High Low Rev at start 1972 280se 4.5 - Mercedes-Benz Forum

 
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post #1 of 9 (permalink) Old 04-03-2014, 09:52 AM Thread Starter
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High Low Rev at start 1972 280se 4.5

I have learned that pictures lie and believe none of what you read!

Last May I bought the "Rags to Riches" MB on ebay. I drove it til November when it wasn't in the shop. It is now back on the road for another summer of tweaking. I have replaced lots of stuff, starter, steering linkage, fuel pump, major tune up etc, and more to come.

My issue is when I start it to warm it up, it revs really high, drops down low, revs high and so on. Then suddenly it's fine. If I put it in drive it does not happen. Since I have a driveway between my neighbor and I, the noise can be an issue at 7am.

The other question would be my idle, too high and the car bolts when put in Drive, too low and it stalls.

I have a very nice inexpensive local mechanic I like, but it's new to him too.
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post #2 of 9 (permalink) Old 04-03-2014, 10:24 AM
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common problem , when the idle reach a certain rpm , the fuel shut off kicks in , then as the engine roll to a stop , the shut off goes away , and you run again . the real fix is to replace the air slide valve , or put a restrictor in the hose to it to slow down the air flow .
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post #3 of 9 (permalink) Old 04-03-2014, 12:36 PM Thread Starter
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Air slide valve?

Do you mean Air Slide Auxilary Idle Valve?
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post #4 of 9 (permalink) Old 04-03-2014, 12:40 PM
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Yes... the Auxiliary Idle Valve. These often get stuck. Also, check for any air/vacuum leaks that may contribute to this issue. Old and/or cracked hoses, etc.
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post #5 of 9 (permalink) Old 04-03-2014, 12:44 PM Thread Starter
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thanks

Could what my mechanic calls a rotted radiator have anything to do with air intake?
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post #6 of 9 (permalink) Old 04-03-2014, 10:52 PM
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Could it be the coolant temp sensor? I had a similar thing happen to me on another vehicle. Just a thought.
John.
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post #7 of 9 (permalink) Old 04-04-2014, 08:16 PM
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My brother-in-law's 107 did that as well. Hit the aux air slide with a brass hammer and it changed. Bottom line, I replaced the aux. air valve. FIXED!
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post #8 of 9 (permalink) Old 05-16-2014, 09:15 AM Thread Starter
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FIXED!

It was the wrong spark plugs according to my friends at European Auto Solutions in Waltham MA. I get my baby back next week!
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post #9 of 9 (permalink) Old 05-16-2014, 10:42 AM
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I hope that fixes it, but not sure why it would. See what else they can tell you and also report back how you are doing with it. Happy motoring! : )
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