High RPM Idle

[chezjoey]

See revised post!!!

[chezjoey]

After 25 years I started my 1970 280SL but not without quite a bit of preparation. One caveat, the engine is a 280SE. The fuel tank was cleaned of old fuel and filter changed, the fuel pump and hoses changed, the fuel lines purged, the spark plugs changed, the ignition checked, etc. After a lot of cranking she fired up. I was pleased.

The problem is the engine idle speed is high, 3,500 RPM. I followed the Linkage Tour and adjusted the linkage. Both venture and IP stops sit perfectly. The manifold large screw was adjusted clockwise and counter clockwise with no change. The IP thumb screw (engine stopped) was adjusted 2 clicks counter clockwise and 2 clicks clockwise. This increased the RPM'S. I didn't use the vacuum gauge because I felt it would help me fine tune and not help getting the RPM,s from 3,500 to 700.

In checking I found two things which lowered the RPM. The first, by removing the air hose from the air filter and capping it with my thumb the idle speed came way down. The other was disconnecting the pump rod linkage and moving the IP to high speed controlled the RPM.

Can anyone give me some ideas how to proceed?

[ctaylor738]

Are you sure you are seeing 3500 rpm?  That's way beyond "idle" and I don't think it's possible to get that rpm with the throttle plate closed.

Anyway.  You say that the throttle body lever and the pump lever are both on their stops.  But have you checked that the throttle plate is actually closed when the adjusting screw is on the stop?

Next thing to check is to see if the slide in the warm running device is moving freely, and that the thermostat is working.  Lots of posts and information in the Technical Manual about how to check this.

I suspect that your WRD is stuck in the full rich position which is allowing lots of air and fuel to the engine even with the pump lever on its stop.  This may be aggravated by by the throttle plate not being fully closed.

Good luck,

CT

[Frank Mallory]

You've got an air intake leak from a rubber fitting or gasket somewhere in the intake tract It probably dried and shrank from age and non-use. You'll find it, congrats on getting it going!

[chezjoey]

Thanks Guys,
If my tack is correct the RPM is 3.500. I checked, the throtle plate. It is fully closed. The WRD may be the problem. I will check it and the thermostat tomorrow. There may also be leaking gaskets as Frank surmises. I will check that also.
Having not moved for 25 years could there be a problem with the IP that would cause the high RPM?
Joe

[jaymanek]

Too much fuel requires a lot more air for it to be able to rev to 3500... I would think its one of the suggestions above..

[garymand]

Wow, a good one.   "The first, by removing the air hose from the air filter and capping it with my thumb the idle speed came way down."
Hmm, That hose goes to the large air scew.  You should be able to close that screw and get the same effect.  Close it down to get the same effect.  

But that is just the air.  And the fact that is getting enough air through that hose to idle at 3500 is a puzzle: How did the screw get screwed out that far?  are you saying it was running fine when put to bed 25 years ago?  You didn't have this problem back then?  I can't understand how the air is getting through that hose unless the screw is wide open... 

But that issue isn't your real problem: The fuel is controlled separately by the FIP so I can say for sure, you have a lot of extra gas coming in.  I'm just curious about the air and how the idle air valve got screwed out far enough to give you 3500rpm idle.  

Is all or most of the extra air coming in through that hose?  If you break the linkage and open the air buttler fly how much more air can it take?  

Yopu need to find out where the gas is coming in from: cold start valve?  Warmup valve stuck down (but that would give you plenty of air too so there would be no need to breath more air through the idle air valve),  finally the rack.  

Make sure the cold start valve is closed and not leaking or on all the time.  Check the warmup valve is closing off the air, you can back off the screws and see if it is working right.  Take it off and boil it: watch the pin retract.  

"The other was disconnecting the pump rod linkage and moving the IP to high speed controlled the RPM. "  This is not very specific, lacking detail of exactly what you are doing.  Do you mean "when I pushed the rod down lightly a few mm, the rpms dropped"?  That would be helpful.  If that is what you mean, it just says that adding more gas exceeds available air so the rpms drop.  Godd if thjat is true close down a lot of the air from the idle crew and then figure out where the gas is coming in from.  
  

[chezjoey]

I began with Chucks suggestion to check the WRD. It was stuck so I took it apart siliconed the cylinder and piston and tested the thermostat in hot water. With the WRD working fine now it was re-installed. The car started with no change in the high RPM.
Now I am following Gary and Frank's suggestions. I turned the air large screw to the closed position and blew into the air hose (engine off). Not much but some air still passed. Started the engine and the RPM's were lower. Again placing my thumb over the hose reduced the RPM's to just over 2,000. I agree that air is entering from somewhere so my next step will be to replace all of the old hoses. I'll report back when the hoes are replaced.
Answering your question Gary, the car ran fine when I drove it to the shipyard in Puerto Rico and again from the shipyard in New Jersey to Connecticut. I believe the problems began when a body shop had the car for a few months (working gratis to repay a favor). When I got the car back it had to be towed home. My mistake.......
Joe

[kampala]

Joe,

A couple of points may be worth considering.  Firstly, I will advise that I am also learning these cars and my suggestions are based on what I have learned and tried -- am no expert.


1. 280SE engine can be factory installed and correct for a LATE 280sl.  Unless you know it's been changed, you can check your numbers as it may be factory.  If you search the forum and tech manual, you find this info.

