Eha was swapped out with a new one not too long ago, however I did try unplugging it and the car stalled out

Ok, so here's a discovery I made. I start the car and the idle goes up to like 2000-2500 rpm, but with the air cleaner off I can deflect the plate a little and the rpms drop. Depending on how much I press the plate down determines how low the rpms go. I can deflect it and hold it to the spot where my idle is stable at about 650-750 rpm. Hopefully this info can help someone to help me figure my problem out.

Ismalley, you need to go back to basics. For the engine to run, it needs air, fuel, and ignition. You have been messing with fuel trying to get a slower idle. Too much or too little fuel will slow the engine down because the fuel mixture is going rich or lean. That is not the way to set idle speed. If the idle speed is to low then fuel or air may be the cause but if the idle is to high, there is too much AIR and the eha is adjusting the fuel to keep the proper mixture. You need to be looking for how the excess air is getting in. Vacuum leaks, IAC problems, throttle plates not adjusted correctly, etc. Remember, the plate you see does not regulate the amount of air, it measures the amount of air.
I am not familiar with the 190s but basic engine operation is a constant.

I hope this helps.

Paul M

Aye, idle on these cannot be adjusted it is electronically controlled via the IACV.

You can introduce vacuum leaks or disrupt the control system and cause an idle change.

A common one is a 1500 RPM idle due to a broken or non-contacting throttle micro-switch.

I would set the lambda tower to 40-50% duty cycle as measured by the X11 port's pin 2/3.

EHA should be set by fuel pressure gauge set. I can't remember the number though.

Once you get those set and you still have an idle problem then I'd suggest trying to find the vacuum leak.

Actually, the air leaks must be eliminated before any adjustments to fuel controls are made, otherwise the feedback of exhaust oxygen content will cause the ECU, via the EHA, to attempt to self correct the mixture. See comments of pmckechnie, above.

91 500sl hesitation out of the hole
 

hi, I have a 1991 500sl with an intermittent problem that seems to happen when outside temp is above 80 degrees? I give it gas and it hesitates for a second then takes off.
any ideas?

aye, backwards I am. :eek: Fix the physical mechanical issues, then adjust the electricals.

So, where are we at with this?

My system does not appear to have any vacuum leaks that I have detected: 18-20 mm Hg at the intake on various test points. I checked all of the test points and all held vacuum. I replaced all the plastic and rubber hoses again for peace of mind including sealing all the injectors again. All check valves are functional. Sprayed 2 cans of carb cleaner around the engine for about 45 mins checking for idle change and got nothing. However I too my car to a long stretch of road in the middle of nowhere and started toying with the fuel-air mixture again. I had to lean the mixture out a good amount in order to get my car where it is now at. So now, my take off/acceleration is superb! Not sluggish at all, very responsive/quick. The downside is this: #1 my IACV is still disconnected because if it gets connected the idle is way up to 2500 rpm. Also, sine the car is leaned out so much I have to give it a little gas to get it going when starting it. I did richen up the mixture again just to be sure and he start up was great. one crank and it fired right up, but then my acceleration suffered greatly, so I leaned it out again and left it like it is. I am still searching for the answers daily, but I need my car to drive safely so that why I am leaving it this way until I can find more info......8-10 seconds to get across a 4 lane intersection from a red light is not ideal,

Thanks for the update.
Please keep us posted.

Regards,
Eric

Have you bench tested the cold start injector? If it were leaking that would enrichen after all the controls. And if it wasn't working properly it would cause hard starts.

Yep, tested that last week along with all injectors, then I resealed everything. I still get an error code 17, o2 sensor shirt to ground or positive, but that existed before problem occurred, plus I just replaced the O2 sensor and I traced the wiring from the o2 sensor, all the way to the ecu. I even removed the thick black sheath to make sure the green and black/white/red wire were visible and I saw no shortage. I then sealed all of that back up.

I'm interested in starting an open source project to bench test these components. (Like the computer). I have experience with the arduino and real time systems written in C code. I write Java code for my job, but program in a multitude of other languages.

liquiddog,

That would be a fun project but not that simple. Testing components is a
snap but building a system to test/diagnose a computer would be a massive
project. The biggest problem would be the fact that every model/engine would be different requiring different hardware and software to do the testing. There
are so many variables that you would need the source code from the computer in the car you are working on. That is why scanners for the new cars are so expensive. The hardware is not that costly, it is the software. I am sure that you know all about that.

I am in no way trying to discourage you, just making comments about the difficulty of the project.

Now, lets get started.

Paul

Your idle is probably high because the potentiometer is not aligned correctly. It has a huge influence on idle speed.