[Heikkif]

RPM fluctuation and duty cycle would be in sync if if the problem was caused by EHA. Also low oscillation amplitude suggest EHA is responding nicely. Anyhow if it was EHA related disconnecting it should stop fluctuation if it was caused by EHA. Those are my opinions. Others may have different ones.
Do you hear RPM fluctuating or does oil pressure gauge show variation in idle RPM? Maybe idle air valve is sticky. Disconnecting idle air valve cable makes idle high. When I had high idle problem I tested idle air valve with adjustable power source. The one I have has adjustment for current. That way one can run idle circuit in open loop.

 

[John350]

disconnect signal to IACV look for stable RPM ....if not stable maybe send my IACU back to co that refurbished it for further test/correction?

I don't think the Idle control valve will cause the fluctuation, in fact, it should help smooth it out. If it otherwise works (compensate for AC on, trans in drive, etc) then something else (like valve guides or vacuum leak) is the root cause.

 

[Steve86560sl]

Responses to Heikkif and John,

John first:
I don't think valve guides the issue (I'm original owner, car only has 32,000 miles and no sign of any blow back into valve covers ect) or vacuum leak (smoke test OK, only very minor vacuum leak at throttle body shaft seal and duty cycle great at 48-50%).
IACV is fine (really clean and operates fine when bench tested with DC power supply closing linearly and fully closed at 1A, also RPMs seem controlled stepping down from little over 1,000 RPM @ cold start to factory spec when warm and properly operating when A/C on and drops correctly in D.
See below to Heikkif for what I think might be the issue and what I will test for your comments as well as his:

Heikkif, See "you wrote in blue, my responses in black below:
You wrote:
1)RPM fluctuation and duty cycle would be in sync if if the problem was caused by EHA. Also low oscillation amplitude suggest EHA is responding nicely.
As I wrote previously I don't believe the RPM fluctuation correlates to the duty cycle and I agree my low oscillation amplitude suggest EHA is responding nicely.
You wrote:
2)Anyhow if it was EHA related disconnecting it should stop fluctuation if it was caused by EHA.
I will perform this test next time I am with the car and report.
You wrote:
3)Do you hear RPM fluctuating or does oil pressure gauge show variation in idle RPM?
With hood open and listening I can hear (feel is more like it) the fluctuation, no fluctuation on dash tach, dash oil pressure gauge rock solid
You wrote
4)Maybe idle air valve is sticky.IACV is fine (really clean and operates fine when bench tested with DC power supply closing linearly and fully closed at 1A
Disconnecting idle air valve cable makes idle high. Yes I agree;I was thinking with the IACU out of the loop it would eliminate possibility of the IACUs dithering/malfunctioning and possibly causing the flucuation?
When I had high idle problem I tested idle air valve with adjustable power source. The one I have has adjustment for current. That way one can run idle circuit in open loop.
Me too, I did same thing to check operation of the IACV after I cleaned it and mechanically adjusted it to fully close @ 1A..did this on the bench then when installed on the car using the power supply injecting varying current confirming proper operation. I also checked IACU output currents from cold start to warmed up and the IACU was providing proper currents per spec.

BUT I did not check RPMs with the SnapOn MT471 during all above as I didn't have it then.

So.........to close out I think when I am with the car next (won't be for few weeks as I'm out of the country now) I will do the EHA disconnect test and the IACV/IACU test described above.

OK??? Any further thoughts from all?

 

[Steve86560sl]

Just re reading H.D.'s KE primer

Duty Cycle supposed to be:
"In case of engine M116 / M117 of model years ’86 & ‘87 the mean value at idle should be 5-15% higher than the mean value at 2500 rpm."

But in my case I'm getting 48-50 @ idle and 49-50 @ 2500 so I'm not 5-15% higher at idle as I should be.

Any ideas what is causing my reading to be off?

 

[Heikkif]

Did you check pressure difference between lower chamber and system pressures?

