86 300E idle up and down, running rich - Mercedes-Benz Forum

 
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post #1 of 6 (permalink) Old 07-31-2010, 11:45 PM Thread Starter
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Vehicle: 1986 Mercedes Benz 300E
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86 300E idle up and down, running rich

Hi everyone! I'm new to the site, however it's helped me so much so far, i can't begin to say thanks! But with all the posts I've read, I thought I might through out there my issue, and see where it takes me...Where do I start...

Running rich, idles up and down, (suges kinda), lights, dome, headlights, gage lights etc, "flicker" or serge with idle increase or decrease...almost like they are getting feed back from something. ABS light comes on after you start driving.

Now, things I've noticed and done...Car starts up great, runs "COLD" great, but once it reaches normal operating temp, it's running RICH, the alternator was reaplaced and I got a used OVP relay that was suppposed to be good, but not sure if it is, so another one is on the way. I've looked for and repaird any loose or broken vacuum lines. I do smell gas in the fuel distributer, and have heard the EHA valve could cause these issues, but what about the flickering lights? And why would the voltage being put out when cold, around 14v, but then when warm, it struggles to be above 13v. I'm very confused as to which direction to take on fixing her up, if anyone could help I'd be greatful! I'm just stumped. Car has a lot of miles and all, but runs to good to leave alone. I have always wanted a car like this, and so glad I got one, just wish I could drive it. OH, and one more thing, the cruise control surges to, but i read somewhere that is caused by a bad cc amp. No biggie, but just throwing it all out there. lol. Hope to hear back from someone soon!
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post #2 of 6 (permalink) Old 08-01-2010, 12:39 AM
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Originally Posted by nyculc View Post
Hi everyone! I'm new to the site, however it's helped me so much so far, i can't begin to say thanks! But with all the posts I've read, I thought I might through out there my issue, and see where it takes me...Where do I start...

Running rich, idles up and down, (suges kinda), lights, dome, headlights, gage lights etc, "flicker" or serge with idle increase or decrease...almost like they are getting feed back from something. ABS light comes on after you start driving.

Now, things I've noticed and done...Car starts up great, runs "COLD" great, but once it reaches normal operating temp, it's running RICH, the alternator was reaplaced and I got a used OVP relay that was suppposed to be good, but not sure if it is, so another one is on the way. I've looked for and repaird any loose or broken vacuum lines. I do smell gas in the fuel distributer, and have heard the EHA valve could cause these issues, but what about the flickering lights? And why would the voltage being put out when cold, around 14v, but then when warm, it struggles to be above 13v. I'm very confused as to which direction to take on fixing her up, if anyone could help I'd be greatful! I'm just stumped. Car has a lot of miles and all, but runs to good to leave alone. I have always wanted a car like this, and so glad I got one, just wish I could drive it. OH, and one more thing, the cruise control surges to, but i read somewhere that is caused by a bad cc amp. No biggie, but just throwing it all out there. lol. Hope to hear back from someone soon!
Well, im certainly no mechanic. I have worked on alot of my own vehicles though (mostly american :/). But I would want to say that the reasons your lights are flickering and your voltage is dropping is due to the engine not running at a normal idle rpm. At idle, with all the lights and AC on my mercedes operates at about 13.5-13.7. And I notice that with my radio OFF my voltage will go up another tenth. Even if the radio is on but not playing any sound, it still takes away a tenth of a volt.

But since your saying that its idling "rough" it sounds like, id say its more of an engine problem than an alternator problem. Alternators only put out certain amount of power at certain rpms. So as your car is going from say 500rpm to maybe 1200rpm during idle, you might notice your voltage go up and down. Its normal for the alternator to do that, but not normal for your engine to be idling like that.

Thats really all I can help with, if its any help at all. Id say maybe some kind of missfire? Did you check all the spark plugs to make sure they are all firing and are in good shape?

