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2007 ML 350, 2000 Corvette, 1969 Yenko Camaro
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58 Posts
Discussion Starter #1
I picked up my newly bought 380sl 69k miles today. Previously it ran fine, I test drove it for a few miles the week before.
When I got in it to drive home it was running on 7 cylinders, bad miss and white smoke coming out the exhaust. After about 10 miles it ran smooth again but still idles rough. The previous owner hasn't driven it much lately.
I drove it about 1 hour home on the highway at 70mph. It ran perfect but still idled rough. It seems to smooth out just off idle. I can creep along at 2mph and it feels smooth. It has great, smooth pickup, no sign of the miss.
Any help is greatly appreciated.
Thanks
JZ
 

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Registered
1981 380 SLC
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20 Posts
I have the exact same issue with mine (1981 380 SLC) and I am in the process of working out what it is. Others will no doubt have better input than I, however at present I believe I have a major vacuum leak. The reason I believe this that the economy gauge currently sits in the middle on idle (and should be pinned to the left) if yours does the same perhaps you have a similar issue....
 

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Registered
2007 ML 350, 2000 Corvette, 1969 Yenko Camaro
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58 Posts
Discussion Starter #3
thanks killer

Thanks for the support.
I know old chevy engines by heart but I have a lot to learn about these Benz engines. I'd like to fix this issue without going to the local Benz dealership and paying $100/hour labor.
Any suggestions Guys?
Thanks
JZ
 

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Premium Member
2010 Mercury Milan Hybrid, 1993 BMW 325i convertible
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6,077 Posts
You've dropped two clues about it:

1) The car sat for a while
2) It smooths out just above idle

You've got a vacuum leak. These engines are very sensitive to unmetered air. Get yourself (if you don't already have one) a hand vacuum pump and start tracing out vacuum circuits. Replace everything that doesn't hold a solid vacuum. On my car even some of the hoses that looked perfect were leaking, and then 2 years later the ones I hadn't replaced started to leak. I wound up completely replumbing the car with all new hose, and it hasn't given me a problem since.
 

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Registered
2007 ML 350, 2000 Corvette, 1969 Yenko Camaro
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58 Posts
Discussion Starter #5
Thanks Scott

I have a nice hand vacuum pump and as soon as it gets above 25 degrees and the wind goes below 30mph here in wonderful central Pa. I'll start tracing out all vac lines. GOD I hate winter!!!!

Guess I'l just fire up the propane heater in the garage.
Thanks for the great tip.
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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32,353 Posts
An "Italian tuneup" might also help. Fill it full of premium and some Techron first.
 

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Registered
2007 ML 350, 2000 Corvette, 1969 Yenko Camaro
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58 Posts
Discussion Starter #7
My first thought too

I dumped some Lucas fuel injector cleaner/top end lube in and filled with premium. I'll drive a little more today to run it thru.
 

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Registered
2007 ML 350, 2000 Corvette, 1969 Yenko Camaro
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58 Posts
Discussion Starter #8
Just drove it cold

Drove the 380 cold this morning. It still runs on 7 cylinders throughout the rpm range. It does go away only after it gets well into operating temp. Then has the rough idle.
 

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Registered
1984 380sl
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81 Posts
rough idle

I have a similar problem with my '84 380sl. The idle is rough , but acts more like it skips a "beat". The dash ecomnomy guage in the reads ok , it's pinned to the left. The idle sits at about 500rpm and it has died on me while sitting at a traffic signal a couple of times. Plugs were replaced about 5000 miles ago and this problem never showed up until after I had the timing chain & guides replaced. Is it just too slow an idle or are there any other ideas out there. Could be a vacumn leak but I believe that that would show up on the dash guage. Maybe not?? Anymore ideas out there? Thanks for all help.

Ben, Scottsdale,AZ 1984 380sl.
 

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Registered
2007 ML 350, 2000 Corvette, 1969 Yenko Camaro
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58 Posts
Discussion Starter #10
one good thing

I thought this Benz engine was going to be a very strange engine for me. I rebuilt an old VW rabbit engine about 2 years ago. This 3.8 is very similar and works on the same basic design with the fuel dist block, injectors, seals and modules etc. Can't wait til it warms up a bit around here so I can tear into this possible vacuum leak/rough idle stuff.
 
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