2. If your car is a USA version and its a Late 280sl and it still has the vacuum retard distributor ---  you need to check the vacuum line from the air intake to the Two-Way-Valve.   The two-way-valve will control when your distributor has timing retarded or not.  Typically, at idle your timing will be retarded via this vacuum.  If the line is disconnected, or broken, or the Two Way Valve is not doing it's job, your timing will not be retarded and your idle would increase as you describe.  To test, you can run the vacuum line directly from the air intake to the distributor, by passing the two way valve.  This vacuum would retard the timing.  Pull the vacuum line and idle would go up.  If this test brings down the idle, you know where to start attacking the problem.   

If you are not sure what vacuum line I am describing, follow the line from the distributor as it connects to the two-way-valve and then connects to the air intake on the right side (when facing forward). 

3. If your car is an Automatic, you should also check that the dash-pot on the left side and below the venturi is not pushing the venturi open upon starting the car. 

Good luck ...

[ja17]

Good advise from kampala, You  have a huge amount of extra air entering the engine somewhere to have an idle this high. Check the vacuum line going to the brake booster. Yes do check to make sure that the intake venture valve is not being held open by the vacuum dash-pot if you have one on your engine.  Make sure that the set screw on the venture intake is set correctly (linkage tour). Still sounds like the WRD.  Make sure that the "heat feeler" is cutting off the extra idle air. Take the small air cleaner off the WRD after the engine is warm and plug the opening with your thumb to see if the heat feeler is closing the air passage.

[chezjoey]

Thank Oz & Joe for your help.
First some history. My company sent me to Puerto Rico, for 3 months, in 1965. As it turned out the stay lasted 23 years. The 280SL was purchased from a dentist, we lived in the same condo. Because getting parts for the MB were difficult, the dentist's mechanic convinced him to remove the MB engine and replace it with a Ford. I got the car with the Ford engine. I purchased a used MB engine in NY and had it shipped to PR. Unfortunately, not knowing an better, the junk yard sold me An SE not an SL engine. We exchanged engines. Therefore, I have a US car but not a factory SE engine.
Distributor vacuum tubing is dry as is the booster pump vacuum tubing. Replacements for both are on order. The dashpot is clear of the venturi stop and venturi in completely closed. With engine running venturi pulls a little air.
I want to remove the WRD filter but I haven't got a wrench thin enough to fit the nut. I am trying to locate one. Any suggestions?
Joe

[Garry]

Hi Joe,

The question that comes to mind is how you established tht you have a sedan engine and not an SL engine? What you may well want to do first is establish exactly what engine you have in there.  Have you had a read of the Tech manual on engine numbers and markings as sometimes it can be confusing for beginners to work out what engine you have as some of the head casting numbers can confuse, especally the SE/A designations cast into heads on later SL engines.
http://www.sl113.org/wiki/Engine/CylinderHead

Garry

[chezjoey]

Garry, Your reply left me with many doubts. I don't know much about the engine I have the tech manual and the forum are all I have been reading but they are confusing at times. The engine seems to have all the bells & whistles that the SL engine has. I considered trying to get an SL engine but I quickly put that thought to rest. I will stay with my SE engine for now if I can.
The engine is marked 280SE/A. The number on the head is 130 016 08 01. Both numbers are in the tech manual engine table. What else should Iook for to convince myself it is a compatible engine? Thanks.
Joe

[66andBlue]

Joe,
look for the engine number on the block below the spark plugs as shown in the photo here:
http://www.sl113.org/wiki/DataCard/EngineNumber
If it is a 130.983 xxx then you have one for a 280SL but if it is a 130.980 xxx then it is a 280SE engine

[jaymanek]

My 1969 car has an original matchin numbers engine marked SE so it may well be correct

[chezjoey]

My motor no. is 130 983 12  008326 (what I thought was 17 was actually a 12).
I contacted Tom Hanson of the Classic Center. Here is his reply and I quote,

"Hi Joe,
Yes, this is for sure the correct series replacement engine. It’s at least from 1970. 2nd version 130.983 engine. You should be ok. The “17” in the middle of the engine number is actually a 12. That designates automatic transmission. 280SE/A is the “general” type for this series engine. Keep me in mind when you need parts for it."

I am thankful to learn I installed a correct MB engine.
Now let's resolve the high idle problem. Still waiting for replacement hoses to arrive. Also, have not found wrench narrow enough to remove the WRD air filter.
Thanks all for you input.
Joe



 
 

[Garry]

Well Joe, really good news on that front,

Just that bit of correct information well and truely paid for your Group membership for a few years and Tom is always so helpful

Garry

Membership Administrator
Other than Americas

[Bonnyboy]

Isn't the wrench for the WRD air filter one of those skinny wrenches      check this out:    

 http://www.sl113.org/forums/index.php?topic=20334.0

Local bicycle shop should have one.   Only $11.00 up here in Canada for most sizes - I bought a whole set minus 23mm last week for $25.00.

[chezjoey]

Unbelievable Garry, Tom sent me that response in less than 15 minutes from the time I emailed him.
Thanks Bonnyboy, I read the posts regarding the thin 23mm wrench. I clicked the bicycle shop link and ordered a Park Tool cone wrench for $14.01 including shipping.
Joe

[glenn]

Hi, Your engine is getting enough gas(and air) to turn 3500 rpm at idle-TOO much.  It requires about 1/4 to 1/5 that(and air) to turn 750 rpm.  You have to find where all this gas is coming from.   It is either coming from the CSV or the FIP (or a secret source)?.  Check the CSV by plugging it.  The FIP is either the rack rotated too much (by the stop adjustment-shade tree guy) or the atmos pressure/WRD lever.   Take the WRD off and push down on the lever.  (Assuming the rack is moving freely-take off cap and screw in the 5mm bolt)