Intermittent Idle Issue

[timm9]

I have searched for quite some time but was unable to find anything that matches my issue.
1982 380SL with 36,xxx original miles. After several summer seasons of ‘hair pulling’ I was finally able to resolve the huge vacuum leak (Thank you Chuck) with the discovery of the cracks in the Air Guide Chamber, and the replacement of the OVP, all vacuum lines and connectors, Idle Control Module, Oil Temp Sender, O2 Sensor, Temp Sensor, and the ‘brain’, I was finally able to correctly adjust the duty cycle with excellent (last long haul was 22.7 MPG up from 15.8) results. The only component that has not been replaced is the Idle Control Valve, which has been cleaned as per many posts on this site and others.
The issue I’m currently dealing with is a very intermittent idle issue, but not the typical high idle. The car starts instantly but each time the idle will end up in one of three different ‘modes’. One time I start the car the idle is perfect at 550 to 600 with no miss or hunting. The next time it will be low at 500 to 525 and hunting slightly. Start the car again and it will run up to 800 to 900. As noted above, I have removed and cleaned the Idle Control Valve several times and upon reinstallation the car idles fine until you restart. When cleaning the ICV I noticed a round piece of what appears to be similar to black plastic that is the same diameter as the interior of the ICV which is ‘flapping’ loose inside the ICV with only one small portion of the border still attached to the interior of the ICV. During the last cleaning of the ICV, I took a probe and pushed the plastic ‘flap’ back into the ICV ‘flush’ with the interior of the ICV cylinder which resulted in 550 rpms at idle, until the car is restarted.
My question is if I remove the black circular piece from the ICV will I be damaging the ICV? Additionally, is there any diagram that is available to review to see where the black plastic piece should reside? I’m not trying to be ‘cheap’, it’s just that I don’t want to ‘change parts’ without identifying the problem and wasting money that could be put to better use i.e. new shocks, and the A/C that needs attention. Lastly, I did previously post a picture of the ICV with the plastic piece in question at this link http://www.peachparts.com/shopforum/sl-forum/320046-whats-sticking-out-my-ivc.html .
Any suggestions, recommendations, and/or diagnosis would be greatly appreciated.
Tim

[smiffy6four]

Have you connected a vacuum gauge? It's a cheap, and very useful tool. You might consider splashing out a few more dollars for a mighty-vac, which will also test vacuum operated devices.

It's a great old-school way to test all kinds of engine issues.

Here's a great site that give some clear examples of how to interpret the readings:

How to Use and Interpret a Vacuum Gauge

BTW, have you examined the rubber seals around the injectors? I remember working on a 78 450SL that had a poor idle and found those seals to be the culprit.

[timm9]

Smiffy,

Thank you very much for the response.

I do have a mity vac and there are no vaccum leaks at this point. I should have also noted that all injectors were removed, cleaned (although I was told they didn't need it) and the rubber seals were replaced when the injectors were reinstalled. The car has plenty of power and runs quite well as long as its not at idle.

I suspect that the 'intermittent' issue is with the ICV and the loose piece of plastic but did not want to damage it if it could be avoided. In my searches I had noticed several posts where someone was referencing an attempt at rebuilding the ICV. Is that possible?

Thank you again!

Tim

[RadioTek]

There was a thread on The Other Board that covered dis-assembling the ICV and cleaning it.
Auxilliary Air/Slide Valve Deconstructed - Benzworld.org - Mercedes-Benz Discussion Forum


If the link gets eaten, go there and get into the 107 forum, and search for air slide valve deconstructed

Good luck,
Scott

[timm9]

Scott,

Thank you very much for the link!

I'll give it a try and see what happens.

tim

[smiffy6four]

Originally Posted by timm9

Smiffy,

Thank you very much for the response.

I do have a mity vac and there are no vaccum leaks at this point. I should have also noted that all injectors were removed, cleaned (although I was told they didn't need it) and the rubber seals were replaced when the injectors were reinstalled. The car has plenty of power and runs quite well as long as its not at idle.

I suspect that the 'intermittent' issue is with the ICV and the loose piece of plastic but did not want to damage it if it could be avoided. In my searches I had noticed several posts where someone was referencing an attempt at rebuilding the ICV. Is that possible?

Thank you again!

Tim

The vacuum gauge can test for way more than just vacuum leaks; it's useful to help rule out various issues on the way to a good diagnosis.

Diagnosing/troubleshooting As mentioned, a lot of different faults can be found with a vacuum gauge, because the behavior of the needle is different from one fault to another. Here are the seven most common scenarios (engine idling and warm):

1. Steady needle, at 15-22 inHg: Engine in good condition. (An engine with long-duration camshaft will have a lower vacuum and a less steady needle, maybe 10-15 inHg with a few “jerks”. That’s still an engine in good condition)

2. Steady needle, lower than normal: Ignition timing too late or vacuum leak

3. Steady needle like in 1. but occasionally fluctuates at idle: Ignition miss or sticking valve

4. Steady needle like in 1. but drops regularly: Valves need adjustment or burnt valve

5. Floating needle, maybe in the range of 10-20 inHg: Carb out of adjustment or vacuum leakage

6. Shaking needle, becomes worse as rpm increases: Ignition miss, blown head gasket

7. Shaking needle, becomes steady as rpm increases: Worn valve guides



I know you are interested in figuring out how to repair the ICV, but I'm not familiar with that item. I just mentioned the vacuum concept as something useful to help pinpoint engine problems.

[timm9]

Smiffy,

Excellent information!

Thank you very much! I will be printing your reponse and adding it to my manuals.

Tim