230SL Engine Idle Oscillation 1200.500..1200..500 every 3 to 5 seconds - Fixed!

[mistertj]

Was messing around with the idle adjustment. Did the linkage thing and all seemed ok. The engine was at temperature (warmed up) and idling up around 1200rpm, which I wanted to get lower. I tightened the air/idle adjustment screw to lower the rpm to around 900 but then the oscillation started...rpms would go down to around 500 and then up to around 1200 and down and up...and continue. Opened the air adjustment, the idle increase to around 1100 to 1200 and the oscillation went away. Before I start messing with anything, thought I'd ask if anyone ever had this issue and what was the cause...or if anyone has an idea of what is going on.

p.s. The injector pump is new to the car and runs great otherwise...except that there is some exhaust popping until the engine reaches temperature.

Update - Noticed the other day that even with the engine warmed, air was being sucked in via the WRD. I put a different assembly on and now engine running great!

[mrfatboy]

Have you made sure your CSV is not leaking? I know you were having issues with it last week or so.

The exhaust popping during warm up could indicate that it is running lean at this time.  Maybe try adding an oval shim under the WRD.

That's all I can think of until the pros chime in.

[Pawel66]

I had these oscilations as well. What I noticed:
- when I had idle mixture way too lean, the engine just stalled after warm up
- when I enriched it a little bit - it went into this oscilation
- when it was set even richer - it was just working normally

And to quote mrfatboy: That is all I can think of until the pros chime in.

[mistertj]

Could be that it's running too lean but not sure that adding shims will richen it. Thought that would make it leaner and/or fewer shims would richen it. Maybe I have it backwards?

[mrfatboy]

For controlling the FIP mixture during the warm period only:

Removing oval shims under the WRD leans the FIP

Adding oval shims under the WRD enrichens the FIP

[wwheeler]

Normally, wide oscillations at operating temperature are indicative of being lean. But, if you turned the air screw in that much, that would richen the mixture. Usually you do not use the air screw or the FIP thumb screw by itself to change the idle speed. It must be done in tandem.

1200 RPM is pretty far away from the recommended idle speed. I might also check to see if the WRD is shut off and the CSV is not leaking when the engine is at operating temp.

The popping at cold idle could be lean during warm up as said earlier. You can do the split linkage test to determine if it is or not.

[FresnoBob]

I was also running blind until I bought an air / fuel mixture meter from Innovate Motorsports:

https://www.innovatemotorsports.com/products/lm2.php

Now I know if my engine is running lean or rich during each warm up phase.  I think this is the best way to adjust shims / air flow screw and IP thumbscrew to get smooth cold and warm running. 

[mrfatboy]

I was also running blind until I bought an air / fuel mixture meter from Innovate Motorsports:

https://www.innovatemotorsports.com/products/lm2.php

Now I know if my engine is running lean or rich during each warm up phase.  I think this is the best way to adjust shims / air flow screw and IP thumbscrew to get smooth cold and warm running.

Well worth the money and then some👍

[mistertj]

Where on our Pagoda's does the sensor screw in?  Would rather not be drilling a large hole in the exhaust.

[mrfatboy]

You can stick it in the exhaust pipe.  You will need to also need the bracket. Look.around for best price and make sure these links are latest and greatest.

Innovate Motorsports 3728 Exhaust Clamp Cast-Stainless https://www.amazon.com/dp/B000CO9MF8/ref=cm_sw_r_cp_api_i_2VQWEb61PMXRY

Innovate Motorsports (3837) LM-2 (BASIC) Digital Air/Fuel Ratio Wideband Meter incl. Bosch LSU 4.9 https://www.amazon.com/dp/B001S7W836/ref=cm_sw_r_cp_api_i_-XQWEbVW75FK1

[mistertj]

Question? If you go the Air/Fuel ratio meter route do you still do the vacuum gauge iterations?

[jeffc280sl]

i have the lm2 device.  it is also a good data logger.  i used mine to tune my fip to the BBB on road dyno specs.   here is a pic of the lm2 on the passenger seat.  also showing is my old laptop showing afr, rpm and map.  the device is mobile and performance data can be collected while driving

[mistertj]

That's neat Jeff. What are the "numbers" you try to "tune" to? Where can I loo up what the "numbers" should be for my 230?

[stickandrudderman]

It worries me when I see people recommending making adjustments that might be totally unnecessary. "Hunting" is caused by a lack of fuel.
First thing to do is the split linkage test here:
https://www.youtube.com/watch?v=28uD3JVbQ-I

[jeffc280sl]

i assumed the linkage adjustment had already been performed.   stick is correct.  adjustments to the fip are considered only after exhausting remedies such as linkage adjustments.  99+ percent of members should stay away from thinking about adjusting the white and black screws on the fip.  all that said the LM-2 is a good device to check afr in the shop and on the road

here is the afr spec for 280SL

[mistertj]

Awesome video. Thank you. It's puts the words into motion. My situation is exactly that shown in the video. A slight increase in rpm when opening the throttle body butterfly and then decrease. Doing the injector pump rod and the engine tries to die.

On a side note, after reading some comments regarding the WRD, it moved me to check to see if there was still air sucking through the device when the engine was at temp. Sure enough, there was some suction, so I removed the whole assembly to adjust the WRD. Couldn't get two wrenches in there so to avoid taking it apart, I just put a whole different spare assembly on. Engine running much better now and no WRD suction at temperature. Slowly getting there. Anxious now to see what the fuel/air mixture meter tells me.

p.s. Had checked the thermostatic device with the protruding rod previously in a pan of 185° water and it was performing as it should.

[wwheeler]

99+ percent of members should stay away from thinking about adjusting the white and black screws on the fip. 

I would say like 99.7% which includes me!