Missfire at light throttle
 

G'day

I have a small missfire/(surging probably caused by the miss) at light throttle at most speeds. I feel it especially at motorway speeds of 60mph etc.
Under full or heavy throttle its as smooth as a babies skin.

I have replaced the fuel filter today but that made no diff...I'm a new owner of Mercedes and am comfortable with mechanical repairs.

Any advice?

1989 300E
170,000km
Full service history


Thanx in advance

Maybe a vacuum leak?

I think you've answered your own question!:p

Gilly

HAHAHA Gilly :p

What it turned out to be was the ERA or ERG or whatever you call it. I changed it and WHAMOO the car is a completely different beast!!!
What was actually happening was it was starving for fuel which made it feel like a miss. What it was infact was a surge caused by the starvation. Apparently this Valve thingy makes it run lean if its not working.

Now it goes like a cut cat MEOW!!!:eek:

Cheers

That's great. Must have been the eGR valve-Exhaust Gas Recirculation, sounds plausible.

Gilly

Whoops...maybe I'm calling it the wrong thing.
Its a black plastic covered metal thingy that bolts to the side of the throttle body. It has a plug that plugs onto it. It has fuel passing through it too.


Clear as mud?

EHA -- electrohydraulic actuator, controls fuel mixture via the O2 sensor. Bad one will cause mixture problems, in your case lean running at light throttle.

Peter

hmmm - wonder if this is whats wrong with mine


after a long-ish run at high speed (100mph) then stop at traffic, theres sometimes a slight misfire. it gets wrse if i try to hold the revs at 2000 rpm (neutral) - once driving, it seems fine - i get 20 - 21 mpg (UK) (24 / 25mpg US) on 97 RON (88 - 90 MON)

oce got 29mpg (US) on a long [driving-like-an-old-granny] run

An egr valve problem can be diagnosed in two stages.

I. Disconnect and plug the vacuum line to the egr valve. If the problem disappears, then you may have a vacuum problem.

II. I prefer to block off the egr passage with a piece of sheet steel. If the problem disappears, then the egr valve is somehow stuck open -- probably with deposits on the poppet valve. The egr valve would need to be replaced. Or again, there is a problem with the vacauum.

EGR valve where??
 

A little unsure about the location of the EGR valve. On my 126 380se is it the thermostat looking thing with a clear pipe with red stripe that is just on top of the exhaust manifold. I was doing a little inspection and realized that the small pipe connected to it is not connected to anything else. Where does the pipe run to if that is the EGR valve??