Cold Idle

[bpossel]

Question... :?:

When my car is just started (cold), the idle is low ~200rpms.

When the car gets close to normal operating temp, the idle jumps up to ~800 and runs very nicely.

Shouldnt the cold idle be higher than the warm idle.  Seems like my baby runs backwards in this case?

Any advice?

Thanks!
Bob

bpossel
Memphis, TN.
1971 280SL
1997 E320

[Naj ✝︎]

Bob,
You may have a stuck cold start valve under the IP thermostat.
This situation does not allow the valve to open up when cold to let the extra air in.
To check, disconnect the air hose on the IP that takes air to the CSV. Start cold and see if that makes a difference.
naj

65 230SL
68 280SL

[bpossel]

Thanks Naj!

I need to raise the housing for this anyway in order to put some permatex on it.  It is leaking a bit of oil....

Should I be able to move the plunger up and down in the housing and see if it's sticking?

Bob

bpossel
Memphis, TN.
1971 280SL
1997 E320

[Naj ✝︎]

Hi, Bob,
Can't remember what the 280 valve looks like.
Here's one on the 230:
Right one in the pix. There's a plunger in the valve body operated by the thermostat. The pin at the bottom pushes on a plate in the pump.
(thermostat on left is from a 280, while the second one is from the 230)
Can you check if yours has this hex nut on the back?

Download Attachment: 230tstat.JPG
46.96 KB

naj

[jeffc280sl]

Hi Bob,

The part Naj is speaking about does not interface with the oil in the engine.  Where do you have oil leaking?

The slide valve in the warmup device is spring loaded and open when the engine is cold.  As the engine warms, engine temp water is circulated through the warm up device on the injection pump.  A temperature sensitive plunger extends as the water warms pushing the slide valve down and choking off the air supply which comes from the injection pump air filter.  If you take the assembly off the car you should be able to manually slide the valve up and down in its shaft.  Let me know if you have any questions.

Jeff C.
1970 280SL 4-speed

[bpossel]

Jeff,

Here is a pic of where I have a small leak, dribble.  Its below the warmup device.
http://www.sl113.org/forums/uploaded/bpossel/200521482547_ip.jpg

Thanks,
Bob

bpossel
Memphis, TN.
1971 280SL
1997 E320

[jeffc280sl]

Bob,

I see where you're talking about now.  The thermostat/heat sensor is mounted in the top half of this unit.  If you have looked at the Haynes Manual in Fig. 3.64 you can see there are compensating washers at the location where you have the leak.  I don't recall any other washers in this location.  Mine does not leak.  Maybe the bolts are not tight enough.

Jeff C.
1970 280SL 4-speed

[Ben]

You need both extra air and extra fuel to raise the idle speed when cold. This device also add extra fuel as the rack is in a forward position when cold and as it heats the plunger shuts off the air valve and withdraws the rack slightly.

You air valve may be free and allowing the air but not enough fuel. The shims where you appear to have the leak are essentially what determines the extra fuel, less shims = less fuel and vice versa. You may eed more shims.

Am I correct on this guys ?

Regards,
Ben in Ireland.
'64 230SL 4sp.

[Shvegel]

After chasing my tail for awhile on the same issue I offer this.
 Try removing the small air filter on top of the pump and see if that helps. I had two of these that had imploded and kept the warmup air from being introduced into the engine

[bpossel]

Thanks All for your advice and suggestions!

I will try all of the suggestions this weekend and post the results.

Thanks again,
Bob

bpossel
Memphis, TN.
1971 280SL
1997 E320

[andy]

i just reassembled my WRD on tusday,after fixing a stuck slide valve,with the help of this site.and after a test run i had a very small leak exactly like yours.i just tightned the two screws down evenly a little more and so far so good.
my symtoms were  my car would not idle cold at all,but would start right up,when i removed the small filter on the side of the pump there was no sucking noise comming from the hole when the engine was cold.this i now know means the slide valve is stuck.
andy.

[bpossel]

I removed the IP air filter and plenty of air was being sucked in. I also removed the housing and applied a very thin layer of permatex on the shims.  This cured the small oil leak.

Here is what is happening....

Now when the car is started (cold), the rpms are at ~500.  When the temp hits ~60C, then the idle jumps to ~1100.  Then when temp hits full normal ~80C, then the idle settles ~900rpms.

Does anyone have any idea on this one?

Thanks,
Bob

bpossel
Memphis, TN.
1971 280SL
1997 E320

[hands_aus]

One of the most important parts of the injection system is the linkages.
It is absolutely imperative that there is NO play in the rod cups and NO lateral movement in the linkage rod across the valve cover.
The venturi must be closed at idle.
No vacuum leaks anywhere.
Then the linkages must be adjusted correctly.
The CSV must not leak.
The air slide valve in the INJ pump must shut off fully when at HOT idle.
The inj pump thermostat can become lazy with age and not operate correctly. 230sl inj pump thermostats are expensive, 250 & 280sl inj pump thermostats are inexpensive.
The igniton system MUST be correct, timing, dwell, correct plugs, leads not shorting, correct impedence etc.Each model has its own method of setting the ignition timing.
When everything is adjusted correctly, then and only then can you adjust the air fuel mixture.
 The info is in the BBB. The CD manuals have info for all models .

