1991 190e 2.6 - Sudden rough idle, hard start, stalling in gear.
 

Hi everyone,

I have a 1991 190e 2.6, auto, with 124k on the clock. Only known issue is a bad valve guide seal, no appreciable oil consumption, just carbon build up on one plug that I clean during oil changes. Plugs and fuel filter has been changed a couple thousand miles ago.

Here's the issue: Within the span of a few days and about 20-30 miles, the car went from running beautifully, to being not drive-able. It started as a hesitation under acceleration one day to hard starting, running really rough and stalling when put in gear or when the accelerator pedal is briskly pushed in by the end of the next day. Seems to idle high too. After the initial hesitation/trying to stall/nursing the revs up, it seems to build RPM as quickly as it should.

I drained what was in the tank and put in fresh gas. I don't see any obvious vacuum leaks, but I'm far from an expert. Fuses are good. If I unplug the ICV, the rev dip into the 500-600's and it barely runs. I don't know what that means, but I assume it's working? Cleaned it for good measure. No lights of any sort, so I don't suspect the OVP, also, OVP fuse is good.

What else should I trouble shoot? Heavy hesitation/stalling under acceleration suggests fuel issue to me, the Bosh fuel injection system is more complex than anything I've dealt with previously.

I've done a significant amount of searching, but honestly, there isn't much resolution is most threads.

Thanks again for making it through the long read.

It's a common issue and I'he seen countless threads that never end up with resolution. What have you tested so far?

Have you tested output from the fuel pressure regulator?

Honestly I haven't tested much, I really don't know where to start.

I haven't checked the fuel pressure regulator yet, what's the testing procedure? I know the diaphragm in it isn't bad because I haven't had any fuel in the air box.

I don't know about the rough running issue as I still have a rough running issue on my 190E and it can be anything with these cars from what I've read. As for the stalling, it sounds like its fuel related. It could be the MAS relay or like in my case, the EHA. Not sure how to bypass a faulty MAS, but as for the EHA, what I did was unplug it and my car didn't stall for a week + while it was unplugged, but when I plugged it back in it was stalling again. I switched it out a few weeks ago and I have not stalled since. The rough running issue is a diferent story. Hope this helps.

Bosch KE-Jetronic Overview - Mercedes-Benz Forum

Part 4 of 6 is the where 190e diagnostics begins. From what I understand the order of tests is intentional.

blake, when is the last time you replaced the distributor cap, rotor, ignition wires and spark plugs? Recommend pulling the distributor cap and checking the condition of the terminals inside the cap and the rotor end ... clean any deposits off both, and if the deposits are heavy buy new replacement Bosch parts. If the ignition wires are original consider replacing them also. Remove and inspect the spark plugs. Replace if more than 30,000 miles since last replacement ... gap per Owner's Manual specification.

There's also a gotcha with the spark plugs on these cars. They can't be resistor type or they'll fry your ignition coil.

I haven't the cap or rotor yet, it's a priority.

I have copper NGK plugs with maybe 5k on them.

Is there a good way to check the coil?

Thanks everyone for your time.

I'll start going through fuel after ignition, unfortunately I don't have the proper tools to test pressure on a Mercedes, I may be able to borrow them though.

I wish I remembered what was on the car when I got it, but it's had the correct style plugs on it for a while now.

Not true. The additional resistance in the secondary circuit alters the voltage wave form and reduces energy at the spark plug. This can increase misfires, which can be felt as a slight idle roughness, and resistor plugs can also increase HC emissions enough to bust a field emissions test due increased misfires.

Many long time owners have tried resistor plugs - that's what most catalogs now show - at one time or another and gone back to non-resistor, which can be tough to find.

If any ignition coils got "fried" it was probably some other cause than resistor plugs.

Duke

I have read it can fry it, but don't know enough to argue it. Do you happen to know a definitive way to test one of these? I could never seem to find that info. I replaced mine with an aftermarket TPI coil (grumble) and my engine smoothed out a little. It didn't fix the issue I was troubleshooting thou.

OK, I should have some time tomorrow morning to do some more sleuthing on the 190e.

My no cost plans for tomorrow are:

-Inspect cap and rotor
-Pull a plug and see what the spark looks like
-Pull a fuel line and see how much fuel is being delivered.

Any other ideas on things I can do without special tools?

Remove the air cleaner and make sure you the throttle microswitch is clicking when the throttle is released. Look at the throttle body and make sure there is both a vac line going into it and a vac plug above that line. Make sure your IAC, micro switch, eha, and airflow meter are plugged in. Look for anything unplugged really. My Egr vac lines like to unplug themselves..

Update:

Cap and rotor look really bad. Cap has cracks, corrosion, and the center is burned pretty bad. I'm going to pick up a cap and rotor and work from there.

So, if I had to put a number on it, cap and rotor fixed about 60% of the issue. Easy start, no stalling, still running rough.

https://lh5.googleusercontent.com/-v...526_103127.jpg

I pulled the plugs for good measure and found something horrific. Now, I know I had a valve guide seal going bad on cylinder #4 but the oil consumption was negligible. Also, the only noise the car has ever had was a little valve tic, nothing worse than any BMW or Jeep or other I-6 with a flat tappet cam I've owned. If you can't tell in the pic, the ground electrode is 100% compacted against the center electrode.

https://lh5.googleusercontent.com/--...526_105116.jpg

I cleaned up the plug and gap'd it to spec and the car runs great. Yeah, I have no idea either.