Any Thoughts Appreciated
 

A few posts back after a valve adjustment I reported that my ignition coil was ticking, '72 350sl, w117 engine.
I took member's reply suggestions , changed coil, coil wire, etc. .
Anyway it turned out that even though the engine timing was 5 degrees atdc @ 750 rpm , per book, the timing was too retarded. The ticking went away after advancing the timing to 15 degrees atdc.
The car starts up fine, but initilaly lidles very high, searching up and down for a constant cold idle between approximatelly 1200 and 1600 rpm for the first 3 - 5 minutes and then settles down gradually to a steady rough 750-800 rpm that can be best felt sitting the car and or listening to the exhaust missfires.
After warm up and shut down the car won't idle warm without feathering the throttle and accelerating the engine(as if burning off excess fuel?) which eventually gets it back to the rough idle mode.
Fuel pressure is good in run mode and holds as required after shutdown.
Temp sensors, cold start valve, trigger points, plugs, points, cap, thermal time switch new or checked out ok.
Sound like an auxilliary air valve malfunction?
I'm also thinking poor injector pray pattern, pressure sensor vacuum hose, ignition wire resistance problem


Thanks,

Knarf

"Anyway it turned out that even though the engine timing was 5 degrees atdc @ 750 rpm , per book, the timing was too retarded. The ticking went away after advancing the timing to 15 degrees atdc."

Don't you mean 15 degrees BTDC? If so that seems to far advanced. Did you unplug the vacum retard? I think it shoud stay connected when you are setting the timing. My 72 sl runs best at TDC or 5 BTDC when I am running premo.

Anyway is your 72 like mine with vinyl interior, roll up windows?

http://photos.yahoo.com/bc/darryl_hill_us/lst?.dir=/My+Photos&.src=ph&.order=&.view=t&.done=http%3a//photos.yahoo.com/bc/darryl_hill_us/lst%3f.dir=/My%2bPhotos%26.src=ph%26.view=t

Hill,

Thanks for the reply.
Yes, I think my car is the younger sibling of yours, #69 off the production line, US model., roll up windows, vinyl interior, manual locks.
It seems to be pretty much original, purchased earlier in the year from the original owner. I can't wait to get it running right and take the hard top off.
I did error in setting my timing. It's been reset to 5 btdc and idles much better cold, but I still have a rough idle and hard restart after warm up. Fuel pressure ok and seems to hold acceptably, trigger points clean, plugs, cap and wires ok.
New cold start injector. Now suspecting MPC unit.
Any similular experiences with your car or thoughts about my woes appreciated.

I have a rough idle to but I know that my distribiutor is beat to stuffing. How many miles does it have and how often did the PO drive it? You mentioned the pressure sensor vacuum hose, change it and be careful to get the right size. Sorry I can't be of more help but without seeing, it would be parts changing not diagnosing.

I need a little info myself. What RPM are you turning at 60 MPH? and does it have a posi?

On my 4.5 when I adjusted the timing after a valve adjustment I found that setting the timing to 5*ATDC (per book) produced poor running, run on and hard starts. While setting the timing I also observed an additional paint mark at 10*BTDC. I took a gamble, disconnected the vacuum to the distributor and set timing to 10*BTDC. Upon reconnecting the vacuum, timing was sitting about 2-3*ATDC and the car ran fine. Try setting to 10*BTDC with the vacuum disconnected and plugged. Reconnect and see how it runs.

For the manifold pressure sensor hose I found the 5/16 fuel line worked good. It fit snugly on the sensor, but loose on the manifold stub. A small hose clamp holds it tightly to the stub, but is a real PITA to get a screw driver on. Found my fabric covered line was rife with small holes, changing the line dramatically improved the running condition.

Hope this helps

Mike and Hill thanks for commenting.
The car is 30 years old and has only 92,000 miles. Service records confirm the milege. So the car was not used too often.
The MPU hose had been changed by the PO. .
I'm running rich, the plugs are uniformly slightly sooted and a little damp at the base of the spark plug electrode.
Per stevebfl's 3/30/2000 post I tried adjusting the MPU and have gotten much improved warm idling and restart. I'm not finished my adjustment but it looks promising.
When I purchased the car the PO told me that the last "mechanic" working on the car couldn't get it to idle correctly.
At start up it would idle extremely high until warm up. I discovered that the "mechanic's" solution to get the car to run without shutting off was to disconnect and plug the vacuum hose from the throttle valve to the vacuum switchover valve that regulates the distributor retard. So who knows what he may have done to the MPU besides replacing the hose leading to it.