Karl, by pulling the plug on the EHA I was not indicating that a change in idle speed would indicate this part is bad. The fact that idle speed dropped once you disabled the mixture loop control device of the Bosch KE fuel injection simply indicates the computer is trying to increase your idle speed for some reason. This could be because your mixture is mechanically mis-adjusted, your O2 sensor is reading incorrectly, your mixture is leaned out due to air leaks, or a number of other things. At this point, correctly reading the diagnostic plug is what is needed, and I suggest you find a good tech to do that for you.

Steve

Air leak
 

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Hi Steve,

Wouldn't an air leak after the mass air sensor raise RPM without the ECM knowing about it and trying to compensate? The large air duct which connects the mass air sensor to the throttle body
can be where such a leak exists.

A little trick to find an intake air leak is to use a small propane soldering torch to direct the propane gas close to all suspect hoses, fittings and manifold gaskets... Once the gas reaches the leak, the engine will speed up immediately... Just hold the end of the torch within an inch or so of the areas being tested and see what happens. (NOT LIT OF COURSE):beerchug:

What will happen is increased idle speed, but a lean mixture. The O2 sensor will report this to the ECM, which will presumably enrichen via the EHA. However, much else could be going on here, including a bad O2 sensor, so I think it is time to take some readings from the diagnostic socket.

Steve

I had a high idle issue on my 86 2.3L 190e. It was idling fine until I adjusted the ignition timing to spec, which made it idle around 1100-1200 rpm (the timing was retarded by a significant amount for some reason when I got the car). After adjusting the timing made it idle fast, I corrected the fast idle by simply turning the adjustment screw/knob on the Idle Control Valve. I know there are some vacuum leaks that I haven't had a chance to properly fix, and I think the adjustment on the ICV helped reduce the amount of air enough to drop the idle. If yours has the adjustment screw knob, you can try this--just make sure to keep track of how much you turn the knob so you can return to the starting point if necessary. Turning the knob so the screw "tightens" into the valve will reduce the airflow and help compensate for vacuum leaks until they can be repaired.

I would suggest actually looking for vacuum leaks by removing the air cleaner assembly and inspecting all the rubber hoses. Further inspection might be required to see if the rubber boot on the underside of the airflow meter assembly is torn, or if the Idle Control Valve hoses are brittle and loose/cracking.

I personally don't see how the engine can run with the air meter blocked off as suggested earlier. Unless some air goes through the air flow meter to pull down the plate, all the fuel will shut off any time the plate is at the top of its stroke. There are a lot of possible vacuum leak points on this engine, and I wouldn't trust that airflow block-off test. Each hose and rubber part needs to be checked up close to know for sure.

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Hi Steve,

The ECM would enrich the mixture if a vacuum leak were present. That would allow the car to still have some pulling power instead of backfiring and stalling the way they used to do before
the days of ECMs
I would guess that the 02 sensor was working properly, thereby telling the ECM to enrich the mixture.

Disconnecting the 02 sensor temporarily should lower the rpm and make the car act like an
old one with a carb. (eg. backfire and stall when attempting to rev the engine under load).
Is my thinking wrong?

hi Steve i know you was not indicateing for me to change the parts on the car But i got all the parts cheap so i changed all the main parts.
I do value your input on 190e a great deal.
Please keep it up..
regards karl

hi i can not ajust the icv on my (UK 190e) sealed unit but i will still look for air leaks
regards karl

my 190e went to the garage 2 weeks ago for a new mot and it passed ok
On the mot they check the 02 sensor so this part must be ok ?...

Adjusted the timing
 

Hi Archie,

Just curious... when you adjusted the mechanical timing, was that with the vacuum advance disabled and plugged? Isn't that the only way to get it right?
What was the shop manual recommendation ?

This is what I am saying, and the EHA is the tool the control module uses. That is why a drop in speed after unplugging the EHA is NOT a test of EHA malfunction. As to the O2 sensor working properly, it can malfunction in a proportionate way - giving an incorrect lambda value to the control module. This could cause, e.g., an incorrect idle mixture, even if it turns out there are no air leaks. An incorrect mixture can cause idle speed to rise a small amount, or fall.

Thing is, disconnecting the EHA should not cause the idle speed to drop if the only problem is an un-metered air leak, unless there are more problems. Such could include a bad control module, defective OVP, bad or misadjusted throttle switches/linkages.

Steve

There must be a plot in pollution control
 

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Thanks Steve,

I think I am starting to get the picture better now..

Years ago, (in the mid 70's) we were told that having an air pump push fresh air through the EGR valve under the carb... I agreed that it would really help burn unburned gas as a way to reduce
hydrocarbon emission..
Other pollutants might not be affected in this way...
My theory was that the air pump would simply add more air to the exhaust volume and DILUTE the PPM of all the pollution that was being measured at the tailpipe..

Am I wrong in thinking that IF exhaust fumes were dilluted by 50% with the addition of air, then the tailpipe pollutants would measure about HALF of what they would be without the added air?

Ron

Ron, if by 'air pump' you are referring to an air injection reactor (AIR, 'smog pump'), my '91 2.3 does not have one, and on MB's that do, I believe they are only active during warmup, when the O2 sensor is ignored.

My '83 Chevy m'home has a 4bbl and the smog pump is active even after warm-up - but there is no loop control or O2 sensor.

Steve

todays job was to wire bridge 3 pins on the throttle body which i think is the idle control sensor. the revs went down to 750rpm's but 2'mins later the rev's went back to 1500rpm's. so i think i will need a new sensor for the throttle body...i can see the light at the end of the tunnel......
ps I got this little tip from a mechanic at mercedes...for free.