Injectors or plug wires causing problem?
 

My 1991 190E 2.6 is running rough at idle and low rpms. Once you get to 1200 RPM or so it smooths out, sometimes it idles smooth as well. It idles very rough at startup and then generally smooths out after 3-4 seconds.

Had 60k service just 4 months ago (problem existed before this) and the plugs were changed as well as all of the other items.

Is there a way to tell if this is wires or injectors? Injector cleaner doesn't help but they could still be injecting without atomizing correctly due to age, etc.

brookspw

Rough Idle?
 

Check this out....
http://www.peachparts.com/shopforum/showthread.php?threadid=15346&perpage=15&pagenumber=1

I appreciate it, but it really doesn't have anything to do with my specific problem. Besides, that thread led to no solution.

Brooks,
I used to have a 1990 2.6 as well and
suffered from rough idling.I did a major tune up and still the problem exist.I gave up and took it to a MB mech.He found that my idle valve is bad.
I taught it was the injectors too,but he said,
if its the injectors,the car will hesitate on
accelaration.BTW.Plug wires are brand new.
Good luck!

Check the overvoltage relay.
It is located behind the black plastic cover behind the battery.
It is silver with a clear cover covering a fuse in the top.
Check the fuse.
You can test by jumping pins 87 and 30 with the relay out and see how it runs.
Look at the bottom of the relay for pin numbers.

I understand how, but what is the exact theory as to "why" the OVP could cause this. I have heard some who got "some" improvement in this area but not a complete fix.

I've heard the OVP blamed for everything from excess tire wear to malnutrition in 3rd world countries :-)

Thanks -- Brookspw

Clauserp1, I DO have hesitation on acceleration at times.

brookspw

What cured my hesitation is the ignition coil.
If its the original,I think you have to check it.

The reason the ovp can cause this is that it supplies the CIS control module with power.With the ECU not powered up,the engine will idle too low and rough because the idle air valve is now dead.It is blamed for a lot rightly so.That is normally the first thing I check on any car with an OVP and a driveability complaint.
What many people dont realize is that most CIS engines will run almost as good (exept at idle)with no control unit at all.

Thank you (got your email, BTW). Car started without OVP. I jumpered (while running) the 30 pin to 87 pin and car immediately idled up and more steady (just "stronger" is how I'd put it). Kind of sounds like the OVP is my problem.

While I had the OVP out, I went ahead and cleaned all the contacts on the OVP and fuse contacts. When I put it back in it ran great, drove it around and all was good. I was thinking, "Well, maybe the contacts were just bad." Drove the car later and was back to the same old tricks.

Will order a new OVP tomorrow.

By the way, the date stamp is 1990 (my car is a 1991) so it must be the original OVP (I've only had it 6 months). It was also the Austrian model, which I've heard is somewhat inferior anyway.

Thanks, brookspw

OVP...
 

and now if you have excess tire wear and hear of malnutrition in a 3rd world country, just change that OVP.:D ;) :p :eek: :)

Where is the OVP on a W126 and how much does one cost? Thanks

The ovp is right near the firewall area on the driver's side of the engine compartment with a red top (or sometimes clear) that flips open to reveal a 10 amp blade type fuse...you may only need to replace the fuse instead of the whole ovp although I did replace mine for the heck of it (but still kept my original that was good) .

It should only run you between $55-$65 bucks and is easy to replace.

Alan

OVP Issues
 

I bought my 89 300E, which now has about 180K, a year and a half ago. When I bought it, it had a slight miss at idle and it ALWAYS took at least two tries to start. I replaced the distributor cap, rotor, spark plugs and wires, air cleaner, etc. to no avail. I have put up with the miss and hard starts since then. After reading this post yesterday, I took out the OVP, checked the fuse (which looked ok), and put it back in. When I started the engine, it choked, girgled, spit and basically ran as rough as it ever had, and oh yeah, the ABS light came on. I removed the OVP again and sure enough, the fuse was blown. I replaced it, reinstalled the OVP and walla, the car is now running like a sewing machine (not bad for 180k miles). BTW, with the OVP out, when I shook it a little, it rattled. I'm guessing this is not a good sign (I ordered another one this morning anyway). Has anybody else experienced a rattling OVP? I totally agree with one guy in another thread who recommended that we be more diligent in posting the results of our work. I have read many threads which have numerous replies that just end with no solution (even if the solution is...I tried it and it didn't work...) At any rate, the solution to my problem was....hard start + rough idle + ABS light = OVP.

Thanks for all who contributed to this thread.

Alan

Injectors or plug wires causing problem? (problem solved!)
 

Well...it wasn't the OVP. Or, shall I say, it wasn't JUST the OVP.

Car does seem to run better overall, and the ABS light is off, but the car still has some rough idle at startup and occasionally at an extended stop/idle.

It accelerates very well otherwise. To be honest, I'm kind of back at the injectors or plug wires.

brookspw:confused: