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  #1  
Old 08-17-2003, 10:23 PM
afmcorp's Avatar
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Join Date: Jan 2002
Location: NW Indiana LaPorte
Posts: 571
72 350sl funny idle where to start

hello

well the 72 is now running starts right up and all systems go. but... it has a funny idle. when first started the rpm goes up then rapidly down up down up down and so on. after a drive it seems to stop.

now it did this the very first day we bought it. we drove it and it seem to stop didn't any problems on a 1500 mile drive. so this issue is not from it sitting for 2 years.

any body got any ideas?

it also seems to run extremely rich now. alot of black smoke comes from the pipes on start up. makes me think something in the choke is not right.

tks for any help
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Thanks Much!
Craig

1972 350sl Red/Blk 117k
1988 420sel charcoal/Blk 140k
1987 420sel gold/tan 128k
See My Cars at:http://mysite.verizon.net/res0aytj/index.html

Pound it to fit then Paint it to match!

There is only First Place and Varying degrees of last!

Old age and deceit will overcome Youth and Enthusiasm every time!

Putting the square peg in the round hole is not hard... IF you do it fast enough!

Old enough to know better but stupid enough to do it anyway!
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  #2  
Old 08-18-2003, 11:02 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
Craig:

You don't have a choke, you have D-Jetronic fuel injection.

Several possible causes, most likely rich running (hence the black smoke).

Several possibilities here

-- bad ignition (plugs, wires, points (yes, you do have points), cap, rotor.

-- bad connection on the air temp sensor in the air intake horn (check for bad wires or a poor connection, or an open thermistor).

--bad MAP sensor, causing serious rich running. Can only be tested for resistance of the two windings, but the usually failure is the anaeroid inside goes bad and it no longer responds to pressure changes.

-- bad temp sensor or bad thermo-time switch for the cold start valve.

If it blows black smoke at full throttle, you need to have the mixture checked. If it cannot be set, check the temp sensors, and if they are good, you will have to replace the MAP.

I'd also run a bottle of Techron or RedLine injector cleaner through it, especially if it has been sitting undriven much -- this will clear the injectors and fuel pump. Don't start "fixing" things until you run the injector leaner and a couple tanks of fresh premium thorugh it!

Peter

c
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #3  
Old 08-19-2003, 01:43 AM
afmcorp's Avatar
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Join Date: Jan 2002
Location: NW Indiana LaPorte
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techron

hello peter

thanks for the guidance. it has sat for 2 years in my garage waiting for me to take it for a drive. it was running just fine the 3 or 4 times i moved it in and out of the garage during that time. so a couple of months ago i went to move it and it wouldn't start. looked like a weak or poor spark. so i started replacing primary wire and the resistors. after that it started just fine. but went to this high low rpm and belching black smoke. seemed to calm down once it warmed a little.

it needs to get cleaned out with new gas. on the techron where can i get this brand. i seem to remember chevron sold it but we don't have chevron around here.

i know one thing is clear. it needs a tank full of premium gas and some good injector cleaner.

any advice is greatly appreciated.

tks
craig
__________________
Thanks Much!
Craig

1972 350sl Red/Blk 117k
1988 420sel charcoal/Blk 140k
1987 420sel gold/tan 128k
See My Cars at:http://mysite.verizon.net/res0aytj/index.html

Pound it to fit then Paint it to match!

There is only First Place and Varying degrees of last!

Old age and deceit will overcome Youth and Enthusiasm every time!

Putting the square peg in the round hole is not hard... IF you do it fast enough!

Old enough to know better but stupid enough to do it anyway!
Reply With Quote
  #4  
Old 08-20-2003, 08:50 PM
Registered User
 
Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
Craig:

Techron fuel injector cleaner is sold in many auto parts stores, even the low-rent chain ones.

You almost certainly have bad gas in there, and it will take a while to get the plugs clear once they get sooty. If they are Bosch, get the fuel system clean by running a fresh tank though with Techron in it, then replace the plugs. They recover from carbon fouling VERY slowly (except the Platinums).

Peter
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #5  
Old 08-21-2003, 01:35 AM
afmcorp's Avatar
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Join Date: Jan 2002
Location: NW Indiana LaPorte
Posts: 571
techron

Peter

i did just that. i went to chevron's website and learned it was available at advance auto so i stopped there today and picked up 2 bottles.

i am going for a drive this weekend ( i have promised this to myself even if i do nothing else all weekend) and will be using new hi test gas and techron. thought i would put the 20 gal bottle in about 7 gals. run this out then use 1 bottle to a fill up.

i know one other thing is that a bunch of the wiring to sensors (especially the horn in air cleaner) could use some new wire. you can see insulation flaking off and you can also see discoloration/corrosion on the exposed wire. but it's over 30 years old so actually it's in super shape.

tks
craig
__________________
Thanks Much!
Craig

1972 350sl Red/Blk 117k
1988 420sel charcoal/Blk 140k
1987 420sel gold/tan 128k
See My Cars at:http://mysite.verizon.net/res0aytj/index.html

Pound it to fit then Paint it to match!

There is only First Place and Varying degrees of last!

Old age and deceit will overcome Youth and Enthusiasm every time!

Putting the square peg in the round hole is not hard... IF you do it fast enough!

Old enough to know better but stupid enough to do it anyway!
Reply With Quote
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