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BenzMacX 04-01-2008 09:11 PM

190E 16v High Idle, cannot rev over 2500rpm
Hi guys,
Its been a while sense my last posting, but my car has been running... decent.... nothing I couldn't handle (exhaust problems, a few fuel problems, spark plug wires...). But recently I have been running into some nastier problems and I am not really sure where to start looking.

The engine will now idle at a little over 2k rpm, obviously VERY high. The car will then begin to shutter as it looses and gains power over 2.5krpm. As you might imagine, it kind of takes the fun out of the 16v.

I am assuming this is just a very serious vacuum leak, how ever my poking around under the hood has yielded no obvious problems. I am unsure how the vacuum system is arranged, so I really just do not know where to begin with this search.

And before this it was giving me some very lackluster throttle response, at idle if I ever so slightly pressed the gas pedal the economy gauge would go to about half way and the RPM would drop.

Thanks for any help,

Turbo E320 04-01-2008 10:51 PM

sounds like my KTM when the intake manifold got loose, check the intake and TB and make sure they are tight

BenzMacX 04-04-2008 07:17 PM

I didn't check tight the manifold bolts, yet, but I will get there (I couldn't detect air being pulled in from there)... I am going to replace all the vacuum lines in the engine compartment first. I did, however start ripping apart the throttle body... Have not found anything conclusive yet tho... I pulled the Fuel dissy off, and pulled the throttle body off. The butterfly valve is still on the plenum. Everything looks mostly in order/nothing obviously wrong.

I achieved a stunning 180 miles to a tank of gas (about 11mpg)... and the first have of the tank was in somewhat normal operation... :o

I don't know if any of this will solve the problem, but I am familiarizing myself with the CIS system and what I will have to do to install my VEMS EFI this summer.

Pictures to follow shortly.


BenzMacX 04-04-2008 07:33 PM

There are a lot of Pictures, so I put them on my website. If you need higher quality pictures for whatever reason, I can send them to you.


dbenz 04-05-2008 05:11 PM

Check your compression and then check your timing. My guess is that the tensioner is not updated and/or on of the guide rails has come appart. This will retard your timing and may have even allowed your chain to jump a tooth.
The reason I say check your compression is to make sure you don't tear it apart and put it back together just to find out you have a couple of bent valves. I'm guessing they are ok since it's still running, but at least you'll know if there is anything else you would like to do when you have the head off.
Drop me a email if you have any further questions - I had a very simular problem, could not get my 16V to rev above 2500 rpm and it had no power.


Tinker 04-05-2008 05:40 PM

E.H.A. or throttle potentiometer?


BenzMacX 04-05-2008 05:51 PM

I put everything back together today, using silicon sealant to seal any sketchy rubber parts (I am putting a VEMS EFI in it this summer, so spending a lot of money on parts I am going to throw away in two months isn't worth it). I also found that I have the old version of the idle control valve and the old ones had a "by-pass" valve that would allow unfiltered air in if it needed it. This was deemed unnecessary later, so I sealed that off as well. I replaced most of the vacuum lines as well.

What do I have to show for it? Well, the high idle is now gone. It idles just fine now, but I still cannot get it over 2.5k. It is also running ungodly rich. Stepping on the gas peddle results in ALOT of black carbon coming out the back (does not smell or look like oil burn, but like I am running VERY rich).

Any ideas why I am running rich?

dbenz, thanks for the reply, this car actually had a major engine overhaul last summer (6k miles ago). The chain, guides, and tensioner were all replaced and an updated, ratcheting tensioner was used. There is no audible chain slap (I am very familiar with that noise... unfortunately). The head was also redone, valve guides and machined to spec, but we also had custom valve seats for the exhaust side machined and installed. They used a much harder material for the seats to prevent them from packing in the future. Intake side were machined back to stock spec so the valves would sit perfectly.

I may end up checking the valves, but because all the cylinders had the same build up on the spark plugs it would leave me to believe that they are all the same, and I doubt that they are all broken... although it is possible that the machine shop screwed up, I have checked the valves in the past and they did move substantially in the beginning, the last time I checked they had not moved at all (it was work hardening material on the valve seats, so that was expected).

