Stalling In An Auto

[turbofreak6111]

Ok so im new here but i need some help from somebody here. I am working on an a 280sl that belongs to a good friend of my grandmas. It has a hard start up at first but runs fine when it is started. also i am having troubles with it stalling with sitting there at idle in Drive, Reverse, 2nd, and 3rd; but neutral and park it runs just fine. im thinking that it just needs some new fluids because it has 33000 miles on it and the guy last changed the oil about a year ago since her rarely drives the car. im thinking of just draining the tranny fluid, changing the oil, and put some new coolant in it as well. i was hoping if i could get some more insite on my problem i have here and hope that somebody else has experienced this problem as well. i appreciate the help and suggestions.

[twistedtree]

There is a solenoid that should be activated when the car is placed in gear, and it inches the throttle linkage up a bit to maintain engine RPM compensating for the transmission load.  It's usually right on top of the manifold where the linkage rod cross over.  It's probably not working, or needs adjusting.  Check fuses first, and check with a test light to see if it's getting power and getting grounded when in gear.  There are two pressure switches on the trans which provide the grounding.

[Jonny B]

The solenoid on top of the manifold may not be hooked up. I am not sure if it is on all 280 SLs but the solenoid on top of the manifold was used with A/C cars to do just as twisted tree indicates. On automatic cars without A/C there is a vacuum dashpot mounted by the intake to the throttle body that helps with the idle set up. The manifold may still be mounted there but not hooked up (this is the set up on my 280 SL, which does not have A/C).

[Markbhai]

I had the same problem with my 230.  It was the solenoid with mine.  It was just badly adjusted.  Effectively it wasnt increasing the throttle revs as it was touching the levers.

[tel76]

The solenoid on top of the manifold may not be hooked up. I am not sure if it is on all 280 SLs but the solenoid on top of the manifold was used with A/C cars to do just as twisted tree indicates. On automatic cars without A/C there is a vacuum dashpot mounted by the intake to the throttle body that helps with the idle set up. The manifold may still be mounted there but not hooked up (this is the set up on my 280 SL, which does not have A/C).

On automatic cars without A/C the solenoid on the inlet manifold was used (at least it is  fitted on my 1968  280sl ).

[Jonny B]

I don't know when the solenoid stopped being connected on non A/C cars. As I typed, on my 1970 280 SL, the solenoid is there, it is just not connected. My car VIN is 12730.

[Naj ✝︎]

 on my 1970 280 SL, the solenoid is there, it is just not connected. My car VIN is 12730.

Hi, Jon,

When was your car actually made?

0147xx was Nov 69.

Lot of differences on the very late cars as Tom Collitt can confirm.

Naj

[Jonny B]

Per the listing in the technical manual, my car was produced sometime in September of 1969.

[Cees Klumper]

My non-AC car was made in June 69, and has the solenoid (also affectionately known as the CSS- Constant Speed Solenoid) and I think you'd need something to help the engine idle in automatics, if you don't have the CSS, and it would need to be pretty strong to move the linkages.

[Jonny B]

In preparing a summary of the various editions of Pagoda Notes (to be posted separately) I read through an earlier discussion about setting the throttle linkages (Touring with Joe). In that article is indicated that it was US spec cars without A/C that had the CSS fitted but not hooked up (using the dashpot at the throttle body inlet) and in 1970 cars, cars with A/C did have the CSS wired. There was no fixed cut off number given.

[turbofreak6111]

the one im working on is a 1970 280sl. where is the solenoid located again

[turbofreak6111]

also do you have any pictures

[ja17]

The Constant Speed Solenoid is attached to the intake manifold and influences the linkage. (see "The Linkage Tour").  It was used on automatic transmission cars pre 1970 and also used on all A/C cars from 1970.  The hydraulic switches on the auto tranmission activate the CSS.  The device is meant to keep the idle at a constant rpm when set in drive or reverse gear.

Most often other factors are the cause of the engine stalling. An inoperative CSS will normally just allow the engine to drop off to a lower rpm, but continue to run in most cases.  

I suggest that you check the basic tune-up settings, check the WRD on the injection pump, check the air filter on the injection pump, read "the linkage tour" and check the linkages and venturi valve etc first.  When the engine idles smoothly at 700 rpm in park warm, then set the CIS to boost the idle in drive back to 700rpms.

If you cannot achieve a perfectly smooth idle check the compression of the engine.

[Shvegel]

Also on the top of the transmission is a 3 way solenoid that is connected to the transmission by a linkage that changes the control pressure of the transmission so it doesn't drag as hard in neutral. It is common that the linkage will get sticky when these cars sit. Lift up the carpet on the passenger side of the transmission tunnel and you will see an oval cover. You can access it through there and see if it is moving freely.

[twistedtree]

Also on the top of the transmission is a 3 way solenoid that is connected to the transmission by a linkage that changes the control pressure of the transmission so it doesn't drag as hard in neutral. It is common that the linkage will get sticky when these cars sit. Lift up the carpet on the passenger side of the transmission tunnel and you will see an oval cover. You can access it through there and see if it is moving freely.

Have you found this to change the loading on the engine?  In my very limited experience getting one of the 3-position solenoids adjusted properly is that it makes a big difference in how firmly the transmissions shifts, but little to no difference in engine loading, i.e. the engine loading is the same no matter what position the solenoid is in.

[Shvegel]

twistedtree,
I never tried it. I just know there is a neutral position that effects the pressure. I was told it was to keep it from dragging.