Search this site for previous posts on this topic... there have been many.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[bpossel]

Hi Bob Smith,

Thank you for all of the advice and things to check out.  Basically, all of these items have been checked.  The reason I am getting somewhat "picky" about my idle running smooth and normal when cold and hot is that I have even had my IP rebuilt recently.

I am beginning to think that it is an issue with the warm up device.  I will call Hans today and see if he can send me another one.

Thanks again!
Bob

bpossel
Memphis, TN.
1971 280SL
1997 E320

[bpossel]

Update...

I spoke to Hans Utke and he said it sounds like a sticky thermo plunger in the warm up device.  He is going to mail me a new thermo right away.  Of course I will send the old one back to him.  

Will update the site once I receive and replace.
Bob

bpossel
Memphis, TN.
1971 280SL
1997 E320

[hands_aus]

I am surprised that the Inj Pump Thermostat was not tested and replaced (if necessary) as part of the inj pump rebuild.
Rebuilt inJ pump leaking oil?
doesn't seem right to me.




Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[bpossel]

Bob S,

I cant disagree with your comments.  I cant say that I didnt think along the same lines.  BUT, I would still send my pump to Hans if I had to do it over again.  I think that he is a good person and stands behind his work.  Hans truely knows these pumps.  Heck, I just enjoy talking to him on the telephone.  I can relate to him.  My parents immigrated to the USA from Germany in 1950.  Hans reminds me of my Dad, who passed 9 yrs ago.
B.

bpossel
Memphis, TN.
1971 280SL
1997 E320

[Ben]

Bob I had exactly the same symptoms ever since I got my car. I lived with it for a while and it bugged the cr4p out of me so I went through all the checks again. What I found was, and the 230SL is slightly different in this respect, when loosening the 'stat housing it would spring up. This meant that the plunger was already in contact with the slide valve from the word "Go" so I wouldn't have the full benefit of the system.

I added a correc t size washer to this area to lift the 'stat and plunger assembley slightly !

Result !

I now had a car that fires up and idles at 1000RPM and when hot it settles to about 800RPM and is smoother to drive when cold. I verified that the air was shutting off when warm and also gauged the CO when hot and reset the mixture accordingly !

The 280SL is different in this area, I'm not familiar enough but since there are washers for this purpose you may need to add or remove same. Be aware that if your pump was completely redone by and expert, such as Hans, this type of fine tuning still cant be done 'till its back on the car !

Hope that helps and good luck !

Regards,
Ben in Ireland.
'64 230SL 4sp.

[bpossel]

Hi Ben,

Thanks for your post!  I will pay attention to this when I replace the thermo, hopefully this weekend.  If it still doesnt perform correctly, will look at the washer.
Regards,
Bob

bpossel
Memphis, TN.
1971 280SL
1997 E320

[Ben]

No problem Bob but like I tried to point out the 280 is different and I dont believe there is a washer here. I think there are washers further down actually ON the air valve.

Hopefully someone could post a picture of the exact set up differences between early and late cars. All these washers and shims and variants always confused me slightly !

Regards,
Ben in Ireland.
'64 230SL 4sp.

[JPMOSE]

I want to change the IP thermostat on my 250SL since it is the original and they get lazy with age.  I have read through many postings and see that the replacement unit will not seat in the orginal washer (resulting in having to widen the washer).  Does Mercedes (or OEM) not have a later retrofit washer that matches the later thermostat...it seems this would make life easier!  Please advise.

Best Regards,

J. P. Mose
1968 250SL

[Ricardo]

JP
I can't tell you if there is a replacement available, but I can tell you it's not too difficult to alter. The washer is a special shape/dished washer made of aluminum and the hole only needs to be enlarged by approx. 3/32" or so. It helps greatly to have a vice to clamp it into, but you can manage to secure it to a scrap of wood with a couple of wood screws pinching it. If you don't have a vice, you can try stepping up drill sizes a small amount each time and run your drill in reverse, so it doesn't grab the aluminum and spin your washer.Make sure there aren't any burrs that would keep the thermo from seating flat in the washer. You don't want any coolant to get past it and down into the pump. Some like to use a little blue silicone sealant on both surfaces to insure a good seal. Once you have it apart you'll see it's pretty straight forward.....
good luck
Ricardo

[mrfatboy]

I have been going through the exact same problem in the last couple of days.  Check out this thread on the other forum.

http://pagoda113.com/groupee/forums/a/tpc/f/2076001521/m/5551052921

There are plently of checks but I just ended up deciding it was a worn IP.