W124 260E Rough Idle

[Athienou]

Hi.

Wondering can anyone help.

I have a 1989 260E. M103 Engine (No O2 Sensor)

I have a rough Idle with an occasional stall for the past 2 years that I’m desperately trying to figure out.

The revs on warm idle are at 500 RPM. It has a slight shake. I cannot identify if its an Ignition, Fuel or Vac Problem.

Ignition

Checked individual components and all appear to be working fine. The spark appears to be strong on all cylinders. I changed the plugs (Denso Q16TT) and distributor cap (but not the Rotor). Also replaced OVP.



Fuel

I‘ve changed the Fuel Filter and Fuel Pump Relay. Checked Accumulator. I’ve done several tests in terms of fuel pressure and flow. Fuel flow produces 2 litres of fuel per minute which is a good indication of strong fuel pumps. I did a pressure test on the KE Jetronic /Fuel Distributor. On the lower chamber I get 5 bars and on the upper chamber with the EHA disconnected I’m getting 5.4 Bars.

I ‘ve also replaced all injectors (Bosch x 6) and seals.



Vacuum

I’ve done a Smoke Test and it shows no leaks in the Engine Bay. I carried out a Vacuum Pressure Test from the Intake Manifold. Interestingly it went from 14hg to 15 Hg fluctuating between those points. (Have a Video if anyone’s interested) I believe it should be between 18 to 21 Hg and steady. The Vacuum Dial at that pressure indicates Late Ignition Timing.

I’ve also conducted a Compression Test and that indicated 13.5 Bars of Pressure on all six cylinders.



Other Components Tested

I’ve conducted tests on the following and all appear to be working

• The E.H.A
• The ICV Valve
• Potentiometer
• Temperature Sensor
• Crank Shaft Sensor
• Micro Throttle Switch
• Sensor Plate
• HT Leads ( Measuring Resistance)
• Duty Cycle
• Air Intake Temperature Sensor

I’ve run out of ideas at this stage and desperately want to get to the root of the problem.

Thanks for reading.

 

[DREAMER NO2]

Have you cleaned the idle control valve ? And where is the econo meter pointer pointing to at tick over ? A few other things -check fuses are nice and clean. And if they are made of white metal , bin them for ceramic and copper . Start at battery terminals remove clean and grease, same goes for earth points . Dont play with any fuel or injection items as yet . 80% of problems are electrical .You did mention temperature sensor but not engine temperature sensor,, this is the part the send ecu a message of how the engine is operating if it is cold it will make the fuel rich and if hot it will make the fuel lean. Putting above to one side purchase a tin of WD40 and spray over the engine in places and see if engine speeds up .

 

[Athienou]

Thanks for your reply. I have cleaned out the ICV. Seems to be operating fine. Then in Park the economy gauge is positioned to the left but not fully. When I put it into Drive the gauge will go between the left and the middle. Fusebox appears ok and so are the terminals. Checked the Engine sensor today and all good. In addition I covered the engine with WD40 with no variance in revs. While the Vacuum Gauge goes from 14 to 15 hg I can hear the engine hunting. Have a feeling it may be a Vac issue. I previously did a smoke test but there was no leaks discovered. Is it true when you do smoke test certain valves may be open and smoke may escape through the exhaust ????? I took a video of the vac gauge operating, if you'd like to have a look I could post it. Thanks again for your time

 

[rayhennig]

Denso Q16TT

That appears to have a 5 k Ohm resistor. For your engine (and mine) I should expect 1 or 2 k Ohm in the suppressor cap and zero Ohms in the plug.

You have replaced the cap but not the rotor. Hmmm. These engines demand HT components in 1st class condition. And no cheapo bits! So a rotor is called for.

I'm not saying that your HT system is the cause of your symptoms; only that the HT should be beyond reproach.

Good luck.

RayH

 

[DREAMER NO2]

Athienou As Rayhennig above - the ht side needs to be 100% Also If the econo gauge is reading like you say it is,then i would be searching high, and low, for vacuum leak . Youi do need a good set of the right type of spark plugs. i found these tor your m103 engine . Its in uk so in £ i I did check and it is for your M103 . B884T 20 TT And the type Q16TT are not for your M103 engine more like 4 cyl Citroen

 

[DREAMER NO2]

Good observation Ray

 

[Coli]

Hi,

any progress on this?

