I love this site. I have learned more in 1 week of reading here than I could have learned in a month of Sundays elsewhere.

I have a 1990 300E with a 103-983-12-206201 engine. We have had the car since it was a baby and it is a part of the family. We have taken exceptional care of it. The following is a list of what I have done with OEM parts since the first of the year.
*Removed/inspected/cleaned intake
*cleaned clogged EGR (exhaust gas recirculation) tube
*Replaced all injectors/insulators/o-rings
*Replaced all filters (except power steering)
*Replaced all brittle vacuum lines
*Replaced dist. cap/rotor/plugs(not platinum)/plug wires
*Flushed coolant replaced water pump/overflow tank/rad.cap
*Replaced drag link/tie rod ends/ brakes/shocks
*Installed Euro-Headlights with leveling system (with your help)
*New tires/4wheel alignment
*Rebuilt Starter (just because) same with alternator/regulator
*Installed block heater (what a waste of time- burnt up first time I plugged it in.)
*Changed all fluids/filters (transmission/rear end ect.)
*Replaced reference sensor (old one had a crack but worked)

Now I have the roughest idle known to man. Cold Start is fine but once it warms up it will jar your teeth out at a redlight. Although my dentist is smiling, I am not. I removed the OVP relay and resoldered every joint on it.

My Question;
Is there a way to check the function of the idle valve off of the vehicle? Being the Dennis the Mennis that I am you know that I have already tried. I may have fried it. I applied 12vdc and it opened. When I removed the 12vdc it closed but not all the way. Was not all the way closed before I applied voltage though. When I had the intake off I inspected the bottom of the fuel/air dist. for cracks. (none) I have since inspected for a vacuum leak. Can't find one.

I am getting ready to replace the timing chain, tensioner, oil chain. I thought about going ahead and doing a head job but really do not see the need. No smoke, No fluid loss- coolant or oil. By the way..This car just turned over 150,000 yesterday. The motor is as clean as it was the day I got it---maybe cleaner.

Can you help..I have made a genuine effort to find my answer using your search option. I have learned a lot but nothing that I feel would help.

P.S. Fuel has been flushed and treated- -twice. I am also going to replace the Oxygen sensor (never been changed). I found a great article about how to set the stiocyometric (not sure of spelling) ratio. Lambda point. Using a John Fluke rms87 multimeter I used the #2 and #3 pins on the x11 connector. Setting the average battery voltage at 50% +/- 10% proved futile. The reading at 2500 rpm would stabalize and them move up 1volt/sec to battery voltage, hold for two seconds and then decend 1volt/second to zero. I hate to replace the Oxygen sensor until I find out what is causing the rough idle...Might mess up the pre-cat or the catalytic convertor.

Please forgive my spelling, run-on-sentences and sentence structure. Us Boys from Tennessee just started wearing shoes last year.....you can't expect too much too soo.

Thanks in advance
Michael Granger

Michael, have you done the tried and true method of testing for a vacuum leak by spraying some starting fluid around under the hood with the engine running? The engine will surge when it sucks the fluid through the vacuum leak and lead you to it. Also, go ahead and replace the O2 sensor. If that is not the solution then reinstall the old one and keep the new one in reserve. Avoid any major repairs. It's usually something simple and inexpensive that causes such a problem.

I have stuggled with roughly the exact same problem. My idle is fine cold but feels like it is skipping once warm (very rough to the point of almost dying). I suspect head gasket leak/seep as my coolant is pressurised overnight and understand that head gasket replacement is basically a maintenance item on these cars at 150-175K.

If you find a cure please let us know as I would love a simple fix for the problem as I evaluate options on the head gasket issue.

P.S. Curious if your coolant stays under pressure overnight.

__________________
2008 GL320CDI 6K
1970 280SL 112K
1982 240D 210K (Sold)
1973 220D 220K (Sold)
1967 200D 160K (Sold)
1992 400E 139K (Sold)
1988 300E 148K (Sold)
1987 300D 257K (Sold)
1991 300E 108K (Sold)
1987 300E 131K (Sold)
1978 300D TMU (Sold)
1980 300D TMU (Sold)
MBCA Member

The Idle Control Valve does just what you are talking about. It did in mine.
Don't know about whether you have fried it or not , but with the valve off the car - cleaning it with carburator fluid helps( shaking and then dumping the fluid), then applying some WD40 - a trick I learned here on the forum and works great.

I imagine you could do The DW40 with the valve installed - just remove the hoses and squirt some in....

Hope this helps

PS. I am real curious - was the shoes thing diffcult to get used to ?

I am about to replace my fuel pressure regulator for a rough idle problem. I've read here and elsewhere that this part is a "frequent failer" and can produce rough idle. Not too expensive. Try searching on it and see what you think.

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Steve
'93 400E

hello, I also have this problem, and can't solve out, I have try to replace the OVP relay, but doesn't help anything at all....

to solve out the problem, the last method I am thinking of, is I will send it to the main dealer in monday, and let them have a play...

if I find out anything, I will make reply asap...

For those of you who have a surging idle (once fully warmed, fine when cold) check your fuel accumulators. I have seen this many times. It is fine when cold since cold start injector is supplying extra fuel, once it stops the idle starts to surge.

Vin

Novice q
Where is this idle control valve in a 300E,I am thinking of giving it a squirt too of WD40 as part of routine maintenance.
Thanks

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Tom 2010 C250 4-matic Sport (Canada)

On the 103 Engine, it is under the air filter in front of the fuel distributor . Has a rubber sleeve holding it in place , a hose on either side plus an electrical connection in front.
This should lead you right to it.
I still recommend spending a few minutes taking the valve off and cleaning it.

