M130 idle quality

[wwheeler]

How smooth should the idle be for a '68 M130 motor @ 800 RPM? I have had my car for only a year and am not familar with Mercedes until now. My engine has a little twitching but maintains a steady RPM at idle. It runs VERY smooth at higher RPMs. I have done an extensive amount of work regarding tuning-up and linkage adjusting, so I think everything obvious has been covered.

It may be that the factory high output, high compression 6 cyl. engine typically has a little shake at idle. Just wanting to know what is normal so I don't drive myself crazy.

[mdsalemi]

Wallace,

Once warm, my idle is smooth as silk...however if I let it continue to idle, it will get a little rough.  Then, as soon as there is a high-speed blast (the proverbial Italian Tune Up) it is back to smooth.

[wwheeler]

Thanks for the reply Michael,

I think my car was dormant for so long from the PO, that some of the idle issues are related to inactivity. I think it may take a few good high speed runs to solve that. One of the hardest things to adjust to on these cars is that they MUST be driven. Consider it part of preventative maintenence if you will.

[wwheeler]

I am still trying to resolve the idle quality on my M130 280 SE engine.

I now have a new fuel pump (old one went out) and have rebuilt the cold start valve. The Injection pump has been checked at all ranges and just the idle is too rich. If I lean the low range mixture thumb screw on the pump enough to lean the mixture at idle, then the engine stumbles from a standing start (too lean). It runs great once the rpms are above 1800.

The rebuilt CSV leaks out the hole with the small hex bolt about one drop every 4-10 seconds with the pump on and the engine not running. I think that is too much and is giving me the extra fuel to make my idle rich. The rebuilder on the East coast claims that is normal. Another person on the West coast said that they all leak some even if you rebuild them and that much may be more than normal.

What do you guys think? Is that much leakage enough to cause the rich idle mixture. If not, what else could be giving me the rich mixture only at idle? ( I have checked the WRD and it is OK).

For people who have had their CSV rebuilt, is the leak completely gone after the rebuild?   

Thank you for your input!

[jameshoward]

Wallace,

I have a 230 not a 280, but after my FI pump was re-done the idle hunted up and down. I did the linkage tour a few times and then it just hit a sweet spot. I too had to tinker a lot with the FI pump idle mixture screw, but I did it in conjunction with the idle adjustment on the inlet manifold. The adjustments were very minor, but it's sorted and the idle is steady as a rock at about 700-750 ish both cold and hot. I attribute this to doing everything in the linkage tour a few times until it worked. I also did all the prep, such as points, dewll, gap, plugs, valve clearance etc first. It's definately an art not a science given the mnay variables in play. I'd recommend you stick with it and tinker a bit more. FYI, my car has quite low but uniform compression; all below about 120psi. It doesn't give me any problems.

JH

[Cees Klumper]

The idle on my 280 SL is very smooth, although I keep it a tad above the recommended 800 RPM. No shaking. Only recently, it has started to run a bit rough between the time the WRD cuts out and when the engine is really at operating temp (need to work that one out) but, once warm, the idle is very even indeed.

[ja17]

Hello Wallace,

When all is well, you can literally set a full wine glass on the motor at idle without spilling anything.

If you are concerned that your CSV is an issue, simply block the fuel line off to diagnose the issue.  If it fixes the idle problem, then you found it. Otherwise keep on looking.

Some things to check if the CSV proves not to be the problem. Compression must be nearly even  (within 5-7%) or you are wasting your time. A compression problem will manifest itself in an uneven idle, long before other more obvious symptoms show up.

Use an ohm meter and check the plug wires and ends for a weak link.

Try pulling the spark plug leads, one at a time with the engine running to isolate a problem. (naturally use special insulated or plastic pliers).  If you find a problem with one particular cylinder, try movint it's injector or spark plug to another cylinder to see if the problem moves.

Try the split linkage CO test with the car  at idle in gear running (someone insiide the car with foot on brake) If you can make the idle smooth by splitting the linkage and checking mixture, then you still have an idle mixture issue.

