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accelerating wildly up and down!! S70 1998

Afternoon guys!

On start up my 98 S70 accelerates wildly up(about 1500 rpm)and down for about 30 seconds then settles down and is normal. This happened about 3 months ago for about a day or two and it quit. I thought maybe it was bad gas since it went away but now it's starting to do it again. Any thoughts on the problem???

Thanks!

Henry

82-260gle, 84-240gl, 85-740gle, 91-740, 92-940gl, 97-850, 98-S70








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    accelerating wildly up and down!! S70 1998

    Any codes stored in the computer? If not, I would start by unplugging the mass airflow sensor (you will likely throw a check engine light doing this, so be prepared to reset) and see if it idles normally. My Buick 'hunted' for idle & i had to keep my foot on the gas to keep it running when its MAF went; the Volvo just wouldn't stay running, so I guess any number of weird occurrences can happen. You may also want to check for vacuum leaks, turbo lines (if it's a turbo), etc. When's the last time you changed spark plugs?








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      accelerating wildly up and down!! S70 1998

      No codes stored in the computer. I'll try the MAF first since I now vaguely remember that happening to my first 240gl. I'll also try the vacuum lines and it's not a turbo and my plugs and wiring only have 3k miles on them. Thanks for the info and jogging my memory.

      H








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        accelerating wildly up and down!! S70 1998

        Don't forget, never unplug/plug in the MAF with the ignition on. Tends to mess up other things, like the ECU.

        It does sould like you are getting unmetered air in when the engine is cold. Look around the vacuum tree for leaks. Also check the intake manifold gasket for leaks.

        Klaus
        --
        Proud owner of a 1967 220S








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          accelerating wildly up and down!! S70 1998

          Did check all vacuum lines and might have had a bad one leading into the intake manifold right on top of the fan. It looked cracked and brittle but I couldn't tell if it was ripped or not but I changed it anyway. Did remove the MAF completely and blew some air through it (gently) to possibly dislodge any debris that might have been stuck in there. Put it all back together and the engine is REALLY smooth now!!

          Thanks to both of you for the info.

          Henry







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