I would be with a vacuum leak causing this too. A quick check for vacuum leak would be to take connector from EZL there should be suction on that at idle. Although if leak is slight that might not show it.

Plugs need to be old skool non resistor, I would suggest just to buy from Mercedes if available the cost difference is not a great amount.

Cheers

 

[Athienou]

Hi
I did another smoke test and found some smoke coming from underneath the air meter. Looks like it may be a leak in the air meter rubber booth. Will be back from holidays shortly and I'll disassemble. Fingers crossed, it just may be the issue.
Appreciate your reply.
Cheers

 

[DREAMER NO2]

Athienou It looks that way use this free workshop manual . -- https://w124performance.com/service/Main.html

 

[Athienou]

Hi guys.
Just a quick update with my fluttering idle.
I put up with if for the Winter months but I'm now determined to get it sorted.
I did a Vacuum Test attaching the line to the nipple on the Manifold where the Vac line connects to the EZL. The reading slightly fluctuates between 14 and 15 HG. I can hear the engine revs hunting, as if the Revs are falling and something is kicking in to accommodate the lower Revs. Interestingly, I disconnected the Vac line to the EZL from the manifold and there was no change. The Vac reading remained at 14/15 HG. Could my problem hide in the EZL?. Thanks in advance for any advice.

 

[DREAMER NO2]

I will tell you something for nothing ....The ignition circuit must be running 100% . . .Until this is done dont search other areas Then take a look at the wiring loom in the engine area .Your looking for perished wires in the loom, or any kind of burnt insulation . Check all fuses in fuse box, along with clean and grease the battery posts. Check earth points to the chassis and engine . And why did you keep the old rotor arm, after you replaced so many parts . Parts replaced should be the same part number as the item removed so dont fit a part just because it looks the same This might help http://www.w124performance.com/service/Main.htm

 

[Athienou]

I forgot to mention, I installed a completely new Bosch HT system ( Coil, Rotor Arm, Cap & Plugs). I'll inspect loom, fuse box & battery and report back.
I still have a suspicion about the Ignition Control Module. If I remove the Vac line from the EZL when Idling should the Revs remain the same?

 

[Snake Charmer]

Have you done a compression or leak down test on the engine?

 

[DREAMER NO2]

Going back on your notes .Who sold you those spark plugs ? my check tells me they are not for your engine. Shops and makers say this is the one you need just to sell them. You need none resistor spark plugs - NGK BP6EF or even BP6EFS .. Do check yourself or ask on the forum we will tell you .

 

[DREAMER NO2]

Nio nead for a leak down test with the wrong spark plugs fitted .

 

[DREAMER NO2]

Use the list chart https://www.denso-am.eu/catalog/pv/443 you might find the problem fixed with the right plugs in the engine but not 100% sure but its a start in the right direction .

 

[Athienou]

Apologies but I did change the Spark Plugs to BP6EFS but it didn't make much difference. I also did a compression test and all cylinders came back with equal amount of pressure of 13.5 Bars.
In addition, I did a smoke test and discovered a leak on the rubber booth under air sensor plate housing. I thought I captured my gremlin but unfortunately symtoms did not go away when I installed a new one.
I've exhausted most things at this stage.

 

[DREAMER NO2]

Right ,, Econo gauge , where is the pointer on tick over
See video in next post But it is Impoertant ,, dont screw it right in or right out .A little at a time making sure you know how to return it to the original setting after if it dont work. .They do say not to play with this .But as long as you put the settings back to the start posision you will be ok

 

[Athienou]

When at full op temp, the Econo Gauge it positioned 7/8's to the left on idle.
When I slightly depress the accelerator the needle will move fully to the left.
I also notice the oil pressure eratically flutters between 1.5 and 2. Again when I slight depress the accelerator it immediately goes to 3.
May I just say thanks you for you time and prompt replies.
Cheers

 

[DREAMER NO2]

This is worth watching if you feel the need to try it migh help fix your problem