Good luck,

Joe

[J. Huber]

Any time I follow Joe A. with a post I am inclined to say -- "what He said..." so

What he said...

However, in addition, my engine used to jiggle a bit at idle but it turns out it was not the idle so much as the motor mounts. After I replaced them, things smoothed out.

BTW, I have my idle a little higher as well. Just stays smoother.

[wwheeler]

Thanks for the great thoughts guys! Here are some questions:
Linkage - When I use the 10 mm guide pin method, the IP rod always ends up being 231.3 mm (with machinist's calipers). I have checked it several times and it is always the same. Is this OK or should I set it right at 233 mm? I don't know why the two methods don't jive.

CSV - I will plug the line and test. Great Idea.

Compression - I have tested before and found #4 cylinder to be 8% lower. I will retest. Test with engine warm, all plugs pulled (anything else?) What do you do if they are not equal?

Engine mounts - Never thought about that one. How do you confirm they are bad?

Plug wires are brand new solid core, injectors maybe. Engine/ IP was rebuilt not long ago by PO. Don't know everything that was done.

[ja17]

Hello Wallace,

The 233mm length is a basis for setting up correct linkage.  It is not exteremely critical to get the exact 233mm. You are most likely close enough.  It is most important that the venturi is closing all the way when the injection pump lever is on it's rest stop. If the rod is close to the 233mm length then your linkages will have the correct geometry. When the linkage geometry is correct. The linkages at the venturi and the injection pump will be in the correct position to meter air and fuel. In addition the accelerator pedal and its linkages can be adjusted for correct transmission function and correct throttle travel.  Correct linkage geometry allows the minor adjustments of the air screw, and idle mixture thumb screw to functtion correctly.

If you are familiar with the split linkage CO test (Blacklick CO meter) try it at idle with engine in gear (another person in car with foot on brake) to see if you can smooth the idle out. If you are  not familiar with the test let us know.

Sounds like you have covered most of the basics. James has a good suggestion, if you have not checked your motor mounts do so. They can make an amazing difference in drivability ans smoothness.

To check the mounts, examine them closely. If the centers are "punched loose" from the rubber surrounds, then  the engine is basically sitting on the subframe (metal to metal).

Good luck, sounds like you are on track.

[wwheeler]

Thanks Joe,

As you know, all mechanical things have tolerances. It was driving me crazy that the two linkage adjusting methods weren't yielding the same result. It is nice to know that there is a little give on the 233 mm dimension. Incidentally, the venturi is closed and in fact when opening, sticks just a bit at first. I think it should be OK.

I have never tried the split linkage when the engine is in gear and at idle. Just out of curiosity, what effect does it have versus being in neutral and at idle? Should I just check to see if the mixture is correct or should I actually set the pump screw and air screw at this time?

I have lots to do....

[glenn]

Smooth idle---  An old Jefferson nickel should stand on the oil cap.

[ja17]

Wallace, when the linkages are split and engine at idle in gear (someone holding brake on), try advancing each split linkage just a bit,  one at a time. See if either one smoothes out the idle.

[wwheeler]

First test with the CSV fuel line disconnected and plugged was revealing.

With the CSV operative:
- Starts well, runs very rich at cold high idle (partly due to worn WRD thermostat). With engine warm, high and medium range mixture is right on. Low range is slightly lean but idle speed is rich. I lean the low range idle (stumbles a little at take off) to keep the idle mixture at a manageable richness. 

With CSV fuel line plugged:
- long time to start (understandable), runs less rich at cold high idle. When warm, the high and medium range mixture is still right on. Low range mixture is now horribly lean and idle is lean for the first time! The change is dramatic. I can now correct the idle mixture by adding fuel and turning the air screw to correct the idle speed.

