Low idle engine speed - PeachParts Mercedes-Benz Forum

#1 05-03-2002, 08:21 PM

1989 260E.
when fully warmed-up, my car idles at 400/500RPM while transmission is engaged. In neutral, idle will creep to 600/700RPM.
This problem has bee persistant for over a year.
I recently had the following done:
valve guides, seals, full tune-up (cap, rotor, wires, spark plugs etc, air/fuel filter, injectors, etc. The problem was present before the job was done and did not improve/worsen after it was done.
The engine will sometime quit (because of low idle speed) but will re-start easily, and idle again at 500RPM.
When cold, the engine takes a lot of cranking before starting but will idle at 900RPM when cold.
Any suggestions?? Thanks
JackD

dpetryk · #2 05-03-2002, 09:11 PM

Sounds like the idle control valve is not working or clogged up and wont allow any or enough air to pass thru it. I would start by removing it and cleaning it out.

#3 05-05-2002, 05:39 PM

Thanks dave.
Where is that idle control valve. What does it looks like.
Thanks again
jackD

J.HIDALGO · #4 05-05-2002, 07:34 PM

under the air cleaner assembly, in front of the fuel distributor. It is a silver metal "T" with an electrical plug at the bottom and two rubber hoses on each side. Check those hoses for cracks and /or holes.

jay123 · #5 05-06-2002, 12:57 AM

Having similar issue with my '90 190E 2.6. But my idle always stays low..hot or cold. Always idles around 500 or so.
Anyway, how does one clean this part? This part has electrical connections to it. How and what to use to clean.

Thanx..

dpetryk · #6 05-06-2002, 09:32 AM

I have made several posts on how I sucessfully brought mine back to life. Search my threads. Details on how to do it are given there.

pshibly · #7 05-06-2002, 10:01 AM

Ok. My mechanic is the prime example of ones who try and rip you off. They wanted around 400 bucks for inspection. I told them my problems, all my symptoms and he told me it would take him around 5 hours to check if and where there is an oil leak, if ABS is bad, and visual check for transmission leak. I told him that the OVP or idle control valve might be causing my rough idling and my ABS light to stay on. He said in no way does the OVP relate to the ABS light being on. What an idiot. He also said that a loss in oil pressure might be causing the misfiring of the cylinders at startup. But all in all he wanted way too much money to do inspection. Why pay him that much money when i can come here and get answers for free. AND i can order parts for way cheaper. Looks like im on my own on this one. If anyone knows of a good shop in the Orlando/Tampa area could ya let me know? Ill keep you posted.

J.HIDALGO · #8 05-06-2002, 02:57 PM

Maybe he just does not know MB's...
As far as a mechanic in your area, I know there are some members here that live n the Tampa/Orlando area that can recommend a GOOD MB mechanic. If everything else fails, you can try our own Steve Brotherton from Gainesville. He is a regular contributor to this site and a super guy (I met him before).
NO, he did not pay me anything for saying this.

Once you find a GOOD MB mechanic, stick with him, you will save money, time and headaches. Good luck!

pshibly · #9 05-06-2002, 03:27 PM

yeah. i agree. while he is specialized in mercedes and bmw this guy definitely goes out of his way to make sure he is charging you for everything. Ill look into Steve, but considering he's in gainesville it might not work out. Too long of a drive especially if i have to leave my car and im college. Thanks.

ItalianBenz · #10 05-06-2002, 06:25 PM

Jack D. Heres a little trick. On the early 300's In side the fusebox
You acutally have to remove the fusebox cover,and the fuse box assembly. Where all the wires. inside the box its self. There a 12 pole harness connector. Its rectangular. pul it apart. Its a solid purple wire. I think its the female end. Pull the plug apart what you want to do is ground that wire i thinks its either pin#10 or 11 wire.Its the purple one. You ground it to the chasis it steps up the idel to addl 50 rpms more you'll feel it smooth out. This is a early upgrade due to alot of the cams
the timing was retarded to get them to pass emmisons.

So try this. I did this on my old 300E when I had it It help
Also the airslide valve could be worn out also. Which is the valve the guys mention to you on the post.

Benzmac · #11 05-06-2002, 09:17 PM

BEWARE !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

If you do the idle mod wrong, you will burn your wiring harness to the ground. The reason is this circuit is hot in the START position.

ItalianBenz · #12 05-07-2002, 03:12 AM

your right donnie. I did one a few weeks back. I guess its not a good Idea these users are not familiar with our systems.

pshibly · #13 05-12-2002, 10:53 PM

Ok. I took out my OVP once again and cleaned the connectors off. there was no visible dirt but i did it just in case. then i put it back in and started on my 600 mile journey. Needless to say not once did the rpm go below 500. Note that the temp outside was well about 90 degrees and i had the air running. I did not expernience any stalling or vibration due to a low idling throughout the trip. On occassion I also had 3 other people in the car and it still did not dip below 500rpm. So i will take it that the OVP connectors just needed to be cleaned. Im hoping this is a permanent fix, although something tells me that wasnt a fix because it didnt cost $$$.

*** Also, the ABS light went out during the whole trip so not only did cleaning them fix idling, but also that irritating notion that the ABS light is on! Looks like we have a temporary fix.