Rough Idle, No Start, CEL, O2 Sensor? - PeachParts Mercedes-Benz Forum

sn0bored · #1 10-26-2009, 11:50 AM

I have a 91 300te 4matic. 205,000 miles. A little bit of rust, otherwise pretty sound.

An issue developed recently. It started as just a rough idle, that sounded like it wanted to die. It then started to die when I came off the throttle. It would usually start up again. After sometime it would be really hard to start, sometimes wait 5 min and it started right up and ran great. It then developed a check engine light. That would come on and then go away while driving. It would continue to drive quite well most of the time. I built a home made code reader I found on this site. I used it in the 16 pin code reader near the battery. Using Pin 3 it gave me a 17 blink code. Which told me faulty or grounded O2 sensor. So I think this is what is causing the CEL. I am not sure if I should just change it out or maybe change something with my fuel/air mixture? I am also wondering if this will fix my other issue. Does anyone know if the O2 sensor can cause a very rough idle and make it hard to start sometimes or did this come from something else going on in my engine. I have heard OVP Relay as well. I also checked vaccum lines and they all looked fine. I posted on another site and that seems to be the canned answer for this type of problem. This forum seems to be a lot more capable from reading many threads. Thanks for the help in advance.

mercafreaket · #2 10-26-2009, 04:18 PM

Check the OVP the first thing you do. Sounds like that. Disassemble it and resolder the solderings, use some electronic cleaner on it as well. That may help.

The KE-Jet is Running in Open-loop mode during the "warm up" cycle so the Oxy doesn't affect the cold starts.

The OVP affects the Cold start, if it fails, it'll cut the power to all KE-functions, even the cold start valve and so on.
What's more that affect the cold start procedure is the engine thermo sender unit, sitting on the cylinder head, maybe between 4'th and 5'th cylinder, injection side.

sn0bored · #3 10-26-2009, 06:00 PM

Thanks for the response. Do you think that means O2 is bad though?

I have a friend who is a Mechanic and he got me an OVP Relay to try out. He said we could return it if the problem is still there. I put it in and everything seems to be running great right now. But the check engine light comes on now and it is solid. So I ran the tester again. Still getting Fault 17 on Pin 3, but now I am getting Faults 2,3,4,5,6, 12, and 13 on pin 14. I found an old post by someone having the same problems and same fault codes. He said he replaced the O2 sensor and MAS unit and was still getting all those codes. Of course he never told us what his solution was

. He has not posted in 2 years but I tried him anyway. I will let you know if he responds.

The AC is also not working now. I will check fuses though. Could have burned out through all this mess. I thought I would add it incase it is some how connected. Well, let me know if those codes and problems makes sense to anyone else. I have the sheet to check them so I know what it says they mean. Thanks again everyone.

sptt · #4 10-26-2009, 11:24 PM

I changed out my O2 in my 300E and some of the idling issues I had improved as well as the fuel mileage. I changed the OVP and nothing improved despite all of the recommendations and disappearing gremlins reported. Out of everything I have done, the O2 Sensor had the biggest impact on idling and fuel consumption. I have a 91 with 170K. I also used the Ford Mustang '05 or earlier version and spliced the wires into the MB connnections. It was cheaper that way. Spin all of your fuses too or get some new ones. The contacts get corroded. I had a power window that was intermittent until I changed the fuse out.

pawoSD · #5 10-27-2009, 01:07 AM

On my 300E when it was doing that I replaced the OVP, Idle Control Valve, engine temp sensor, Crank Position Sensor, and air intake temp sensor in order to solve the problem. Its been perfect since I did that.

mercafreaket · #6 10-27-2009, 07:00 AM

Quote:

Originally Posted by sn0bored

Thanks for the response. Do you think that means O2 is bad though?

I have a friend who is a Mechanic and he got me an OVP Relay to try out. He said we could return it if the problem is still there. I put it in and everything seems to be running great right now. But the check engine light comes on now and it is solid. So I ran the tester again. Still getting Fault 17 on Pin 3, but now I am getting Faults 2,3,4,5,6, 12, and 13 on pin 14. I found an old post by someone having the same problems and same fault codes. He said he replaced the O2 sensor and MAS unit and was still getting all those codes. Of course he never told us what his solution was

. He has not posted in 2 years but I tried him anyway. I will let you know if he responds.

The AC is also not working now. I will check fuses though. Could have burned out through all this mess. I thought I would add it incase it is some how connected. Well, let me know if those codes and problems makes sense to anyone else. I have the sheet to check them so I know what it says they mean. Thanks again everyone.

