically cleaned, you could find somewere that does this online.
    Aternatively, check all vacuum and breather hoses are clear of "mayonnaise" and blockages and that the PCV valve (postitive crankcase ventilation valve is clear and doing its job. Other than that, providing a compreeion test doesnt show anyhing untoward, id be looking at HT leads or the other components in the igntion system a little more closely.

    Thanks for the reply.

    Engine is fuel injected. Will get out the Haynes manual to find out what the second stage needle is. Is it in the airbox, or further down the throttle body? I have access to ultrasonic baths at work, and could borrow one. What would be best to use in the bath? Have access to all sorts of chemicals/solvents too.

    Cleaned a pipe from crankcase to airbox recently, had yellowy-white "mayo" in it. Noticed that the vacuum pipe connection to air inlet (I think it switches a butterfly valve between cold air in and hot air from exhaust shroud) seems a bit dodgy. Connection is like a fabric tube, connecting the plastic tube (from airbox) to the air inlet. Sometimes looks like it's pinched. Could I replace this with something else appropriate? Again, at work I have access to all sorts of tubing.


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