A/c finally correct !! High idle question....
 

Thanks to Sixto for the diagrams and 3 weeks of going back & forth to it, it's done. Original problem was I had air from the defroster no matter what button I pushed. All 5 diaphragms are good. I found 3 bad switch-over valves, returned the vacuum lines to their correct routing and restrictors are back where they belong. Evacuated & recharged the system late today so I'll see tomorrow how cold it gets but I finally have air from the vents. I also disassembled both control heads (previous owner gave me an extra) and resoldered them.

Next issue to tackle: The idle seems to pick up once operating temp is reached. It sounds like something switches and the idle pops up to almost 900 rpms in Park. Is there some kind of thermo-switch or can I adjust it down somehow ?

anyone ?

When the idle kicks up, disconnect the throttle linkage from the IP. If the idle drops, something's binding as the engine gets to operating temp or you have very tired engine mounts.

Maybe something goofy with your cruise control?

Sixto
93 300SD 3.0 - comatose

high idle
 

I have the same problem and no answers, I posted a thread but only readers and no body has a clue, I have had this condition for some time and thought the last thing to check was air leaks but that was not the problem. btw, does your idle drop at any given time with no rhyme or reason and will also pick up without notice. Let me know what you may fine.

Peter

There's no electronic control on the 617, so, either the IP curb idle is too high or the linkage is binding.

As Sixto mentioned, disconnect the linkage from the pedal to the IP, as close to the IP as you can, and see if the idle drops down. If not, then make a curb idle adjustment.

The curb idle screw is on the inside of the IP. It's a long screw and is secured at a small protrusion of the IP with a nut. You'll need a long socket to reach it. The danger here is that the nut has not been moved in 20 years. If you put a bunch of torque to it, you can snap off the threaded lug on the IP. It's been done before. So, make sure you spray it down with Kroil or PB for several days before you tackle the job. I always prefer a touch of heat as well. Do not force the locking nut.......whatever you do.

Once the locking nut is loose, you can turn the threaded rod to adjust the idle speed.

Peter, you must really be desperate if you're checking for air leaks. There's a big one called the intake manifold with no throttle :)

Seriously, when the engine's idling high, unplug the round device at the rear of the IP. This will disable the ECU's control of idle. If idle drops to 500 rpm or so or the engine stalls, something's goofy with the ECU. The idle trimming selector doesn't have the range to support 900 rpm so I expect neither does the ECU. That's why I think it's a mechanical problem. But maybe corrosion in the selector increases resistance. Who knows...

Sixto
87 300D

Well, that all depends if he's referring to his own vehicle..........or the newer vehicle with the 2.5L driven by the GF..........????:confused:

True. My mind still doesn't comprehend air throttled Diesels.

Sixto
87 300D

high idle
 

Hello guys,
I am refering to my 617, which is also in the sd that this post was about, yes I have checked for binding linkages but none were found , and they are all new sockets, still a mystery after it gets to normal operating temp, will recheck links again, I feel it could still be something in the ip after it has had a hot soak for a while, or a some what of a long run, either way it only does it after it gets to operating temp.
PS. there are no electronic controls on my ip.

Peter

When you say that "something switches" at normal operating temperature, is it possible that its the aux fan comming on and could that somehow mess up the idle? No real clue here just throwing out an idea.

- Peter.

Not at all. The fan does not come on at 82C. Linkage is all fine. It will idle around 750 rpms no matter the ambient temperature until the 82C area on the temp gauge, then "POP!!" and it's idling closer to 850-900 rpms. It's not really a big deal. I have other issues to attend to but it just strikes me as not being right. I don't spend lots of time idling so I doubt it's effecting my mileage.

Can you tell if the idle speed is actually increasing, or is it just the tach reading? Last week, when I was driving around TX with a bad alternator and a dead battery, I noticed that low voltage causes the tach to read higher. Just a thought.

I think that an increase in idle speed when the voltage output is low is an actual clever design intent.

The idea being to increase engine idle speed to compensate for a low output voltage from the alternator.

high idle
 

Just as advisorguy says, its that quick,and all of a sudden your at least 200rpms higher, and yes the rpms are higher and the engine is definetly runing higher.As I said in one of my threads, I think something is happening in the ip without any outside help. Advisor guy, what viscosity oil do you use, I use rotella 5w-40, I wonder if it may be to thin for the warmer weather.
DOES ANY OTHER 617 OWNER HAVE THIS HAPPEN TO THEM, LET US HERE FROM YOU, THANK YOU.

Peter

On my 617 it's just the tach reading that changes, not the engine speed.