Sounds like you've got the wrong OVP relay. There are 3 different OVP:s, 1 weaker with one fuse on top+5 pins and 2 stronger, one with 2 fuses and 7 pins and one with 2 fuses and 9 pins (or was it a different 7 pin-out setup?)., if you put a "weaker" OVP some functions will disappear. There's always possibly to put a stronger OVP, the extra legs just doesn't get used.

Just check so the pin configuration (relay outs etc) is matching, then it should be no problems.

And no, your oxy doesn't have to be bad. Just that a faulty OVP will make the KE go completley mechanical, with no feedback from sensors, oxy or anything else. A sort of limp-home...

sn0bored · #7 10-27-2009, 01:54 PM

Thanks guys. It was the 9 pin relay on my old one and the new one i got. I opened the old one and it was pretty corroded. I think the new one is needed even if it is not the specific problem.

I will change the O2. I can do it myself and it is $95 or so from **********. That is not too bad.

I had a NEW issue now too. I have been driving it with the test lever in 2 wheel drive. While taking it for a test drive with the new OVP. It started leaking Hydraulic Fluid once I hit about 50mph. I know this because I had a plume of white smoke coming out of the car. I pulled over quickly and looked under and it was coming from the 4matic and was a clear oily liquid. I am looking at that today as well. I am not spending much on that, just want the leaking to stop. I never need 4 wheel drive in Hotlanta. Maybe 1 or 2 mornings a year.

We are getting near our cutoff of putting money into this car. It is sad because the engine and transmission are great when I am not having these weird issues.

sn0bored · #8 10-27-2009, 03:24 PM

It was the fuse for the AC. I don't know who came up with these fuses but they are terrible. I seem to have to clean them all the time. I put some WD40 on them this time so I hope that helps.

I was listening to the engine just now and it seems to have a slight sound coming from the pass. side of the engine. May be an exhaust leak, but I am not sure. Doesn't sound like a click like the valves. I know this because I have that sound too before the engine warms up. I read/heard this could be the lifters? Well one thing at a time.

mercafreaket · #9 10-29-2009, 06:46 AM

Do NOT use the WD40 or another rust oil in the fusebox, it may help a short while, but then it's transform to a black "goo" that isolates the fuses from the fuse holders. You should use Electronics cleaner instead. There's 2-26 or 7-78 for that use.

sn0bored · #10 10-29-2009, 11:28 AM

Thanks

I thought I read the WD40 idea in another thread. I will pull them and re clean everything with electrical component cleaner.

sn0bored · #11 10-29-2009, 06:13 PM

Problem is back. It was not the OVP. It worked for 3 days or so no problem. Today I warmed the car up and when I got to the bottom of the driveway it cut out. I then tried to start it and it took a few minutes before it would start again. So back to trying to figure it out.

workerunit · #12 10-29-2009, 06:42 PM

You may have a engine wiring harness issue, look carefully at your harness, do you see any cracking on the insulation of any of the wires??

dhjenkins · #13 10-30-2009, 10:48 AM

Quote:

Originally Posted by sn0bored

Thanks

I thought I read the WD40 idea in another thread. I will pull them and re clean everything with electrical component cleaner.

If found that spraying a little CRC battery protector into the cap and then applying it lightly with a q-tip to be an excellent way to prevent corrosion @ exposed contact points.

Also, make sure that the contacts aren't just cleaned, but are bare copper. Sometimes you can get a little carbon build-up that a chemical cleaner can't remove, so a little manual work is required.

Have you checked the usual suspects? Loose/weak grounds and the like? I've seen more than my fair share of phantom issues caused by a bad ground. What about the idle control or the contacts to the ECM (or whatever MB calls it)?

sn0bored · #14 10-31-2009, 08:21 PM

I just read a thread by someone who had a similar problem and he changed out the injectors and it fixed it. He also bought about 20 other parts first. Does any one have a way to see if the injectors are bad?

I will check grounds and wiring harness again tomorrow. Thanks

lsmalley · #15 10-31-2009, 08:30 PM

You may also wanna check your spark plugs or change them and the wires altogether. I'm no mechanic, but I have a 190E ('90) 245,xxx miles on it and I had a rough idle and I didnt know what it was, so I read a few threads and then changed out the spark plugs and wires which solved the problem. I then had my O2 sensor changed bec the last time I had it replaced was when I had my spark plugs changed around 12/06. Car is running great now.