Air in fuel line at pre filter
 

I'm still looking for the cause of my stuttering/hiccuping engine problem - poked around some more and cleaned up the fuel lines a little bit and noticed that sitting with the engine off, there is about an inch of air up in the clear line by the pre filter. Is this normal? I have a set of fuel lines and SOV o-ring on order in case there is a subtle air leak. The lines now look rather old, and that particular fuel line is pretty dark amber, so the air was hard to see. They could all stand to be replaced.

Further questions - it looks like I have to take the whole intake manifold off to get everything. Is that true? If so, is there some sort of gasket underneath it, or does it just mate up to the head? Also - is there a torque spec on the torx bolts? I have had experience over tightening steel bolts into aluminum things...Also - is there a torque spec on the bolts on the SOV housing?

Previous posts mention the cheesy plastic CCV tubes which become embrittled over time - these were replaced last year when I had some work done under there regarding those darn resonator flaps, so if I'm gentle enough they should be OK. While indy mechanic was there, would have been a simple job to replace the old fuel lines, but I guess sometimes there's a judgment call to just fix what's wrong and not go crazy and getting into everything.

Thanks,

I am not sure which vehicle you are speaking of. On My own and others with the same Model it is common to have an Air Bubble in the Plastic Filter.

when you reeve the Engine the shape of the Bubble may change some but what you don't want to see is the Bubble or a string if tiny Bubbles moving on into the Fuel Supply/Lift Pump.

If you are speaking of your latest model Mercedes I have read that the Fuel Pressure Relief/Overflow Valve has some tiny Plastic Part inside that deteriorates.
On the Same later Models the Fuel Supply Pump has Disc Valve that do not hold up as well as the type of Valves on Mine.

New Style fuel Supply lift pump rebuild
OM606 Fuel Pump Rebuild - PeachParts Mercedes ShopForum

From his description it sounds like he's talking about the 210 chassis. The manifold does not have to come off to replace the fuel lines, but the coolant reservoir does. My personal opinion is that you have much better access with the manifold off. Once you've removed the manifold a few times, that becomes about a ten minute job and is well worth it to me. There is a metal gasket needed for the manifold. An excellent description of the job was done several years ago by Lightman - a search should being it up. The air bubble in the fuel line by the prefilter is not something to be concerned about. If you haven't replaced your fuel lines in a very long time, then that is certainly good insurance. Also anytime you disturb the prefilter, you must change that O ring.

You should also make sure you aren't leaking on top of the injector pump from the delivery valves. That area should be bone dry. If there is any wetness there, new O rings are needed. Lots of info on the delivery valves on the forum too.

FOLLOW-UP:

I read up on common causes of the bucking/stuttering problem, including the EGR workaround procedure, but it seemed like such a kludge to me - I took the car in to K&H ******** in Houston. They confirmed the intake flaps are working OK, and the EGR itself is operational. They even tried a refurbed ECU - long story - to no avail. The stuttering remained. Finally the mechanic told me that frankly he could not find the actual reason why the car had the problem, and he could keep digging around but in his opinion he'd just disconnect the EGR and drive with the check engine light, since it doesn't really hurt anything although if it's on all the time you don't know when something else goes wrong.

After all that I did the EGR workaround where the EGR tube is cut and blocked on the exhaust side, and small air filter is put on the EGR "intake" - the EGR itself is still operational - present and accounted for as the '97 ECU demands. Forum member jfulford also recently did this.

I tend to be a skeptic when I repair something - I usually give things a month before I declare a fix a success - but after 250 miles things are OK - no stuttering and mileage seems to be up - will report back after a couple of fill ups.

Thanks to all who responded to my other long-winded posts.