Rough Idle after EGR tube cleaned
 

I removed the intake manifold last night from my C280 to gain access to the EGR tube to fix an egr low flow problem, during the process the (crank case?) Breather Hose (Part# 1040943582) cracked in 3 places and was very brittle. I made a makeshift hose from 1/2" hose although the original was 3/4" hose. Now after removing and cleaning the EGR tube and putting everything back together the engine idles rough below 800 RPM, it sometimes drops to about 500rpm then catches it. Anything above 800/1000 RPM its smooth as silk. I'm wondering if the engine needs to re-learn its gas mixture at idle now that it has a completely clean EGR tube, or is it possible if the breather hose being a different diameter in any way can effect vacuum in turn effecting idle? Also, I had the dealership clean the EGR tube about 2 years ago, but when I removed it last night it was caked solid at the end. However 2 years ago I did replace the EGR valve and switch over valve, and although the engine is idling rough it has not thrown any codes to turn on the check engine light. Sorry for the long post, I just wanted to give all the details. If anyone has any suggestions please let me know.

Thank you and have a Happy Thanksgiving!

My guess is that you created a vacuum leak. The EGR valve is not open at idle or rather it is not supposed to be - disconnect the vacuum line to it and verify that it makes no difference. If there is vacuum in the line at idle the EGR will go open and mess with idle. I would place vacuum to the valve and verify that it does mess with idle. The point being to determine whether the valve is closing (they have been known to stick).

There is nothing you should have done that requires any computer resets except maybe clearing old EGR codes. While HFM cars adapt slowly the closed loop O@ sensor control should handle mixture and will correct for vacuum leaks to a point. On a HFM car the adaptation to limits could take a week or more to set a light if a new air leak can't be adapted to.

Make sure the EGR pipe is sealed at the back of the head at the union. I had a tech aquire that leak once on cylinder head removal. The systems almost covered it up. The only symptoms was a varying idle speed.

Definately sounds like a vacuum leak. When pulling the intake (I don't to clean the egr tube) you should replace both breather hoses 104-094-35-82, and 36-82 as well as the intake runner seals, they are not expensive. I had a#5 intake seal drop onto the starter during manifold installation once. Didn't notice it until the idle was goofy. Check carefully under the intake and between the block and starter to make sure one didn't drop. Another sneaky vacuum leak is where the purge line connects to the throttle actuator. Sometimes the line has tension on it and fiddling with things lets it pull loose.:cool:

I've replaced the breather tube and checked all vacuum lines (I can see) and confirmed the EGR valve was not stuck last night. I think the car has adjusted for most of the idle problem however it now surges repeatedly at speeds of 3-5MPH. My friend helped me with removing/replacing the intake manifold as I was removing/replacing the EGR valve and changing oil so I don’t know if the throttle actuator had a vacuum tube going to it(?), does someone have a picture of it on the M104 engine? That would be the only vacuum line I cant see. If the vacuum line was disconnected from the throttle actuator would it stop my cruise control from working?

Thanks guys,
Brad

The line I refer to can be traced from the purge valve. It's the larger black line. The vac leak wouldn't affect cruise though.

why id my idle surging?
 

Often , 'surging' at low/moderate throttle openings is an early symptom of either ETA wiring failure or main wiring harness failure. Check your wires carefully for cracked insulation on the individual wires--slit open the bundles and look carefully. LOTS of wire insulation failures.

Turns out there was a leak where the EGR tube bolts down on the driver side of the engine. We jacked the car up and my friend who helped me take it apart origanally because of the low flow rolled under and said "Well, I see the problem" So I asked, what is it? He said: "I dont want to tell you" (So I thought it was something bad of course) He had only turned in the bolts loosly that hold the EGR tube and never got them tighened down. So with a #10 wrench and about 2 minutes total time the problem was solved, she purrs like a kitten again.

Thanks to everyone for the suggestions, if it werent for this website I would have taken it to the dealer and had it cost $375 again, but knowing there is support like this when I run into a problem really helps.

-Brad