I must ask, what exactly was wrong with your 16v? I really hope it wasn't anything you said... :o


BenzMacX 04-05-2008 06:05 PM

I did test the EHA and it was a perfect 19.5 ohms.

I just did the pot test (key on, voltage between top and middle pins of the pot) and measured a value from 0 to 8 v. 0v when it was closed, 8v when it was fully open.

I think the pot is only supposed to go to 5v? This would be a fairly significant error (over 50%) and would mean the fuel dissy would be pumping as much as it could at about half throttle... Or 8v is normal and I still have no idea what is going on...

Thanks for any help,

BenzMacX 04-05-2008 06:30 PM

So my father and I, who is a mod on this form (Jimsmith or some creative user name like that) have come up with an idea to fool the system for the time being. I did a little calculation and it turns out that if I put at 3.704Kohm resistor in series with the pot we could pull the output down from 8v to 5v. I am capable of making a 3.86kohm resistor which would make my engine run a little lean for the time being, which I am ok with (I rarely run it WOT anyway).

This would be done already, but I just wanted to make sure that the correct reading from the pot is, in fact, 5v.


BenzMacX 04-05-2008 09:11 PM

I am an impatient sob, so I went ahead and did the resister trick...

didn't work.

Any ideas?

*edit* when I say it didn't work, I mean I am getting the correct voltage drop on the potentiometer now, but it didn't fix the problem...

BenzMacX 04-06-2008 06:34 PM

*problem solved*

After doing everything, really, everything (including checking my timing, and solder connections on the ECU and EZL boards) I decided to take a step back, and readdress the problem.

The problem: its running EXTREMELY rich.

so... is there a way of changing the mixture?

The way I always thought these things to work was that the lambda sensor would more or less set the fuel/air mixture. Then I remembered, I have a gray market car, it has a cat and passes emissions, but it does not have lambda! (1985 euro import, euro did not require lambda, so the dumbass who bought it didn't get the emission system, only to be very disappointed when it had to get federalized. I am shocked that it got through without lambda in CALIFORNIA...) So I did a little research, found this thread:

Not having a DMM with a duty cycle, I just went at that little hex adjustment screw (behind the air box, infront of the fuel dissy) and turned it 3/4 turn (thats a HUGE amount for it, should be done in 1/16 increments) and checked out what happened.

Solved the problem.

Took it for a drive and it seemed a little lack luster, so I enriched it a little more and it seems ok. However, the current flowing to my EHA is incorrect, it should be between 15 and 30mA, but mine is at 10mA and adjusting the screw did nothing to effect this. Any ideas?


pentoman 04-11-2008 08:17 AM

This is a surprisingly recent thread, assumed it would be years old!

From your first post I thought it sounded like EHA adjustment would fix it. I've been playing with mine and it can go so bad that the engine won't rev over a certain RPM.

Which way did you turn the EHA? I have heard clockwise is rich and that it's lean! My car had poor response which I'm solving with the EHA adjustment but knowing whether I'm leaning or richening would be a massive help!! Perhaps lean/rich aren't the terms to apply as it's the "control pressure" I believe it adjusts. by the way mate this may be v helpful to explain KE Jet.

By the way it's worth knowing that adjusting the EHA apparently seems to change the whole mixture too, which can then need correcting using the idle (tower) adjustment.

Man I wish I had some explanation of this!

BenzMacX 04-11-2008 01:23 PM

Yeah, I am not really sure how all this damn CIS crap works, thats why I am going to VEMS as soon as I can.

I turned mine clockwise and I was most definitely running rich, so Clockwise leans it out and CCW makes it richer, however I adjusted the tower, not the EHA itself... I am not sure how to do that....

Good luck,

pentoman 04-11-2008 02:32 PM

Oh right ok.
That's weird because I thought the tower adjustment was clockwise richer............

BenzMacX 04-11-2008 04:03 PM

The link in one of my posts up above has a page on mercedes shop where psfred explained it. I would have followed all of his directions but I don't have a multimeter with a duty cycle measurement on it... they are probably pretty cheap and that is the best way to correctly adjust it.

I know that dissy has two pressure chambers, and you control the pressure on one of them. This creates a pressure difference between the two chambers, but how that changes the mixture I am not sure.

I can't wait for a fuel rail and electronically controlled fuel injectors :)

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