Bookmarked. This is excellent. A bit more extensive than the cigar, but excellent. I'm hoping you performed the tests already and started finding out where that leak is.

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1990 190E 3.0L

It would really be helpful if you can post the emission test report. Various values give a good clue as to what the problem(s) may be. Also search for emission research posts started by me, which include easy ways to lower M103 emissions like shorting the R16/1 resistor socket, disablinlg the vacuum advance, and verifing that the installed spark plugs are non-resistor type.

My 190E 2.6 has a five-speed manual and normal idle in Neutral is 700 @ 15". An automatic idling is drive will show lower speed and vacuum, but I don't have any data as to what is correct. These engines have a pretty aggressive camshaft with a fair amount of overlap compared to most of that era, so idle may not be perfectly smooth and may contribute to relatively high HC emisssions.

It's actually likely that the problem(s)may be minor, so don't start tearing everything apart until you research M103 emission test issues as recommended above.

Duke

You might be chasing your tail. Have someone hold 700 rpm while you check for vacuum. Low vacuum is a symptom of low idle, if you have 18 ish inches of vac then your system is ok.

Buy a bottle of redline fuel system cleaner and try that with an Italian tune up.

If you already did the ignition tune up with quality parts, and the vacuum system holds ok, the next thing to change the fuel injectors.

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2

Update for anyone looking for answers in the future. In this particular case, injector holder "O rings" have improved vacuum while driving, I ordered the wrong injector seals, so the old ones are back in at the moment. I suspect that new injector seals will solve the rest of the vacuum issue.

I also replaced what I call the throttle body boot. I doubt that had any real effect, so my advice to those that happen upon this thread, would be to do the injector seals and O rings first, as well as the IAC valve hoses.

I did search for the vacuum leak with ether, while having a multi meter hooked to the O2 sensor, My results did not show any change with ether, but it could have been errors on my part. Also guessing that some of the injectors are leaking down when the engine is shut off, as it sputters a bit upon a cold start. Replacing the injectors when the new injector seals arrive, and I expect the car to start and run well after.

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'83 240D
'85 300D
'86 300SDL
'88 300E

Update: Dirty injectors were the cause of the misfire...

Injector O rings solved a lot of the vacuum leak, but not all of it. I ordered the wrong injector seals so had to pull the injectors twice. Now that the injectors have the correct seals, (rather than the old hard ones) my vacuum leak has increased back to where it was.. drat!

Do the white nylon (mine are yellow now) injector holders shrink or warp in a way that can be a source of vacuum loss?

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'83 240D
'85 300D
'86 300SDL
'88 300E

Please let us know of progress .

Pull off the temperature sensor conecting plug .And try starting the car from cold with out it .

I am not understanding how this will effect engine vacuum, but I pulled both and the engine starts and runs the same. Engine was cold at the time of test, and I am assuming that the plugs only effect fuel enrichment when performing a hot start?

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'83 240D
'85 300D
'86 300SDL
'88 300E

No the temp sensor is in the same circuit as the ovp and cold start system .If temp sensor is faulty it can send wrong message to the ecu, so it weakens the mixture .It can work both ways if stuck , it can send a rich mixture .But if you sure its vacuum , them i would just keep looking till you find it .It can be any place .You have a vacuum holder under front fender next the charcoal filtter ...

Blue have you got a vacuum reading yet .Is it low ,?if so what was the reading.

Thinking about this .As you said the car failed on emissions .Now, did anyone play with the adjuster for mixture settings? .If you say its a vacuum problem ,then you must have some reason to say this . Did the engine ever run right ? thats after you had it. Do you have a vacuum reading.

This was taken from this site we are on.
A lean condition can be traced back to a cracked or broken or torn boot in the system Take off the oil filler cap as the engine is running .If engine is in good shape it will drop engine speed and run rough.. No change is a sure sign of vacuum leak .

Vacuum gage on the dash reads about the middle when idling in drive at a stop light. Idle speed is about 500RPM. Vacuum gage reads about 13" idling in park.

I did a vacuum test with ether, and found NO trace of a vacuum leak, still I tell myself their has to be one somewhere, based upon the dash gage. Also there is an occasional misfire at idle, and I am assuming it is a lean misfire. I replaced the cap-rotor-wires-plugs 200 miles ago. Actually when running with out the OVP relay in while looking for the vacuum leak with ether, the engine ran pretty well. I assume it was running rich, but I did not notice a misfire...?

I will go looking for that vacuum canister on the front fender.

Oh I also looked at the injector duty cycle, and made a small adjustment. That did help the vacuum reading somewhat while driving. I am assuming the previous mechanic made adjustments to correct for other issues. Still need to do more reading about the duty cycle, to understand what is going on. I was attempting to get it in the 44-49% range. I need to focus on aspects of an up and coming trip, so this post is incomplete and a bit rushed.

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'83 240D
'85 300D
'86 300SDL
'88 300E

Not finding any evidence of a vacuum can on ether fender, in the engine room or underneath. What am I overlooking?

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'83 240D
'85 300D
'86 300SDL
'88 300E

I don't think you have a vacuum leak. Check your vacuum at 650 rpm. You should get a reading of 15-18. If you get that reading, no leak.

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2