93' 190E stumbling
 

I purchased this 1993 2.3L car with a fuel starvation problem. 123K miles. The tank has been removed and cleaned, two new fuel pumps (one bad the other was getting more noisy.) Found a bit of fine dust in the bottom of the fuel tank - like body filler dust. Fuel filter replaced twice. The car always starts well but quickly has a stumbling at first take off 1000-1500 RPM or hard low RPM acceleration. A quick rev in neutral also acts like a slight miss at first throttle movement. Ignition has new plugs, rotor, and distributor cap. Found a couple of small vacuum leaks so now the idle is steady except for the more occasional miss at idle. The performance at 2000 - 4500 RPM is very good. Drives pretty good overall except for initial throttle movement (stumble). Gets reasonable mileage. I’m on my second tank with Techtron fuel cleaner. I cracked open each injector fuel line to isolate a single injector but each opened line caused the same effect. Could the injectors (one or more) be spraying poorly at low RPM causing the low RPM stumble? I was told it might take another tank or so of fuel to run the system clean of all contamination in the injectors. I only have a couple more weeks to get my smog inspection so I would like to clear this up soon. Any ideas for this vintage CIS Mercedes? Thanks

Well I just found the EGR valve not holding vacuum when tested with a vacuum pump. Maybe this is it?

Blocked the EGR vacuum - no real improvement. Checked mechanical part of EGR valve for leaks and found it to seal properly, so no vacuum leak there. Has anyone else had this hesitation/stumbling problem???

Lack of enrichment under acceleration could be an indication of limp-home mode. Disconnect the electrical connector to the EHA to see if drivability changes. If it doesn't, you likely have a problem such a bad OVP relay or bad sensor.

Steve

The OVP relay was just replaced just as I bought the car last month by the previous owner. I will check the EHA after I replace the ordered EGR valve. Since I already have it off the car. I did find a couple of rubber vacuum lines off the idle speed solenoid that were hard and not fitting tightly. Also the U shaped one below the solenoid connecting to the bottom of the intake manifold could be moved too.

Ok I guess I don't know what the EHA is? My mistake.

Your problem sounds a little similar to something my 190E 2.0 has started doing just recently. Mine's not quite as bad as yours - the problem goes away once the engine is warm, but sometimes when cold it's bad enough that the engine will stall.

As sbourg says, it seems like a lack of enrichment under acceleration (I'm guessing even more enrichment is needed when engine is cold - hence why it's a bigger problem for me when cold? :D). I have also noticed some knocking/pinking under load when the engine is hot - also a symptom of lack of enrichment??


The EHA I believe is a little - usually black - device attached to the side of the fuel distributor, if that's what it's called. I'm not good with part names. It should have a 2 pin plug going to it. It's kind of the engine electrical component that's attached furthest to the back driver's side (in the US) corner of the complete engine. If unplugged the car should be crap at starting and die/stumble when you push the accelerator, more so when cold. This is certainly the case with my 16v when I unplugged the EHA.

You can measure current through the EHA to see what it's doing but it gets a bit involved for me at that point!