I would have to say that this test proves conclusively that the CSV was leaking excessively (I noted it at one drop/5 seconds). Prior to this test the low range mixture was always much leaner than the idle mixture. This is the first time they are both the same. If I can get the valve repaired correctly so that it doesn't leak, I think I can smooth the twitching engine at idle speed. With the large volume of air/fuel moving in the high and medium engine speed ranges, those fuel drops from the CSV probably made little difference. But at idle speed with a very small amount of air/fuel being moved, those drops were apparently enough to richen the mixture.

Can these valves be rebuilt successfully? I know new ones are astronomical and would like to try rebuilding if there is a good chance of success. What do you think?

One final question: When my engine was rebuilt 12 years /13,000 miles ago by a PO, the injectors were replaced according to the receipt. Do you think they would now benefit from a good cleaning since the car only drove 1000 miles /year?

Thanks for the advice

[J. Huber]

Hi Wallace. Yes the CSV can be taken apart and often repaired good as new. Or at a bit more expense  -- H & R Fuel Injection (Hans) will do it for you. I think there are two problems that arise -- either it gets gummed up and needs to be cleared or the seat inside the valve needs to be lapped. Somewhere here there is an article on how to do it (or was it one of Dorian's?) Hopefully someone else will help.

[ja17]

Hello Wallace,

Sounds like you are making progress. Yes repairing the old one or finding a good used one would be worthwhile.

[wwheeler]

I have become very frustrated with my cold start valve.

I have had it rebuilt by H&R and by Pacific FI and it still leaks. The problem is that sometimes it leaks and sometimes it doesn't. I test it with the pump running and the engine off. I take out the small hex bolt and look for fuel.

It will sometimes leak one drop every 5 seconds and sometimes not at all. The leakage is not linked to engine temperature as it can leak hot or cold. I have also tested the solenoid and it works as it should.

I hate to spend the big bucks for a new CSV, but I don't know what else to do. Anything else I can do?

I have already determined that when the CSV leaks, it effects my idle quality. Before buying the new one, I will drive around with the CSV feed line plugged and see what happens.

Any thoughts appreciated!

[hands_aus]

I was wondering if there are small particles of some sort stopping the valve from sealing properly.
In my case there also was fuel leaking out the side of the solenoid.
When I removed the solenoid I looked into the opening and there were broken seal particles in the valve.
I cleaned it with an artists brush.
Replaced the solenoid seal and everything was back to normal.

[wwheeler]

Thanks for the reply Bob. I will take the CSV off and check for debris. That could be the cause of the erratic leaking.

After driving around with the CSV feed line plugged, I have determined that I do have to adjust the thumbwheel mixture on the IP depending on if the CSV is connected or not. If connected I have to lean, if disconnected I have to richen. However, my idle quality is still a problem either way. At idle it is too rich and at 1200 RPM and above, it is just perfect. All of the tuning I have done has made improvements, but that basic problem still persists. I can lean the mixture for a good idle and mixture, but then the car hesitates and misfires when starting from a stop in drive. The plugs are somewhat sooty and the tail pipe is definitely sooty.

I am wondering if there is something in the pump that may need adjusting? A PO had Pacific FI rebuild the pump 4 years and 5K miles ago. Doesn't seem likely but this problem has been around ever since I have had the car this last year. Maybe it was never corrected? I am considering sending the pump and injectors to confirm that this is not the culprit.

Does anybody have any thoughts on Injection pump?

[hands_aus]

With the CSV disconnected on a HOT engine, that is the equivalent of having a CSV that is working correctly.
My opinion is that you should be able to set up the air/fuel mixture for best CO specs at IDLE (800 RPM +/-).
Figures are given for 1500, 3000 RPM but the injection pumps lean out as the engine speed increases and CO values change at those speeds.
I am sure you know the JoeA air/fuel test. It is very accurate and after a while you will learn what the sound of the engine will be at correct idle speed.

It is very important to have everything on spec eg., timing, linkages etc before you will achieve correct engine running.

Have you oiled the felt wick in the distributor?
Made sure the rotor moves freely.

Clean or replace the plugs with correct heat range plugs.

Before taking the Inj pump off you must try every other combination first. The last thing you want to do is have it rebuilt and have the same problem.