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77 450SL, 79 450SLC 5.0, 67 250SL, 61 190SL, 61 190, 62 180;Others:www.cardomain.com/id/challenger_7
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30 Posts
Discussion Starter #1
Hello friends.
Can anyone guide me to control the RPM on my car. If I adjust the air screw on top of the engine to get about 1200 RPM on cold start, when the car warms up it will die.
If I adjust the RPM to a comfortable 900 RPM when warm, when cold it will race to a wild 1900 or so.
How can I get a reasonable RPM both when cold and when warm.
Suggestions are highly appreciated.
Cheers
 

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1979 450 SLC 5.0 #677 & 1980 500 SLC #2053
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420 Posts
Hello friends.
Can anyone guide me to control the RPM on my car. If I adjust the air screw on top of the engine to get about 1200 RPM on cold start, when the car warms up it will die.
If I adjust the RPM to a comfortable 900 RPM when warm, when cold it will race to a wild 1900 or so.
How can I get a reasonable RPM both when cold and when warm.
Suggestions are highly appreciated.
Cheers
Sounds like your warm-up regulator is bad. In order to test you need a Bosch fuel pressure tester. You can try finding an old one to see if swapping it out makes a difference. Contact GermanStar in Arizona for a rebuilt unit. They're not too expensive.
 

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77 450SL, 79 450SLC 5.0, 67 250SL, 61 190SL, 61 190, 62 180;Others:www.cardomain.com/id/challenger_7
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30 Posts
Discussion Starter #3
Thank you steve. As I am no expert on this car, just clarifying, the warm up regulator is different from the cold starting unit, right?
The cold starting unit was defective and I had it replaced, so starting from cold is now perfect except, as I explained, it will rev very high and as it warms up the revs start falling down till whatever RPM i have set it at when warm.

By the way notice how close our car VIN # is, just 13 digits difference!

Thanks again
Farouk
 

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420 Posts
Can anyone guide me to control the RPM on my car. If I adjust the air screw on top of the engine to get about 1200 RPM on cold start, when the car warms up it will die.
If I adjust the RPM to a comfortable 900 RPM when warm, when cold it will race to a wild 1900 or so. How can I get a reasonable RPM both when cold and when warm.

The cold starting unit was defective and I had it replaced, so starting from cold is now perfect except, as I explained, it will rev very high and as it warms up the revs start falling down till whatever RPM i have set it at when warm.
The symptoms as you describe them would suggest a defective auxiliary air valve not closing completely which you have tried to compensate via the idle adjusting screw.

I suppose the “cold starting unit” you mention was replaced it was the cold start injector (valve). If the AAV (Auxiliary Air Valve) is defective you have several choices to verify and remedy. You can remove the AAV and test it by putting it in a pan with water and bring close to boiling point. Then try to blow through one of the inlets (put that inlet under cold tap for a few seconds so you don’t swear when blowing). There should be no passage of air. If it proves to be defective you can adjust (compress) the top closing plug of the AAV with a press or a vice to bring the edge of the closing plug flush with the main flange of the body (see pics). Try not damage the brass bulb!!. Obtain a new gasket, it cost $0.90.

Before adjusting the AAV with a press or removing the AAV until you obtain a gasket, you can restrict the throughput of air by inserting a piece of rubber hose (20mm long and 15.8mm external diameter) to reduce both inlet and outlet air passages to about 10mm ID as an interim solution until you obtain either a new AAV (very pricey and scarce) or you adjust the top closing plug. If the hose you find for this purpose is slightly bigger OD than 15.8mm, you take out a wedge lengthwise to reduce to 15.8mm (see pics). This interim solution should balance out your revs at cold start to around 1200 RPM and about 8-900 with engine warm. - Isuspect you might also have an air leak via the contour hoses of the AAV as they become very brittle and replacing them when you sort out the AAV would certanly help. Hope this helps








 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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The EGv107 contains a thread on dis assembly and cleaning of the AAV. Some have been successful in bringing them back to functional.
 

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77 450SL, 79 450SLC 5.0, 67 250SL, 61 190SL, 61 190, 62 180;Others:www.cardomain.com/id/challenger_7
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30 Posts
Discussion Starter #6
Wow, thank you indeed Elrick, I am very grateful for this explanation.
This is the sort of detailed help I am used to at the Ponton webside "IPOG" and did not expect to see that here.
Many thanks buddy, I will give you a feed back when I get a chance to follow your guidance.
Cheers, Farouk
 
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