67 250 sec fuel injection idle problem

[john ogilvy]

Hey everybody! My 67 111 has the 6 plunger mechanical fuellie system.The engine will pull from a slow creeping speed to full throttle as smooth as butter, never a miss or a hesitation. The problem comes when I come to a full stop and the rpm's drop to around 5 or 6 hundred and unless I give it a little gas the engine wants to die.This only happens when the car is in gear(4 speed auto). In park or neutral the idle is around 1000 rpm. The question is, what are the reasons for this. Like I said unless I'm stopped with the brake on and in gear the engine is fine. Hope that someone has had a similar experience and worked it out. Best regards, John Ogilvy,Triangle Section Hosting Star Tech "05"

[Tom Hanson]

Check the throttle switch on the forward end of the intake.

[ja17]

Hello,
There is a sequence of items to check. The car must be in good tune. One good simple place to start is the fuel filter. A sufficient fuel supply is critical. If you have no history of when it was changed last, it may be a good idea to start there. It may also be nice to have the compression recorded to make sure everything is up to snuff. A fresh set of spark plugs would be nice before getting into the other mechanicals.
Normally the idle in gear should be around 650 to 700 rpms. Out of gear the engine should not increase more than 50 rpms. The ignition timing and its vacuum mechanism can effect idle. As Tom Hanson mentioned, the injection linkage is also critical and the stop screw on the venturi is also critical. The linkage is a good place to go next. If you view the intake venturi you will see a 10mm locknut with a slotted screw. This is a factory setting and is often mistaken for an idle adjustment. This adjustment must be set to just barely keep the butterfly valve in the venturi from binding. The linkage must rest against this stop during idle. The linkage rod going to the injection pump should be 233mm in length from center of socket to center of socket. This linkage should also be against the stop on the injection pump at rest. If this all checks out ok there is a large slotted idle air adjustment screw and and an injection pump idle mixture adjustment we can turn to next. Keep us informed.
Your car may also be equipped with an idle increase solenoid. Is yours an automatic?
Joe Alexander

[GeorgeMurphy]

I got this from Richard Gale, Santa Fe NM years ago - worked for me on a 230SL:

A worn fuel injection pump thermostat almost always results in a much
richer idle, when was it last replaced? And it it was, did they replace the
small washer spacers beneath the housing? Additional spacers will result in a
leaner idle. If the thermostat has been replaced, and if the aneroid
compensator has not been removed, and if you are absolutely certain that the
cold start valve isn't leaking. (to check, bring the engine to full operating
temperature and remove the tiny hex bolt in the side of the solenoid to see if
any fuel appears, if so, then the valve is leaking.

The last resort, after you check to see if your linkage is all adjusted
properly, is to adjust the idle richness at the rear of your pump. Always
make certain that the engine is turned off before making this adjustment. I
would turn the idle knob three turns counterclockwise then check the richness
at idle. You will probably need a CO meter to do this. The specifications
are all in the factory workshop manual.

If you want to check relative richness, here's a simple way to do it without
meters. After satisfying yourself that it isn't the thermostat, aneroid
compensator, linkage adjustments, etc, detach the linkage that connects the
pump to the cross shaft at the cross shaft. Push the linage down as if to
raise the idle. If the engine speeds up, the idle is lean, if it starts to
stall, the idle mixture is rich. To confirm, increase the opening of the
throttle, if the idle increases, then the idle mixture is rich, if it stalls,
then the mixture is lean.

I've never lived where a pre 70's car was required to pass any emissions test,
but I agree with George, MOST 280SL's have a cold start that is inop or out of
spec. Easy test, remove the 1 1/2" dia air cleaner on the back end of the fuel
injection pump, start engine (cold) and put finger over hole for the air
cleaner. Does it suck on your finger (good), remove finger and let engine run
until it gets to operating temp, checking for suction periodically. The suction
should get less as the engine warms up, and suction should be zero at
operating temp. Report result of this test and I will advise what to do next.
Also check the air cleaner while it is off.