 

[Steve86560sl]

Heikkif:
I understand your question regarding pressures but my car is running great under all conditions except the 60-80 RPM swing @ idle.
5 questions:
1) Forgetting pressures for a minute (as other than the 60-80 RPM swing @ idle the car runs GREAT) does the 48-50 DC @ idle and 49-50 DC @ 2500 (not 5-15% higher at idle as it should be) point to the EHA not operating properly or maybe a bad or missing signal issue from the ECU?
2) Why was the 1986/1987 560 SL designed for 5-15% higher DC at idle ?
3) Is it correct to assume the reason one should see a lower DC # @ 2500 is because the EHA should be getting an override signal from the ECU enriching @ higher RPM (lower DC # indicates the EHA is enriching) so the DC # in my case should be less than the 48-50 I see at idle (maybe 44 ?) ?
4) Further confusing me is H.D.s instructions here:
"The mean value at idle should not differ by more than +/_ 10% from the mean value at 2500RPM" but, he goes on to say: "In case of engine M116/M117 of model years '86 and '87 the mean value at idle should be 5-15% higher than the mean value at 2500RPM"
NOTE for other than the 86/87 M116/M117 he only says "differ more than" but, for the 86/87 M116/M117 he says should be 5-15% higher than the mean at idle.
5) So higher only for the 86/87 M116/M117 but, for other years can be lower?.....confusing.

Are there any tests for the EHA?..........
Think I have read EHA coil resistance should be 18-21 ohms....is this correct?.............
Also read somewhere the following current values relate to the EHA:
K on E off: -10 to -20mA
Cranking: -120mA
Idle cold: -5 to -10 mA
Idle warm: +/_5 mA
Under acceleration: > -20mA

Does any of the above sound correct?

Is it possible my EHA is sticking and operating OK @ idle as my lambda variations show 48-50 DC but stay in same 49-50 range at 2500 when it should be differing 5-15% higher?
If the ECU enriching circuit should upping EHA current from +/_5 at warm idle to >-20 under acceleration and it is not this is likely my issue for the DC readings not being what H.D. wants but, would this account for the 60-80 RPM swing @ idle.

Side note:
My cold start is OK but, takes maybe 1.5 seconds of cranking (not instantaneous as others say is norm). As I understand the EHA should see a signal of -120mA during cranking so maybe my EHA is stuck not opening enough during starting??

Does all this maybe lead to a "sticking" EHA...is that one of the ways they wear/fail?

All the above from memory or reading as I am out of country and not with the car.
Sorry for all this but appreciate all the thoughts/suggestions and direction; problem is I am an anal engineer who always wants perfection.

 

[Heikkif]

If duty cycle is not drifting to min or max value EHA is working and is being controlled correctly. If you decide to run warm engine with EHA disconnected observe what happens with duty cycle. Situation with EHA stuck at center position is the same as when it is disconnected.

 

[therling]

I'm currently trying to track down the source of rough idling on my 1987 560SL.

My reading of the duty cycle readings per the shop manual gives me approximately 50% at startup, rising to around 60% at idle when 80C temperature is reached and battery voltage within normal range.

From 07.3.0711 - 121/15 -16 Figures in the left column are %.

It seems to me that if you're at 50% Duty Cycle with the engine warmed up it's an indication of an O2 sensor problem.

Unfortunately, my empirical results-gathering are on hold until elbow surgery recovery but I will be watching this thread closely.

 

[Kingorcus]

I'm currently trying to track down the source of rough idling on my 1987 560SL.

My reading of the duty cycle readings per the shop manual gives me approximately 50% at startup, rising to around 60% at idle when 80C temperature is reached and battery voltage within normal range.

From 07.3.0711 - 121/15 -16 Figures in the left column are %.

View attachment 2806570

It seems to me that if you're at 50% Duty Cycle with the engine warmed up it's an indication of an O2 sensor problem.

Unfortunately, my empirical results-gathering are on hold until elbow surgery recovery but I will be watching this thread closely.

Measure voltage (not %) on pins 2,3 (V3) and pins 2,6 (V6 battery voltage)
and calculate the duty cycle manually using the simple formula
Duty Cycle = [1- (V3/V6)] * 100

I got this advice from H.D's post to eliminate the confusion between different multimeter Duty Cycle calculations. as some calculate on / total and some off/total
If you get a static number that is not changing, lookup the error codes.