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    Thread: Rough Idling on my Zen MPFI

    1. #1
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      Rough Idling on my Zen MPFI

      Bought a second hand 2003 Zen MPFI with about 70K on the odo. Got a full service done at a MASS center as soon as I took delivery. There is just one issue I'm trying to get to the root of.

      The idling of the car is pretty rough once the engine heats up. The idling is perfectly smooth when I start it up in the morning, but once I've drive for a few minutes, it becomes rough. I do give it a minute to come up to operating temperature before I start off BTW.

      When I say rough, I mean a lot of vibration, specially in the steering column. It feels a little bit like sitting in an old bus(ok, slight exaggeration there, but you get the point). Please note that the idling speed itself seems to be fine and fairly constant, its just the vibes. All of this is with the AC off.

      Took it back to MASS and they told me its normal. But I don't believe that. They just don't want to take the trouble to figure it out. I'll probably try with an independent mechanic next, but wanted to get some ideas before I do that.

      I did look under the bonnet to see if I could spot something obviously wrong, but honestly couldn't. Spent some time searching different forums and these seem to be a few potential causes.

      1) Engine mounts gone bad
      Not sure how to check these. But I'm thinking I'd notice some issues when driving as well if the mounts had gone bad. But will check them out.

      2) Sensor malfunction
      This is the most likely issue in my mind, but having some trouble bypassing the system to generate the codes. The rubber housing is fused to the metal on which its mounted, and don't want to prise it apart without a replacement in hand. Will do this over the weekend.

      3) Fuel system issues
      Probably look at this last because I don't even know where to start.

      4) Bad plug
      If a plug had gone bad, I should be seeing the issue when the engine is cold as well. But worth checking out. Got all the plugs replaced with the service so they're all new.

      5) Belt tension
      Does it even make sense worrying about this? Can it lead to vibes?

      I am going to look at each one to try and eliminate the problem. But I wanted to run this by GH to see if anyone has had a similar experience, and if they did, what the issue ultimately turned out to be. I'm only getting started in terms of understanding engine mechanics, so my own experience is quite limited.

    2. #2
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      mclaren1885's Avatar
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      Engine and gearbox mounts would be first on my list of must check. If you are having vibrations in the steering column, obviously there are some vibrations that are being transmitted from somewhere in the engine bay.

      Could be a busted steering rack/column as well.

      I am assuming you do not have a RPM meter to check if the rpm is constant or keeps fluctuating? If you can hear the engine rev up and down by its own, probably the cam/crank position sensor is busted.

    3. #3
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      when your engine and O2 sensor heat up the ECU goes to closed loop and stops fueling rich. and that is when you notice these issues. could you try disconnecting the O2 sensor temporarily and see if there is still vibration after you engine warms up?

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      Quote Originally Posted by mclaren1885 View Post
      Could be a busted steering rack/column as well.
      I had asked MASS to specifically check this out, and they came back saying it was fine. But will add this to my list of things to do.


      Quote Originally Posted by mclaren1885 View Post
      I am assuming you do not have a RPM meter to check if the rpm is constant or keeps fluctuating? If you can hear the engine rev up and down by its own, probably the cam/crank position sensor is busted.
      No, don't have a RPM meter. At least the variations in revs is not large enough for me to be able to tell with just my ears.

      Quote Originally Posted by 007 View Post
      could you try disconnecting the O2 sensor temporarily and see if there is still vibration after you engine warms up?
      Will try this out and report on what happens.

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      Does your car have a power steering? (My knowledge on Maruti cars is as good as ABCD to an illitrate, so pardon me for that stupid question)

      If it does have power sterring, check if the oil is more than the minimum level. This at times causes issues.


      Cheers!

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      Another common problem can be a leak from a manifold. Once hot this may be sealing itself (if not totally then somewhat more).
      Drive carefully, the life you save may be your own.
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      Quote Originally Posted by obsessedbyfiat View Post
      Does your car have a power steering? (My knowledge on Maruti cars is as good as ABCD to an illitrate, so pardon me for that stupid question)

      If it does have power sterring, check if the oil is more than the minimum level. This at times causes issues.
      No, its the base Lx model. Call me odd, but I specifically wanted the non PS model. Heard some negative things about it being too numb.

      Quote Originally Posted by sgiitk View Post
      Another common problem can be a leak from a manifold. Once hot this may be sealing itself (if not totally then somewhat more).
      Thanks. I'll add this to the list as well. There is a greasy bit around the manifold, but I figured that was just the mechanics at MASS being untidy.

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      Quote Originally Posted by woolf View Post
      There is a greasy bit around the manifold, but I figured that was just the mechanics at MASS being untidy.
      Let me take that back. A leaky manifold is not going to manifest itself with oil residue. There is no easy way to tell isn't it? Visually it looks fine while the engine is running. No apparent signs of gases leaking or any sucking sound. Maybe I'll tighten the nuts once to be on the safe side.

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