W124 M104 EGR Vac Leak?
 

Hi All,

Quick question about the EGR on my E320 W124 M104 for those more knowledgeable.

I have been chasing down a strange idle and did a smoke test for vac leaks. Only smoke I saw was coming from EGR, which from what I saw online can be normal. I did a vac check on the EGR and noticed a very small vac leak. I pulled to 25mmHG and it was at 22mmHG after 15 minutes. Im guessing it will keep dropping in vac but I had to head to work so couldn't confirm.

Is the small vac leak indicative of a bad EGR? Im thinking I mightve ruined the diaphragm when cleaning it out...

Thanks!

Where are you testing EGR for vacuum?

If at the small hose, this will not cause a idle issue.

I am testing directly on the EGR

If it took 15 mins for ANYTHING to leak down 3mmHG, that's a non-issue. Anything big enough to cause idle or running issues is gonna be something big, as in won't even hold vacuum for 1 second.

Be aware that the 90s W124's are known for biodegradable wiring harnesses that crumble and cause all sorts of weird issues.

The only way an EGR will cause an idle problem is if the pintle ( valve ) lets exhaust gasses pass into the intake manifold.

You could pull the vacuum hose off on a properly operating car to disable the EGR and idle quality will be unaffected.

Oh I know all about the eco garbage harness... The main harness has been replaced, currently looking into whether the EGAS module harness also needs replacing...It doesnt feel bad but I need to cut it open and see.

The EGR appears to function fine in that it clearly opens under vacuum and snaps back when vacuum is removed. I am not 100% sure if it is shutting fully etc so I am going to try capping the EGR pipes and removing the unit entirely. Will see if that impacts Idle at all.

The smoke leak from the EGR during smoke test makes me think it might be bad. There was a fair amount of smoke not just a tiny bit.

Where are you injecting smoke and exactly where on the EGR is is coming out?

Please define " strange idle " as details matter.

Also, be aware that EGR went away on the M104 at some point. All had an AIR injection system that looks very much like the EGR. ( both are center of head, exhaust manifold side. )

-Smoke going into the break booster w/ the MAF boot blocked off.

-It is hard to say precisely where its coming out... looks like near the top of the valve where it gets a bit mushroom shaped, if that makes sense. Its smoke so hard to quantify persay.

-Based on part #s and my DM I have an EGR for sure.

It is probably leaking from the pintle shaft. One way to check is to spray carb cleaner on the shaft and see if the idle changes, just be careful not to burst into flames from the hot exhaust.

would that sort of leak render the EGR inoperative?

A leaking diaphragm ( where the small vacuum hoses attaches ) would prevent the EGR from opening / opening fully depending on how large the leak is. However, it is never supposed to be open at idle so it's affect on idle will be zero.

Now, in the 80's GM used a EGR valve that looked at exhaust back pressure ( engine load ) and modulated the valve. This type of valve " probably " bleeds control vacuum to air when controlling EGR flow but it has been years since I've looked at this system. I have no idea if MB used this type of system.

A leaking pintle shaft seal is just like and other intake manifold vacuum leak.

You still have not described what constitutes a " strange idle ". ( Nor have you described the ruckus. . . )

Here is some info on the GM valves I spoke of

http://www.tomco-inc.com/Tech_Tips/ttt26.pdf

http://www.tomco-inc.com/Tech_Tips/ttt27.pdf

Thanks for the info.

And sorry meant to describe the idle earlier, just spaced. Car is idling high (~1400 P/N; 900 D) intermittently with no clear trigger for the idle. Some times it is fine sometimes it is not. Sometimes its fine when I start and for most of a trip, then its acting strange when I pull up to my destination. The cruise control also cuts out during the high idle. Car is running fine though even when idling high.

It could be the ETA, which is out for testing right now. I wanted to rule out vac leaks which is how I got to testing the EGR operation after my smoke test.

Idling that high will be a decent vacuum leak. EGR leaking past will kill the engine at idle, not raise the idle speed due to oxygen dilution in the intake charge.

Not being familiar with the M104, does it have some sort of idle control valve? I know the V8's do and they can stick, or the module that controls them develops broken solder joints and causes exactly the behavior you describe. It mimics the throttle plate being held slightly open.

Please expand on: " The cruise control also cuts out during the high idle. "