After many years of sitting my 74 2.0 is now ready to rack up a few miles. Last weekend after having failed to get a proper dwell setting and seeing that my points looked pretty sorry, I installed a Hot Spark unit that I had bought years ago.

Now with fresh plugs, cap, rotor, "perfectly" timed distributer, cleaned injectors, a tested and functioning AAR and all new vac lines and hoses, TB gasket etc. My once very high cold idle is now nonexistent. Car will fire than die, then fire and catch surge ~ 500 RPM. Ambient these days is mid 70's here. When warm idle is also low ~700+-

Since most threads are to cure high idle, I'm wondering what sensors CHT? etc are responsible for cold idle enrichment that I can check for proper functionality. My idle screw adjustment seems to have very little effect and is already "out >1.5 turns which seems high. (what are others seeing?) My ECU is set 1 click rich from factory mark but I'd think I should be closer in RPMs before I muck too much with that?

Thx

There are no real sensors for high idle on a D-Jet system. There is only the Auxiliary air regulator. It adds more air to the system when the engine is cold. It is the round can located to the left and just behind the oil filler neck. There is a white wire going to it from the relay board. The wire powers the bi-metallic heater element in it, and that closes the AAR as it warms up. The same electrical circuit feeds the coil.

IIRC, there was supposed to be a resistor added to the cylinder head temp sender to alter the warmup curve of the fuel injection, so it ran richer for longer to improve the cold idle.

If your warm idle is too low, I would start with that. Get the warm idle speed correct before you mess with anything on the cold idle.

Confirm the start state of the AAR when it is behaving this way.
Is it open or closed?
Open will have vacuum on the filtered air side
Closed will not have vacuum on the filtered air side
Presence of vacuum will increase the idle speed, closed no vacuum will reduce the engine speed

surging? Does the MPS hold vacuum? Has it been tampered with/rebuilt?

74 is not supposed to have the cht resistor.
Cold start will be a combo of the cht saying the engine is cold, and the AAR letting all that air in (basically holding the throttle open for you).

In my experience a low idle at start could be that mps issue mentioned, that would be sending you really rich. The afr idle adjuster on the ECU could be in the wrong spot, that is easy to see.

All of my stuff works, so what I find really affects idle at start and warm, is timing. You say it is set perfectly for timing, are you sure? I assume you don't have points with that new/old system you installed.

I would start with making sure the MPS holds vacuum.

to test the aar just unplug it from the plenum and see what happens on a cold start.

If it idles cold when you open the throttle, and it idles fine warm, the aar is stuck closed

The cold start on the D-jet system is two fold and this is spelled out on Anders website.


The AAR is a controlled vacuum leak for a cold cold engine. The enrichment is enhanced at the MPS directly by the amount of Manifold vacuum and hence more fuel. This is controlled by a thermistor on the bottom of the AAR valve and after about 20 or 30 years of heat cycling...stop working along with the valve body seizing in the aluminum bore.

At really cold temps (below 32 deg) the engine is assisted by a fifth injector on the plenum.

The CHT is the enrichment for a warm crankcase cold head start.....which is basically an electrical thermistor which changes the injectors pulse width duration in the ECU.

The one thing Clay is right about....ASSUMING the static timing is correct is to set the idle enrichment and air bleed screws to the spec idle while the engine is in the warm warm cycle or both the crankcase and head temps are warm. This also ASSUMES that the CHT tests to spec.

Good Luck.

I can't speak to if there was a mid year change but my car seems to have a CHT. I'll Ohm it this weekend.



As mentioned in the original post I visually verified a working AAR and then ran carb cleaner through it and dunked it in an ultrasonic bath to further loosen things up. And ECU is 1-2 clicks rich from factory mark.


Factory 27% timing mark still visible and setting with a magnetic pick us vs points took less than a minute, sweet!

I totally spaced on the MPS. I'll read up on that and pressure test and report back along with warm idle.
thx

Note that the cyl head temp sensor should be on your car (needs to be), an added resistor should not be there if everything is stock.

If when pulling the hose off the AAR (the one that runs between it and the air cleaner) you feel a decent amount vacuum, then that is not the source of your cold engine/low idle issue. When it's warm there should be no vacuum (port is closed).

I wouldn't expect the idle screw on the throttle body would need to be out 1.5 turns when all else is good. That's seems pretty far.

The knob on the ECU will enrichen (clockwise) or lean out the mixture (counter-clockwise). The idle will surge if the ECU knob is set such that it leans out the mixture too much. If you can't take the surge out by turning the know clockwise (go slow, give the car 10+ seconds or so with each change), then the problem lies elsewhere. Doubtful that the ECU is the issue.

Let us know what you find with the MPS.

Misread that. Yep, no resistor.

Besides cleaning the AAR
Did you test it with 12v to see it open?

Unless there is another way to test it, yes.

Dug in a bit today. Temp sender in the throttle body specs out fine. The CHT ohms out fine at the ambient I may test again when warmer or just replace when I next have to have the tin or intakes off. I checked the CHT pig tail connection and it looked awful. I'm guessing the junction cover, just like the AAR unit was translucent at some point but had turned to sawdust inside so I removed it.




The MPS did Ohm out fine electrically. While not holding vacuum indefinitely, its loss rate was less than spec'ed in pbanders pages so I'm calling it good especially as most cite failure in a rich running condition which I do not have.

I also now se that my thermostat seems to have failed (open) with cooling flaps fully open. Now I know why it seems to take so long for oil temps to come up. This can't help my "warm idle".

Time to just run it into the hopefully nice fall weather and see how it goes.

Does the MPS show signs of being opened? (Screws instead of rivets holding the 2 halves together and/or no resin seal on the top where the full load stop screw is.)

I had the same problem. The timing was too far retarded at idle, even while being in spec otherwise. I was able to adjust the stop on the retard side of the distributor and that fixed it.

The MPS looks untouched down to the yellowe epoxy on the adjuster screw.
Unfortunately I was unable to test my CHT hot because suddenly I have no power! Backed the car onto ramps this am after returning from storage so I could adjust the clutch cable. After all my vacuum and sensor testing absolutely no power through the ignition to any of the usual suspects, oil, generator lights, FP etc. Seems it's always something. Though no previous signs, I may start w the ignition switch.

The MPS looks untouched down to the yellowed epoxy on the adjuster screw.
Unfortunately I was unable to test my CHT hot because suddenly I have no power! Backed the car onto ramps this am after returning from storage so I could adjust the clutch cable. After all my vacuum and sensor testing absolutely no power through the ignition to any of the usual suspects, oil, generator lights, FP etc. Seems it's always something. Though no previous signs, I may start w the ignition switch.

FOLLOWING..I have a 73 on the rack doing the same thing...runs good warm/hot but cold start never a fast idle or start on its own with out opening the throttle