Good evening guys. I am chasing a code 5 (EGR failure) in a '93 300E 2.8L, California car. The car passes emissions but won't pass the test since the CEL is on.

I read and followed all the posts I found on this topic (thanks Arthur and others!) but I still have the problem. I reset the CEL to clear the code but it comes right back. Code 5 is the only code I get. Here is what I've done thus far:

- Check manifold vacuum: Manifold vacuum is 24" Hg at idle, at normal operating temperature, measured at the hose that feeds the SOV going to the EGR.

- I stroked the EGR valve using a hand pump. It opens and closes normally. It closes with a nice audible SNAP when I dump the vacuum suddenly.

- I checked operation of the SOV that sends vacuum to the EGR. There is no vacuum at the SOV outlet port until the revs get to about 4000, then I get 22" Hg. Below 4000 rpm, there is no vacuum so the SOV is not opening. I do not know if this is normal.

- Ran engine at idle at normal temperature and stroked the EGR valve using the hand pump to see if the engine would stumble. Nope. No change in engine idle. Still ran just fine, no loping or rough running. Based on that I assumed the tube was blocked.

- Removed EGR valve body and cleaned it. On the bench, I tested it, blew air through it, soaked the valve internals in B-12. On the bench, the valve begins to open when vacuum gets to 4" Hg and is open fully at 8" Hg. It works fine on the bench, holds vacuum, and isn't sticky. It does bleed off vacuum r-e-a-l s-l-o-w, like it will drop 1" Hg in a minute or so. This might have been my connections though.

- Sprayed a bunch of B-12 into the EGR tube and let it soak for an hour or so while I cleaned and tested the EGR valve on the bench. Then I used two bicycle brake cables hooked to a drill motor and roto-rootered the EGR tube real good for about 5 min. A bunch of black crap came out. The cables went into the tube about two feet and wouldn't go any further.

- Reassembled the system with a new EGR base gasket and torqued the two nuts to 10 N-m ( I couldn't find any torque values for these nuts in the Technical Data Book so I just used a typical torque value for an M6 fastener since that's what these are).

- Ran engine and again stroked the EGR valve using the hand pump. No change in idle, no stumbling due to lean mixture.

So I must have done something wrong. There is no way the tube could still be blocked.

Does the throttle butterfly have to be open when roto-rootering the EGR tube? I did not open it.

Thanks guys ! ! ! !
Pete