280CE stalling problem

[Tristar1959]

have a transient very occasional problem with 78 280CE/M110:
After a high-speed run, such as coming off interstate, when coming to a stop, such as at a stopsign or light, immediately after the high-speed run; engine idles low and may stall out. However, it will immediately start up again. Problem does not appear at any other time, and all the basics are set up well (timing, mixture, etc). Did appear somewhat more frequently in summer, but latest occurred at OAT of 40F/5C.
Had considered possibility of vapor-lock, since this model is early, before the A/C -line-cooled fuel lines mod, but it will restart immediately.
It has the fuel pump checkvalve mod and a new accumulator and fairly new filter - and runs extremely well at high demand throttle settings, as well as usually at idle, so can't be a starvation problem.
Any ideas/experience with this, out there?
Also, has anyone retrofitted the later cooling lines mod into a 78 - could probably find the parts on a junker 280E or CE somewhere...

[300SDog]

And the air filter is recent or rotated often? Another item could be valve clearances on the twincam, intake valves too loose. Noticed with my 280/8 that valve clearances were critical for performance. And camshaft lobes eventually wore down at about 160k miles to where the valves werent completely opening, making it tough to start from stone cold and causing occasional stalls. Gotta love the 280 twincam engine, but must keep an eye on cam and rocker arm surfaces for wear.

[NKowi]

Check your fuel pump relay. I had a very similar problem with my `85 M110 Euro. Traced it to the relay.

[Tristar1959]

Air filter good, relay #21 working well and problem persists with swap-out, valve clearance recently set to specs, timing chain shows no stretch, mixture set to optimum, timing to spec minus 3 deg (trying to stay with midgrade petrol without pinging/"pinking".) All vacuum lines/systems good.
Occurs to me that it may be running too RICH rather than too lean/starving -
although CIS Airflow plate seems to operate normally and dashpot is responsive (at home, not out on road), I wonder if maybe after extended run at high air volume intake it isn't returning fully to near-closed at idle; because it starts up immediately (arguing against vapor lock and starvation; and cold start shouldn't be injecting then, either), but plate has had a chance to move closed again without airflow, and be sucked open, upon cranking. Had a hot START problem back before I replaced the accumulator, which is a starvation problem, but that isn't the case with this...call this a "hot IDLE problem".
While feedback from the daughtergoddess isn't always diagnostic, it appears that "butterflying" the throttle may head off the problem, kinda like "clearing its throat" (she's a nursing student, okay...?)
Maybe I'll take a feeler gage and solvent to the outer edges of the airflow plate and plenum throat - in the meantime, keep them cards 'n letters coming - this is a wierdo, and any ideas are welcome
Also, this may not be a M110 problem only - any CIS experience may be pertinent
Thanks All,

[Tomguy]

Sticking mechanical advance?

If your mechanical advance sticks, it's going to be way too advanced for the idle and that could lead to the stlaling. Once it stalls, the mechanical advance has nothing making it advance and it springs back to the nonadvanced position. Keeping the revs up (or adding more gas) by bliping the throttle would keep it from stalling.

Try putting a drop or two of oil on the distributor shaft (on the inside where shown). Make sure the shaft rotates clockwise freely, it should also go back almost fully on its own, it might need a bit of help. See if both occur correctly.

[ctaylor738]

I wonder if your EGR valve, or its controls are not behaving right. My theory is that after a long period on the freeway, where it would be open, it sticks and does not close all the way. That creates a vacuum leak and the car stalls. But then the vacuum is zero and the valve closes, no more vacuum leak, and away you go.

Try uhooking and plugging the vacuum line to the valve, and see if that changes anything.