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My 450sl starts with a very low idle and will increase in speed (to a normal range) when the engine warms up, about 3 minutes later.

The idle is so slow that I have to tap the gas pedal to keep it running.

Reading on this forum it sounds like the idle should initially be at 1500 rpm and there may be some problems with the aux air valve or a vacuum leak? I'm not sure where to look.

Can anyone help with this issue, thank you:)

John
 

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My 450sl starts with a very low idle and will increase in speed (to a normal range) when the engine warms up, about 3 minutes later.

The idle is so slow that I have to tap the gas pedal to keep it running.

Reading on this forum it sounds like the idle should initially be at 1500 rpm and there may be some problems with the aux air valve or a vacuum leak? I'm not sure where to look.
It shouldn't be 1500, that's too high and you'll get weird operation if you try for that. How long have you had that car? Has it always had this while you own it? Or is this something that just started?
 

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It shouldn't be 1500, that's too high and you'll get weird operation if you try for that. How long have you had that car? Has it always had this while you own it? Or is this something that just started?
Scott,
Bluecollar's car is a '73 which means it is an D-Jet EFI model like mine.

My car has high idle speed when started cold , but in a few minutes cuts back to proper idle speed of about 800rpm (now I fixed the leak in the AAV!).

The AAV allows some air to bypass the throttle valve. Result is like keeping your foot slightly on the gas, so engine idles fast. As AAV closes, this air bypass closes and idle should go back to normal if AAV is working properly.

Or, that's the way I understand it!

There should be several links on the net about how D-Jet systems achieve the cold start.

If car does not start at high idle, perhaps the AAV is stuck in closed position or perhaps the cold-start injector is not working?

Checking if injector is receiving power while attempting to start engine would be something to check. The cold start injector acts sort of like a choke on a carb.

The AAV can easily be removed, cleaned and then tested in hot water to see if it opens and closes.

Graham
 

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Scott,
Bluecollar's car is a '73 which means it is an D-Jet EFI model like mine.

My car has high idle speed when started cold , but in a few minutes cuts back to proper idle speed of about 800rpm (now I fixed the leak in the AAV!).

The AAV allows some air to bypass the throttle valve. Result is like keeping your foot slightly on the gas, so engine idles fast. As AAV closes, this air bypass closes and idle should go back to normal if AAV is working properly.

Or, that's the way I understand it!

There should be several links on the net about how D-Jet systems achieve the cold start.

If car does not start at high idle, perhaps the AAV is stuck in closed position or perhaps the cold-start injector is not working?

Checking if injector is receiving power while attempting to start engine would be something to check. The cold start injector acts sort of like a choke on a carb.

The AAV can easily be removed, cleaned and then tested in hot water to see if it opens and closes.

Graham
Sounds correct. Much less complicated than later models of the 107.
 

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Yeah, I'm the one who told you about the AAV, remember? ;)
Yes, and that was very helpful!!

But in this case, we have the opposite problem. Too low an idle speed. 9I had high idle speed)

I was surprised that you did not think cold start idle should be as high as 1500rpm for a minute or two while car warms up. Do the newer cars not do that?

Cheers,

Graham
 

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Not that it's correct, but my car goes to about 1700 cold and sounds like a Cessna 172 on run-up. I know I have work to do on my cold start system, but it has always been in that RPM range when cold.
 

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I was surprised that you did not think cold start idle should be as high as 1500rpm for a minute or two while car warms up. Do the newer cars not do that?
Your car shouldn't, and neither should his, because 1500 rpm is the fuel cutoff number. Just below that is fine. At 1500 or above and you wind up with the magic cycling engine like you had.
 

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Your car shouldn't, and neither should his, because 1500 rpm is the fuel cutoff number. Just below that is fine. At 1500 or above and you wind up with the magic cycling engine like you had.
You are right. My car runs fast, but less than 1500rpm - probably about 1200rpm. I don't think I ever saw 1500rpm idle speed unless I was screwing around!
 
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