250 se coupe has engine problems

[124wagon_boy]

Iam trying to help a friend out on his what I believe to be a mechanical fuel injected 250 se coupe car.

It runs fine thru the upper power band but at idle and start up it hunts it goes high then low on the rpm.

I do not know if it is the injection but someone told me it maybe the idle air compensator or fuel pump or possibly the throttle body positioner sensor.Anybody have any clues.it is a 66 w111 coupe if that helps.

[bostosh]

Remote diagnosis and corrective actions are not easily accomplished.

First find someone who knows the motor.

Second powerwash and clean the entire engine compartment and front axle assembly.

Start with a valve adjustment, timing chain check, new valve cover gasket and finally a compression test.

next, new plugs wires points, cap and rotor. set timing.

change all fluids, gas air oil filters.

Only then, can you start even thinking about messing with the fuel injection system.
realize that this FI is a sophisticated analog computer and the last thing to go wrong. but it can.

Many of these cars suffer from neglected, deferred maintenance

.

[JJsAtoZatAz@MSN.COM]

the previous post laid out the basics for pre injector repairs. the 259se has a mechanical rack 6 plunger injection set up. when you first start the car it has a small nozel on the air horne which injects a spray of gas to provide combustion which has a history of failure. over time the injection nozle goes bad and causes over fueling and "loping" at idle speeds. i hear the part may be available from gus at pacific fuelinjection in so san francisco. 650 588 8880 he is a good souece for injector pump help gl Dave
have same car as you (my 7th one) and do all work on it myself (73 yrs old)

[renaissance_warrior]

Run a can of 44k from bg in a full tank. Drive that out, the see what it does. You have a varnished pump and injectors. BTW, there is not a throttle position sensor on that car. It is all mechanical.

[Grubeguy]

Does this car have a computer?

Mine's a totally different car with a different engine, but I had the same issue when I first bought it. I replaced all the vacuum lines and solved the issue. Good luck!

[renaissance_warrior]

No computer.

[UCF21]

Yes, has the car been sitting for any extended length of time that you know of, especially recently? That will help to narrow things down as well.

[wbain]

Think of the fuel injection pump as an analog computer.

[cadurning]

My '72 280 SE 2.8 engine just started doing the same thing with the idle alternating between a high idle and a low idle when cold. What I found is a small round sol valve that is mounted on the RF fender that clicks at the same time as the idle changes. That sol valve has a vacuum hose that is connected to the intake manifold. I suspect that there is a temp switch that controls that valve. My next quest is to find what switch controls that valve. Change the switch, solve the problem.

The car runs great and when in gear and cold the idle change in imperceptible.

[renaissance_warrior]

Typically that is the tubular thermometer in the tower on the injection pump. A very easy fix. It is for cold enrichment.