For a while now I have had an intermittent warm rough Idle on my 1987 - 300SE. This occurs once the engine is warm - usually when slowing to a stop( or when stopped ) when the RPM's drop low - Below 500.
I know many elements could be the source of and contribute to such a disposition.
HOWEVER, when I replaced the OVP today , the new one seemed to immediately control the rough Idle. I have a feeling it is doing just that - controlling, rather than eliminating.
I can kind of hear the engine (103) wanting to go to "rough " again and not being permitted too.
Does this narrow a possible cause (for an irritating rough Idle) for anyone ?

Thanks.

PS. Also, could anyone help please wth my post of 9/5/01 Re -Sliding SunRoof -W126....

you may need an air/fuel mix adjustment.
go to a trusted mechanic.

gidpor:

I cured the rough idle/unstable idle hot on my mother's 300E by replacing all the rubber vacuum lines and the rubber hoses from the idle valve to the intake and fuel distributor. All of them were bad, and caused unstable idle mixture problems.

A dirty idle valve will do the same thing -- it gets stuck and won't control the idle properly.

The rubber hoses are standard vacuum line -- take a piece into the auto parts store and get about 3 or 4 ft, then replace all of the short one, between the intake manifold and all the sensors, etc. The main part of the lines are plastic.

The idle valve is under the air cleaner (remove the lower half -- three screws, one in front, one at the rear, one on the side by the fender). The idle valve is held on by two large screws and has a 3/4" or so hose on each side. Single electrical connector, two pins.

The hoses on my idle valve were rock hard and loose on the barbs. The one between the fuel distributor and valve was easy to change, the other one is a bear. The cold start valve plugs into it, and the connection is very difficult to reach from above. Had to use a big screwdriver and a long pair of pliers to force it on, and it has a clamp on it. Much easier from below with the belly pan off.

You can remove the idle control valve and flush the hose connection part with carburater cleaner-- spray some in, shake, it, then dump it out. Repeat until clean. It usually only gets crudded up when the hoses leak.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I had an intermittent rough idle problem on a 91 300 SE. The cure was a replacement of the spark plug wires and rotor. Not all problems are attributable to the OVP!

thanks for the speedy replies. Actually faster and sooner than I can get to attempt these repairs on the car....
I Will have some time off next weekend and try putting this good advice to work then.
will post results later.

peter-
bought and tried replacing those hoses.
i still got those OEM hoses. it was impossible to
replace them. hat's off to you!

peter-
bought and tried replacing those hoses.
i still got those OEM hoses. it was impossible to
replace them. hat's off to you!

Joel:

Yes, it is indeed a pain. The one from the fuel distributor to the idle valve isn't too bad, the other one..... well, lets just say the air was blue.

A pair of welders pliers helps a lot -- they look sort of like needle-nosed pliers but the jaws don't taper. Armor-all or tire-shine (silicone spray) is also very helpfull, just don't use much, O2 sensors don't like it.

It was also necessary to remove the idle valve (it probably needs to be cleaned anyway).

Took two guys to get the other hose on -- one to guide and the other to push to get it on the manifold.

It would be worth it to pay someone to put them on if the old ones are hard and loose on the barbs like mine.

Also did a plugs, cap, rotor, and wires tuneup.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Hi

It has taken me a while to post these (regretfully) temporary results to my Rough Idle post..
Having read all your fine advice - I have gradually tried to address and correct the issue by process of elimination. ...
So far I have replaced fuel pump & Filter, OVP, Plugs , Wires, Rotor & Cap. I have cleaned the
Idle Valve(did not replace the hoses yet...) . Yesterday I finally had the Motor Mounts replaced - the right one was really shot - I am told that one goes first because of heat generated from the exhaust manifold. Driving away I was so hopefull that was it, until I got to the second light...
While I'm not sorry for a second of doing all the above - I have not cured the intermittent Rough Idle yet.
things are smoother, but still when slowing down to a stop , there is a distinct shudder or vibration before things calm down.
No problem with cold or hot start,runs great and doesn't leak too much oil on the garage floor....

Any new thoughts would be appriciated.

thanks
PS - I did have the sliding roof fixed by my local guy. they riveted the back rail into position after I talked them into doing it without ripping the whole interior roof of the car. A couple of hours later after adjusting cleaning and lubricating it works fine.

gidpor:

Is your rough idle a steady shaking or just an occasional rumble? An occasional thump or shake still sounds like the idle valve or hoses -- if the idle valve sticks, then jumps, the idle will drop then surge, then steady -- all happens in less than a second. You may need to replace it, sometimes the motor is shot. Ditto for the hoses -- if they are loose, they will seat by suction, but can shake loose for a spit second once in a while, and you will get mixture fluctuations that can cause a miss. Usually doesn't affect starting since the cold start valve is in the hose at the intake, but causes hot running problems.

If the roughness is constant while sitting, it could be a leaking injector -- you will need to have someone check these. They will sometimes drip at idle rather than spray, and that cylinder will miss.

And check the front flex disk, too -- they go bad about every 60,000 miles and can make vibrations coming to a stop much worse, especially as the transmission downshift.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Peter,

I would have to say it not a constant vibration, nor do I think it is effected by downshifting - it becomes noticable
when the car just about comes to a stop. It wil rumble or shudder briefly and be done with. Almost as if it got over whatever it is..
Earlier on I was advised to go after the fuel mixture...?
maybe I should pull the idle valve out again..

thanks again

gidpor:

Make sure you don't have any vacuum leaks before you start messing about with the mixture, since intermittant vacuum leaks cause the mixture to "wander" -- resetting won't work.

My bet is either a sluggish idle control valve or leaking hoses. If the idle control valve is still sticking, it can cause an occasional stall when abruptly coming to a stop. They can be cleaned, but if cleaning doesn't work, it will need to be replaced. Check to see if the large hose on either side is still pliable. If they are hard, they will work loose and leak intermittantly. This, of course, is the cheap fix.

You could also have problems with the changeover from running to idle engine condition, about which I am ignorant!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I also get a rough engine at idle. At opertating speed the engine is smooth. Would anyone consider this to be an injector problem. Our Mechanic says that Cyl #2 doesnt fire. But at operating speed, and 4 cyl. most cars won't even perform. Any ideas?

I am having a constant idle problem. hard to start nearly dies when put into gear, throttle has gotten stuck a few times until smash and release of the accelerator, very poor brakes(may need bled) is it possible I may have some of the same repairs or am I in a new ballfield, I started looking at the car and seen a sensor that has an arm with a wheel that rolls along the throttle bracket and was wondering what it was and if it may be causing my problem