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Fast Idle Not Working Properly
Since I've bought my 1976 230, I've had problems with my fast idle. I have to keep my foot on the gas (when cold starting) until the car warms up before I can drive it without it stalling.
The last Mercedes tech I saw had said to me that there is a problem with the fast idle that causes the car to rev higher until the car is warm, eliminating the need to keep my foot on the gas. Before I take it in to the shop to have this checked out, I'd like some advise on what may be wrong. Since then, I've noticed that my air pump doesn't have a belt running it !!! Hello ! I'm wondering if it is a matter of just attaching a new V-belt to it (providing it works) or will I need to re-adjust the fuel/air mixtures, etc. Sorry for the length. Hope you can shed some light on my problem. Thanks, AARON ROCHARD 1976 230.4 W115 (With Stromberg 175 CD Carb) |
#2
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I have never seen the Stromberg, so I may be FOS, but generally there is a cam attatched to the choke mechanism so that when the choke is closed, the idle is increased. As the choke opens the cam moves to the smaller part and the idle speed is reduced. At some point the regular idle stop takes over.
On the Zenith and Solex, there is a separate adjusting screw for the fast idle. The adjustment process on the Solex is to warm the engine and then move the cam into the position it would be in if the choke were closed and set the idle to 2400-2600 RPM with the adjusting screw. Good luck
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Chuck Taylor Falls Church VA '66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe |
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Thanks for the feedback, actually the Stromberg setup is another monster on it's own. (This I've learned the hard way over the past two years) It works like no other model Mercedes out there, stumping some of the best Mercedes techs. The set up is almost like a hybrid German/English car and has a series of vacuum lines that control everything from the fast idle to the fuel intake. If only there is a slight leak or something is not tweaked properly, everything is completely thrown out of joint.
Don't get me wrong, it has been fairly reliable (for a 25 year old car) but this is just one of the drawbacks to this model. (See transmission problem above) One day when I find the answer to getting this thing running perfectly I'll certainly post it. Thanks, AARON ROCHARD 1976 230.4 W115 |
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Do you have the factory M115 engine manual ? It covers the stromberg in gory detail.
Many people remove the belt on the air pump, to various degrees of success or failure. It's a very american thing to do. -CTH |
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I do have the manual, but I'm not myself that skilled a tech to get the job done. My knowledge, so far, is from observing others and reading the manual. I'm thinking I'd better leave the tweaking to a pro with a stethoscope and tachometer. I would just like to know if the detached air pump has anything to do with the vacuum levels in the system or if I'm barking up the wrong tree here.
Thanks, AARON ROCHARD 1976n 230.4 W115 |
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Good question, but I only work on MBs that predate those pumps, so I don't have any personal experience to share.
-CTH |
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warming up the 230
Hi there. I just picked up a 76 230.4 (European model) for 500 bucks. Runs good once it's warmed up but lags through low gears. Did you figure out the idle problem? Is there a manual available? Any advice you might have would be very helpful. This is the first vehicle I've owned that seems to be worth putting some effort and pennies into and I'd like to do it right.
Thanks, Lon Granger Victoria, BC |
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The Stromberg 175 used on the 220/230 has a starting-fast idle unit on the front of the carb. It serves the same function as an automatic choke. It's a 2 inch round aluminum housing, heated by two water lines. Inside, a bi-metal coil operates a cold starting enrichment valve and a fast idle cam. The cam is connected by a short, adjustable, pushrod to the throttle shaft. Usually the enrichment valve and cam are gummed up/corroded and stuck. You could try a little carb cleaner and attempt to gently work the cam with a small tool, through an axcess hole in the side of the housing. There are kits availible for these carbs.
The air injection pump should have little effect on the idling or fuel mixture as it injects air into the exhaust stream. If the belt has been missing long enough, that pump is probably locked up by now and would be a problem if you live in a region that requires a regular smog test on your car. Happy Motoring, Mark
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DrDKW |
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Thanks. I took the mechanism apart a year ago and found that the small piston that regulates the enrichment was missing a spring underneath that allowed it to give resistance to the coil/rod that pushed on it. Since I put that spring in, it hasn't really given me any problems.
The only thing is that I still have to warm up the car for a few minutes before I can drive it, otherwise it stalls at a stop. Is this normal ? Or should I be able to drive away without keeping my foot on the gas ? Aaron Rochard 1976 230 W115 |
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That same mechanism also operates a stepped, fast idle cam inside the housing, connected to a short adjustable pushrod linked to the throttle. If it's not stuck the either the bi-metal housing cover or the pushrod needs adjustment.
Happy Motoring, Mark
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DrDKW |
#11
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Thanks, I saw that, but didn't know what to do with it, so I left it alone (amateur over here) The mercedes mechanic I took it to said it had something to do with vacuum. My car has no vacuum pump on it, but I don't believe my model year (1976) needs one, as the automatic brakes work fine.
Thanks for your advice and I'll mention it to the next tech I take it to. Maybe I need to go to a mechanic more familiar with the Stromberg, not necessarily Mercedes. Aaron Rochard. |
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