I encourage everyone to post their findings and results to this or any subject. It seems like in researching this and other issues, posters often post a problem and ask for advice and get feed back for possible solution and then the dialogue ends. I usually assume that their problem was fixed, but it sure would help others (especially those using search function in the future looking back) to know if suggestions worked, if some other solution was found (by mechanic or otherwise) or if problem still exists (good information in itself if suggestions tried and failed and also so that possibly others can give additional input).

On idle issue, many responses have suggested a fix but there is often no indication as to ultimate solution or whether suggestions were attempted.

This is in no way meant to be critical but is meant solely as something to make this board that much better. I personally thing it is terrific and anything that helps make it better should be shared/discussed. This forum and those in it have given me the both the courage, support and knowledge to attempt many things that I otherwise would not have (along with excellent parts support from Phil at partshop/fastlane).

Another way to think about it, is that any time advice is solicited, you are not just seeking assistance for your particular problem but are also providing assistance to those in the future, who will ultimately be faced with possibly the same set of issues.

Just my thoughts. Perhaps this should be its own post heading, if so please advise.

__________________
2008 GL320CDI 6K
1970 280SL 112K
1982 240D 210K (Sold)
1973 220D 220K (Sold)
1967 200D 160K (Sold)
1992 400E 139K (Sold)
1988 300E 148K (Sold)
1987 300D 257K (Sold)
1991 300E 108K (Sold)
1987 300E 131K (Sold)
1978 300D TMU (Sold)
1980 300D TMU (Sold)
MBCA Member

I couldn't agree more. I promise to to give more than a concise update when I solve this problem. I have located some interesting reading about the Bosch KE-5 jetronic fuel injection system at www.Bosch.com. I plan to use the advise from this thread and other problem solving techniques that I have learned through life (Ford's 8-d), Taguchi, ect. to get to the root of this problem.


Michael W. Granger

Do a simple EGR test.
The egr gets no vac. from the ecu until closed loop [ warm 02 sensor]. So , once it opens , it may leak/stick open. This will show as a large vac leak at idle. The ecu also calls for no egr at idle, but if it has opened and sticks open, rough idle will result.

The test is to pull a vac on the egr valve line with a hand vac pump at idle . [ or steal vac somewhere off engine for test.]
At idle , when you pull the valve open, the engine should run pretty rough. When you release it, you should hear it pop closed and eng idle smooth. If it sticks open, you have found the problem. If, when you give it vac., it does not hold the vac., it is leaking by internaly , also causing same .. If so, replace it.

It is common on vac leaks to not be as pronounced with a cold engine as they are running rich til warm and that helps off-set the added intake of air caused by the leak.

Worth a try.....

Hello Arthur, thanks for information will try this evening when I get home. Any chance you could give additional details on locations/landmarks necessary to test (which hose relative to location of EGR). (I am unfortunately only familiar with EGR location on my 240D)

Also, I have vac pump/tester and wasn't clear what was supposed to happen at cold/warm idles when under vacuum when operating correctly vs. incorrectly.

Thanks for your help.

__________________
2008 GL320CDI 6K
1970 280SL 112K
1982 240D 210K (Sold)
1973 220D 220K (Sold)
1967 200D 160K (Sold)
1992 400E 139K (Sold)
1988 300E 148K (Sold)
1987 300D 257K (Sold)
1991 300E 108K (Sold)
1987 300E 131K (Sold)
1978 300D TMU (Sold)
1980 300D TMU (Sold)
MBCA Member

The egr is located on the exhaust manifold. The small vac line attached to it comes from a switch-over valve under the front plastic cover if front of engine.
The ecu sends an electical sig to the sw/ov which opens the valve to engine vac. This in turn pulls the diaphram on the egr , opening it and allowing some of the exhaust gas to recirculate back to the intake manifold, cutting emissions.
The ecu will not send this sig at idle or wot, or until the engine is warm. . [ there are other paremeters for the ecu sig timing, but this is the basics]
So, if you hand pull about 12" of vac on the egr at idle with a warm engine, you are creating a very lean condition [ vac leak] and the engine will attemp to stall. [ run very rough]. This indicates that the egr is opening. Now, release the hand vac and the egr should snap shut. Engine should smooth out. But sometimes the egr sticks open, thus the diagnoses of "Running rough at idle when engine warms up".
There are 2 other test for this situation that I like to do while I am there. One possible is that the diaphram in the egr itself
may leak by and cause an internal leak. The test for this is to see if the hand vac will hold the egr open for a period.
The other [ athough remote] is that the sw/ov has a little vent on it that lets air back into the vac line when the ecu stops the sig to the valve. What this vent does is it lets the line between the egr and sw/ov lose its vac to the outside air and return the
egr to the closed posistion. [ in other words, it is possible for
the trapped vac in the line to keep lifting pressue on the egr diaphram].
A vac gauge somewhere on the intake side of the engine makes verifying these test a little easier.
So, this may/may not be your problem, but it shoud be checked
as it will cause this type of prob. and is easy enough to do....
As an added PS to this test,:
This is also a good test to do on the infamous egr intake tube
blockage at the intake side of the engine on the 104 engines.
There have been many post about it and this test will help diagnose that problem as the tube fitting at the head is just about impossible to get to..

Anyone can guide me where the OVP Relay Switch is for a1990 300E

Thanks

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Edgar
Warminster, PA