380SL high idle after cold start - PeachParts Mercedes-Benz Forum

Grammabud · #1 12-01-2005, 10:31 AM

Hi everyone, I am a new member with an old 380SL. It is an 85 with 230K miles. It was a gift, I think. After removing several bushels of pine needles and evicting the ant colony, it seems to be in unmolested condition. With about 30 miles of test running, everything seems to be in OK order.
My initial question is regarding the high idle condition after a cold start. It starts immediatly, (hot or cold) but idles very high (about 3000) when cold. As the engine worms up, the idle gradually reduces to a normal speed. Is this normal? Any advice will be most appreciated.
Many thanks in advance,
Grammabud

Walrus · #2 12-01-2005, 11:28 AM

Hi and Welcome...

Have you searched these fora? High idle has been discussed in numerous posts, which can be found by searching, using high idle as search criteria...

Good luck with your quest.

Benzmeister · #3 12-02-2005, 10:05 AM

Quote:

Originally Posted by Grammabud

Hi everyone, I am a new member with an old 380SL. It is an 85 with 230K miles. It was a gift, I think. After removing several bushels of pine needles and evicting the ant colony, it seems to be in unmolested condition. With about 30 miles of test running, everything seems to be in OK order.
My initial question is regarding the high idle condition after a cold start. It starts immediatly, (hot or cold) but idles very high (about 3000) when cold. As the engine worms up, the idle gradually reduces to a normal speed. Is this normal? Any advice will be most appreciated.
Many thanks in advance,
Grammabud

I had the same problem with my project car a 79 450SLC, the Mercedes shop I took it to, did a couple of things. The tightened and adjusted the throttle linkage, as it was ready to fall off. the adjusted the air fuel mix and CO2 mix and fixed a couple of vacuum leaks. Now it is fine. But the first thought the mechanic had was the cold idle valve, which is usually the culprit. Your car is a muich later model and might have a computer module that controls all of this. So, I would recommed taking it to a good Mercedes shop which has diagnostic equipment or a dealer, As most private shop can't usually don't havethe proper diagnotic equipment and try and fix it the old way, replacing parts, so in the long run a dealer will probably be cheaper?

halman2228 · #4 12-02-2005, 12:46 PM

What rpm do you have at warm idle? I may get corrected here, but "normal" warm idle should be 750ish.

If you have normal warm idle, I believe it would point in the direction of warm up regulator problem (if so equipped) and/or whatever else controls cold idle speed.

If this describes your situation, search "warm up regulator" before you dive into the "high idle" search (high idle is so common, you'll get a gajillion threads to sort through and could grow old getting through all of them).

My invoice ($.02) to follow...

Good luck
Kevin

halman2228 · #5 12-02-2005, 12:47 PM

to mention my cold idle speed is only about 1200.

Kevin

Grammabud · #6 12-02-2005, 12:58 PM

Warm idle is 700-800. I will look into warm up reg.
Many thanks,
Bud

Benzmeister · #7 12-02-2005, 01:12 PM

sits on top of the engine next to the idle control screw, got to the Fastlane on this site and see if there is a warm up regulartor avaiable for your car, if not then the whole warm idle is controlled by a computer, which from pics I have see is located under the drivers seat. I had a 85 Porsche 911 and for some reason the Germans put these, now crude computer controls under the drivers seat, if there is a box under there it is probably the computer. I looked in the factory service manual for the engine, but it only cover the M116 and M117 up to 1980. The other two factory manual cover other sytems up to 85. So I have to conclude there were some major changes in engine management after 1980.