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1979 450 SL, 144K
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Discussion Starter #1
I recently had the water pump and timing chain on my 1979 450SL replaced. Previously when the car was at operating temperature, it would idle @750 RPM. Now it idles @550 RPM when warm. Is this normal? Should I adjust the idle back to 750 RPM?
 

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'80 450SLC Afro RHD Ikonengold
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2,885 Posts
Your car shoud be K-Jetronik (CIS)
Maybe when pump was replaced mistakenly someone turned the idle screw.
Maybe if parts of idle control were removed for w/pump replacement debris fell in and now aperture is smaller = less rpm.
Maybe warmup idle regulator parts were cleaned (on the top of the pump) and now bimetal operation is more free. If this is the case, after adjusting idle your warmup rpm's will be lower.

After you adjust idle back to recommended, check CO2 levels. They are somewhat connected.
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It's a good idea to fill in your profile with car details so that it is easier to get answear in the future
 

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Djenka018 said:
Your car shoud be K-Jetronik (CIS)
Maybe when pump was replaced mistakenly someone turned the idle screw.
Very possible.
Djenka018}Maybe if parts of idle control were removed for w/pump replacement debris fell in and now aperture is smaller = less rpm.[/quote said:
Less likely, still possible.
Maybe warmup idle regulator parts were cleaned (on the top of the pump) and now bimetal operation is more free. If this is the case, after adjusting idle your warmup rpm's will be lower.
That could happen.

Djenka018 said:
After you adjust idle back to recommended, check CO2 levels. They are somewhat connected.
Check everthing.
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Djenka018 said:
It's a good idea to fill in your profile with car details so that it is easier to get answear in the future
Cause we won't remember that the first question included your car details.
 

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1984 500 SEL euro, 1989 560 SEL, 1980 450 SL, 1981 DeLorean, 2013 F10 BMW
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1,253 Posts
Are you describing the RPM while in gear or while in neutral?
550 RPM while in gear and warmed up is perfect while in neutral the idle should be at 750RPM.

Regards,
 

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1979 450 SL, 144K
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Discussion Starter #5
I'm seeing 550 RPM while in gear. Before the wate pump/timing chaing work, it would idle ~700 in gear. Maybe I'll finally get better than 10 MPG 8).
 

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'79 450 SLC
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456 Posts
If it doesn't feel like its about to die and running smooth then it should be perfect and running better than before. Mine idles at about 550 600 no problem.
 

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'80 450SLC Afro RHD Ikonengold
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2,885 Posts
idle at low will depend on many factors.
My SLC had shaved camshaft (cam lube rail cloged) and years-of-no-drive cloged injectors when I purchased her.
She could hardly idle at 700-800rpm in D. Idle in N was ~900-1000 or she stalls, jerks and jumps.

Nearly new camshafts (original 01/02, no visible marks of wear) and new set of injectors produced purring at 750rpm in N and smooth enough idle of 600-650 in D. After closing/replacing all vacuum leaks and replacing all hoses where fuel mixture passes, she can idle at ~400rpm and she copes with ease (just for test purpose).

And it feels much more powerfull. Way much more.
I believe my problems were most common (power killer) problems.
 

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Always Remembered RIP
1973 450 SLC AMG, 1995 Chevy Tahoe
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Thats funny, but another little thing about the idle in gear I found with everything fine tuned I still and a little problem in D. What cured it was taking out about a 1/3 qt. of over fill from the transmission fl. Cured on first start afterwards.
 

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'80 450SLC Afro RHD Ikonengold
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ussun said:
Thats funny, but another little thing about the idle in gear I found with everything fine tuned I still and a little problem in D. What cured it was taking out about a 1/3 qt. of over fill from the transmission fl. Cured on first start afterwards.
Is there any to take overfill out without a spanner or such tools? Something like to suck it out trough same pipe it came down or...?
 

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Always Remembered RIP
1973 450 SLC AMG, 1995 Chevy Tahoe
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3,381 Posts
standard cyphen about 4 good squezes did me good
but a Vacuum pump/tester. Through the fill tube. sounds better
 
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