I've been reading through the forum for something similar to my problem, not wanting to ask the same question what has already been discussed thoroughly at some point. But I could not find anything that could definitively rule out either one in my case. Here are the symptoms: 91 300TE, with M103 engine:
Engine would start cold in the morning in one turn usually, but would not be able to hold idle. I would have to feather in the gas a bit to keep it running for a few seconds. Then it'll be in the 600rpm range. If I don't help out with the accelarator pedal after cranking it to keep idle, it would die down and it would then take several cranks before I could restart the engine. It also would not help if I keep foot down on accelarator pedal, I have to lift off it and just keep cranking the engine 'til it starts. Pumping it before cranking it would make for longer cranking before it starts as well. I also notice that it takes longer to start when engine is warm (approx. 4-6seconds). Engine would also exhibit slight hesitation when launching off from a stop, like it may die down, however it does not. I have had several occassion when engine died on me when maneuvering for parking. With steering wheel turned already, it could not manage the car without me being quick enough to save it by pressin on accelarator pedal. In addition, idle is not smooth. RPM needle is not steady level. Also, when on cruise control, the speed would be surging up and down slightly. Not enought to alter the speed by more than 2mph, but enough for driver to notice the sensation that the car would be surging on-off.
I know it could be OVP when it's difficult to start when warm, and from what I read, easy cold start on first crank and then loosing it thereafter could be fuel injectors. I need my fellow MB owners thoughts on this.
I've had all sorts of problems with my car and some sound like yours.
What I would suggest, don't make assumptions. These cars are delicate and could be many things.
The problem could be as simple as the mixture of the gas/air like I had with my car when I experienced the idle, hesitation on acceleration and difficult start.
It could also be your fuel filter that is a little dirty. Another problem might be a vacum leak. I really would take it to a MB shop that has the right tools to diagnose the problem.
A guru Mercedes mechanic once told me that OVP relays go bad and should be changed every 5 years or so, most have not been changed. This relay affects a lot more than most people realize, including fuel delivery. He said he has had luck with vehicles displaying impossible to chase symptoms and after dumping money into them, it is often the OVP relay. Something to think about next time you are online shopping or driving past the Benz parts department.
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::Familie von Mercedes::
'00 German Sheperd ("Hans")
'89 300 TE 117k
'92 400E (killed in action)
'68 280 SE/8 (High School Sweetheart)
'95 E320 (mother's)
'60 190D (dad's new project)
'05 A6 Allroad 2.7t (dad's ride)
'84 190E (sold)
'90 300CE (brother's)
I remember that dreadful feeling that you have. I had the same problem for a long time. I ended up buying a new ovp relay, an idle control valve and a cable for the throttle body. The new ovp relay made a difference and made me realize that the icv wasn't working. That also made my abs problem go away. If you still have the old black and silver relay w/ one fuse, i would suggest you start there.[;)]
Thanks for the comments. I have not had any problems with the ABS light. I'll try looking for vacuum leaks this weekend. What about the OVP? Any way (like a test)we can tell if it's not working?
It's a shame because despite 198,000+ miles, my wagon still rides well (better than E320 wagon I've been on). I just dread the engine dying on me half the time when I'm backing out of a parking lot.
I don't know if this is the same type of relay, but here's a page that you can try. http://mbnz.org/forums/forums/thread-view.asp?tid=1201888&posts=4 or this one http://mbnz.org/forums/forums/thread-view.asp?tid=1177868&posts=4
If you think that it's never been changed, you might as well get a new one. The old black and silver relays gave alot of problems. The new ones are red and have two fuses on them. There aren't all that expensive. I bought mine new off of ebay for 30$.
I just went through the OVP thing....my new one should be delivered today. Like yours, I had very bizarre symptoms that felt like ignition, idle or fuel (control pressure and delivery)intermittently. To complicate the diagnosis, I just did the head in February and swapped the cap and rotor the week before the OVP started dying. I had cold stalling, wierd idle at all temps, warm hesitation....all intermittently and only for a few minutes, not enough time to get under the hood and bang stuff. I pulled the OVP (you guys who take it out without taking the battery out must have small hands. I pulled the first control unit and still had a time pulling the ovp out of those tight connections) and shot a load of carb cleaner into the fuse holes. I then shook the $h!+ out of it and let it dry. When it went back in with a clean fuse, the car stumbled once the first time I fired it up and since has been near perfect. There was some slight oxidation of the old fuse, but some tell tale green funk around one of the posts on the bottom of the relay. The idle was slightly rough but the Mustang O2 sensor ($36) was the cure for that.
My take on the OVP is this.....you can go to a good shop and spend $70 for an hour of a tech's time or spend the $70 on a known issue. By the way, my car had the original OVP (the date code was from 1989) and lasted just longer than yours at 209K.
"The idle was slightly rough but the Mustang O2 sensor ($36) was the cure for that."
I gotta find out more about this. How did you find out that a Mustang O2 sensor would work? I have a 1995 e320 and the prices I am seeing at my local auto parts place for the same is about 3 to 4 times that.
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