Btw, i forgot to mention, to test your spark plugs to make sure they are firing. There is a few ways to do this, you can either buy a tool (at least believe there is a tool) or you can manually do it by taking out the spark plugs one at a time with the car running and get the spark pluge NEAR the engine block, dont touch it. But if your spark plug is working, then youll see a thin blue spark go from the plug to the engine block. Well, dont take out the spark plugs WHILE the car is running obviously, youll have to restart the car before and after removing and replacing each spark plug.

Last edited by C280Cambria; 08-01-2010 at 12:45 AM.
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post #3 of 6 (permalink) Old 08-01-2010, 01:29 AM Thread Starter
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THanks for the reply. It's hard to put into words how the car's idle is. There is no missing, or roughness. it's just as though your "goosing" the car, from lets say 500rpm's to 1000rpm's. But as far as missing or roughness, there is none, she purrs. lol but the lights dimming down, when the idle goes down, makes sense, it's the weird pulsing/flickering action that doesn't make sense. as the rpm's increase, the pulsing increases. it's like the cars electrical system is surging. I don't know how else to explain it. But i do appreciate the input, and I agree, there is something else wrong with the engine. I'm thinking more and more it's the EHA valve, or a bad OVP relay.
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post #4 of 6 (permalink) Old 08-01-2010, 02:17 AM
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Originally Posted by nyculc View Post
THanks for the reply. It's hard to put into words how the car's idle is. There is no missing, or roughness. it's just as though your "goosing" the car, from lets say 500rpm's to 1000rpm's. But as far as missing or roughness, there is none, she purrs. lol but the lights dimming down, when the idle goes down, makes sense, it's the weird pulsing/flickering action that doesn't make sense. as the rpm's increase, the pulsing increases. it's like the cars electrical system is surging. I don't know how else to explain it. But i do appreciate the input, and I agree, there is something else wrong with the engine. I'm thinking more and more it's the EHA valve, or a bad OVP relay.
So are you saying the car is like, revving itself up and down when its idle? I did some research on OVP relays, as I wasnt sure what that was. And from things I read, that sounds like it would be the problem. Just comparing what youv said and what i read about other people having the similar problem.

I found this for you to read if youd like:

OVP Relay / ABS dash light - PeachParts Mercedes ShopForum

So maybe try tapping on the relay like that guy did? I dont mean to "advertise" another forum by any means, just trying to help.

Last edited by C280Cambria; 08-01-2010 at 02:20 AM.
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post #5 of 6 (permalink) Old 08-01-2010, 09:35 AM Thread Starter
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I'll give it a try, it can't hurt anything lol. It's just weird how all this stuff starts acting crazy after the car is at normal operating temp. OH, and to answer your qeustiong, yes, it's like your reving up the engine just a bit while at idle, only when warm though, when it's cold, the engine runs great, starts out at about 1200 rpms and then with in about 5 min or so it idles it self down to just above 500rpms, once you drive it let's say, just around the block, come back, put it in park, the abs light is on, the idle is up and down, and the lights are flickering. I've got an engine coolant temp switch that i'm going to install today, but i'm not sure that's going to do anything at all.
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post #6 of 6 (permalink) Old 08-01-2010, 04:15 PM Thread Starter
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Ok, so today was spent working with my 300E and I have good news and bad news.

Good news, Idle prob fixed with new OVP! YAY!!!!!

Bad news, still running rich, due to leaking EHA...Bummer, but atleast I have a head start on knowing what to do in this situation...replace it. ha, ABS speed sensor's on front wheels were HORIBLE, they are now clean. And still have prob, took rear wheel off, only to find, there were no pads...:-O, well, that would explain the prob with the ABS light, so new calipers rotors, and pads are next on the list after the EHA, thank goodness I don't have to rely on this car every day. But if it werent for this site, I wouldn't be able to have learned what tiny bit I know now. HOpefully the EHA valve will fix the leaking fuel into the fuel distributer, and then once the caliper, rotor's/bads are all replaced, I....I think the car might be drivable. I'll keep everyone posted on the news.
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