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Would running 5w20 affect idle?

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    Would running 5w20 affect idle?

    Would running 5w20 oil affect oil pressure and in turn affect cold engine idle?
    My car idles very low until it is warmed up. I already have a new Temp sensor and soon to follow 02 sensor to see if that clear up the problem, but I just thought about the oil pressure and idle thing this morning?

    Could the oil be too thick, and affecting pressure/idle until it warms up and thins out?
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    #2
    Oil pressure, within limits, won't affect idle. The O2 sensor won't affect cold idle as the engine operates in open loop mode until the engine reaches operating temperature. However, if you have intake leaks, a bad afm, or bad DME temp sensor the engine may not idle properly until the DME switches to closed loop operation. I'd start with a smoke test to find any intake leaks and replace the DME temp sensor.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

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      #3
      I hope you don't have 5w20 in an m20

      that stuff is WAY too thin. Maybe you mean 20w50?
      1989 cirrisblau-metallic 325i

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        #4
        Originally posted by SpecM View Post
        I hope you don't have 5w20 in an m20

        that stuff is WAY too thin. Maybe you mean 20w50?
        Yeah thats what I meant. Sorry, haven't had my coffee at work today.

        Is there a home based kit or method to smoke test?
        Im running a 2 month old miller MAF conversion, so I don't think the MAF is already bad. Will swap in temp sensor this weekend to see if that clears it up.

        What about the heater circuit on the O2 sensor? If that were bad, wouldnt it increase the time it takes the o2 sensor to warm up and the car to switch to closed loop?
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          #5
          I fought a low idle for a while on my M20, ended up being a vacuum leak at the tube under the intake manifold that runs to the block. Replaced one of the o-rings and my idle problems went away. Are you throwing any check engine codes?

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            #6
            Originally posted by Gnarles View Post
            I fought a low idle for a while on my M20, ended up being a vacuum leak at the tube under the intake manifold that runs to the block. Replaced one of the o-rings and my idle problems went away. Are you throwing any check engine codes?
            No CEL. If there are codes, would it trip CEL, or do I have to do stomp test to find out if its throwing codes?

            The reason I think its sensor related, is that it goes away once the cars warmed up. But for the first 10 min, the car idles around 600rpm, and will sometimes stall out, or die if I don't let it warm up before trying to drive.
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