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R129 SL500 Surge & stall when slowing to halt in heavy traffic

Discussion in 'Engine' started by Johnniek, Mar 30, 2014.

  1. Johnniek

    Johnniek Active Member

    Apr 13, 2012
    Bromley, Kent
    Merc R129 SL500, Audi A6 Avant & Fiat 500
    Dear all

    I wonder if you can help.

    My R129 SL500 has a recurring problem. After a long drive and having been in heavy traffic, it will surge then nearly stall when slowing to a stop. Appears to be when the gearbox down changes from 2nd to 1st (it's a 98 car with 5-sp electronically controlled box & M119 engine) All temps are in range and fans working fine.

    It has recently had a box service (inc fluid / filter / valve body clean) by a specialist along with a full service.

    Prior to this work it had the fault, but to a greater degree whereby it did actually stall once in heavy traffic. In normal conditions the revs dip then recover.. Is this normal? The heat from heavy traffic appear to make this more pronounced.

    I did notice the other day when revving the engine (warm) in park that it misfired slightly, also when the service was done we replaced K&N air filters to stock, could these have caused damage to the MAF?

    Having just trawled the web I noted that a similar problem was fixed by replacing the MAF with a genuine Bosch part,. The MAF was changed last year by a garage when in the hands of the previous owner - any pointers on checking its authenticity? Or any other pointers?

    Thanks in advance :)

    Cheers JK

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