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.

Grammabud · #8 12-02-2005, 01:50 PM

Well...there is a warm up regulator listed for the 85. But at that price, I won't R&R the old one just yet.
Many thanks for the advice,
Bud

Benzmeister · #9 12-02-2005, 04:15 PM

pricing around the net sellers, I've explored a few others and Phil is always the best price.
If your car has the Servo ACC system, interestingly this system was originally designed for the Chrysler Imperial back in the 60's and Mercedes bought the patent for it, why I'll never know. If your car is equipped with the heating servo, and it goes, I had mine fixed by Performance Analysis in Tenn,. better then new.

Good luck with the cold idle. I would have it check by a good mechanic who knows these cars, as you can spend a lot of money and in my case it was just a few adjustments and I saved quite a bit of $$ rather then replacing parts. I am lucky the shop I go to with my daily driver a 99 C280 and the project 45SLC, was trained by Mercedes and worked for them for 10 years or so and also BMW trained and worked for them for 5 years. Only downside, he as most smaller one owner two or 3 mechanics can't afford the diagnostic machines you need today but for routine service, suspension work, and even check engine light work, the shop I use is very good and his labor rate is $50 per hour instead of $95 an hour at Mercedes.

ctaylor738 · #10 12-02-2005, 04:38 PM

Are you really saying that your 380 "idles" at 3000 RPM when cold? I am not sure you could put it in gear at that level.

Please verify this, because that RPM is beyond the capability of the electronic idle control to affect and would indicate some bizarre condition like the throttle valve sticking open only when the engine is cold.

BTW - the WUC has nothing to do with idle speed. It controls the mixture, gradually leaning it as the engine warms up.

Grammabud · #11 12-02-2005, 04:48 PM

I have a dear friend from Austria, who lives two hours from us, that was trained by MB in their school at the factory. MB is all he has ever worked on.
He had a double transplant earlier this year and is still recovering. He knows I have this car and is anxious to come play with it, but so far I don't want to worry him until he is stronger. With the accent, I can't understand a word he says on the phone.
Again many thanks for taking time to help me out.

Bud

Benzmeister · #12 12-03-2005, 11:24 PM

Quote:

Originally Posted by ctaylor738

Are you really saying that your 380 "idles" at 3000 RPM when cold? I am not sure you could put it in gear at that level.

Please verify this, because that RPM is beyond the capability of the electronic idle control to affect and would indicate some bizarre condition like the throttle valve sticking open only when the engine is cold.

BTW - the WUC has nothing to do with idle speed. It controls the mixture, gradually leaning it as the engine warms up.

I agree I wouldn't let this go too much longer could, idling that hight especially in the winter on cold start could wreck havoc wiht the engine, the oil couldn't reach the valves that fast?

Grammabud · #13 12-05-2005, 09:54 AM

YES...It idles about 3000 RPM after cold start. I slip it into gear as soon as it catches and hold the brake. That is the only practical way to get it into gear.
I am not driving it in this condition. It is not my daily driver.
Thanks again,
Bud

ctaylor738 · #14 12-06-2005, 08:25 AM

I am trying to figure this one out. The idle speed is controlled electronically by current to the idle valve from the idle relay. More current, less air, lower idle. There is a coolant sensor switch at the back of the engine that, when it opens, will cause the relay to drop the idle from (I think) 900 to 650 RPM. If the whole system shuts down, the valve stays completely open, which allows enough air to keep the engine at about 1200 RPM. The WUC richens the mixture accoring to temperature but does not affect the idle speed, to my knowledge.

So there are two things that could cause this: some sort of binding of the linkage when cold that holds the throttle open, or some giant source of extra air only when cold.

So I guess I would start by making sure that the mechanical linkage is against the stops when the engine is cold, and that nothing is moving when the engine starts. Also that the cruise control is not affecting the throttle linkage in any way.

Grammabud · #15 12-06-2005, 12:34 PM

Thanks Chuck for the idle circuit explanation. Your observations are quite reasonable. I can't look into this until the week end, but will try then.
Just to recap, after the engine warms up it settles down and behaves as it should.
I'm not a novic, just new to MB. I am, littlt by little, learning how the engine management system works thanks to this forum and folks like yourself.
Many thanks again,
Bud

Did you get snow last night? I'm on the eastern shore and we did.