sooo, now that i stripped my D-Jet of all un-neccessary addons the car idles considerably higher than before.
used to be a more or less steady 900 rpm idle.

first tought, "you got a vaccum leak somewhere".

so, i went to test for leaks using the "spray flamable substance on possible leak areas" test and listend to the rev's.
NADA anywhere, zero, zilch ...

now comes the strange part:
- car idles at around 600 rpm when cold, but doesn't die
- car idles at around 1100 rpm when warm and after long drives
- car idles at around 1300 rpm when really HOT !!! ( <- this is the strange part! )

when warm/hot and i hit the gas with the clutch in it rev's up nicely then falls down to almost dead (~400 rpm) then goes up quick to warm/hot idle (see above).
i suspect that is due to the removing of the decelaration valve, i guess the brains get's confused for a split-second until it catches up again. i can live with that but any input would be apprechiated.

also, when i turn the idle adjustement screw on the throttle body, i get a instant response in idle rpm. wouldn't a vaccum leak somewhere result in a slow/sluggish response because of fault air entrance into the system?

so, i guess my question is, if it's not a vaccum leak, what the heck is my engine doing?

i'm afraid to turn down the idle screw any further as the car then might die when cold or on decel (with clutch in) ...

D-Jet gurus please chime in.

oh, and btw. it's a 75 1.8 (without ANY smog-crap) running a '70 1.7 D-Jet system.
meaning, no adjustement screw on the brain for mixture!
Andy

PS.: parts removed or altered:

- no AAR
- no Decel-Valve
- Oil-Breather hose connected to Air-cleaner instead of thottle body cause i don't have the valve in the oil-filler box and the throttle body vaccum is too strong for a open connection to the case.

oh, forgot to mention,

the car runs GREAT, lotsa power for a little 1.8 throughout the rpm range.
spins easily over 5000 without hesitation ...

sorry for the long post above,
Andy

I assume you still have your AAR. But it may not be functioning correctly. 600rpm when cold is very low. My car idles at more like 1200-1500rpm when cold. If the AAR isn't functioning properly, then you are trying to compensate for that with a very low idle speed (when cold) and then a high idle speed (when hot).

Also, make sure that the throttle position sensor is adjusted correctly. If it is not sensing the throttle at idle position, then that could account for the drop to very low rpm's initially when letting off the gas.

I wouldn't worry too much about the difference in idle speed between being hot and very hot. D-jet is a primitive FI system. Variations in 100 or 200 rpm at idle is fairly normal.

Demick

Wait - I just re-read your post. You have removed the AAR. That is your problem. The AAR is really necessary. Your high idle speed is due to you having adjusted your engine to run at all when cold. Put back in the AAR, and adjust the idle speed when hot to 900 or 1000 with the idle speed screw. You will then get 1200 or 1500 rpm when cold.

Demick

but it's broken!

makes sense tho, thinking about it, trying to keep the engine from dying when cold would make it idle high when warm, wouldn't it?

Andy

Yep!

Andy,

I have pretty much the same idle issues. I have checked almost everything and still have them. One thing I have never checked is the distributor. Jeff B. told me the weights can get stuck. One of these days I will take mine apart, maybe you should check yours out and see what is in there.

For now, I just drive it. Like yours it runs great otherwise.

So, set your idle @ 1000 hot.

My AARs are all failed open, and refuse to close. I think the drop off is related to restricted air flow on decel.. take out the filter, and drive around the block hot a couple times.


M

Then it won't idle cold.

Andy,
You removed the AAR, so you have a low cold idle and a high hot idle. You could choke down your hot idle to 900rpm but then it wouldn't idle at all when cold. Not much you can do about that without installing a AAR or AAR type device. I would personally probably adjust for hot idle and use Nike idle adjustment when cold (makes you good at heel-toe work). The 200rpm difference between hot idle and really-hot idle I think is just indicitive of the old d-jet. I could never find a way around it. As for the idle 'bouncing off the bottom' on decel - well that's as you suspected - due to removal of the decel valve. The upside is that it cut's your shift time and proabably reduces wear on the tranny synchros because the rpm's drop faster when you close the throttle. I live with the diving idle because I think the benefits outweigh the funkyness. Two stock parts that get ripped out any time I'm around are the decel valve and the brake proportioning valve.

-Ben M.

So that is why I cook the clutch.... my decel valve is working!



yank yank yank


M

so get one of the ones from Brads shop that I stacked on the shelf

You don't need a decel valve. My car didn't even have one new (70-72).
My idle drops fine without it. No bouncing.

As others have posted, add a AAR valve so you have a good cold idle.
Adjust the idle "HOT" to 900-1000 rpms and then you should have a 1200-1800 cold idle.
bump the decel valve, I don't use them.
Do check the dizzy advance to smooth operation

Geoff

God you guys take apart the crappy AAR valves and fix em! Just take off the top to get to the inside to free them up or repair the heater.

Miles, you want to cheese with that wine?

Repair the heater? I have asked about the termination of the wire before.

I have a fucked one, let me know.




M

The red wire terminates at the bottom of the AAR valve and connects to the heating element inside. Does the AAR valve get warm to the touch if its hooked up to 12v DC ?
Twist the top off to look inside to see if the rotary valve is rusted open/closed.
Solution-soak with PB Blaster and turn with a screwdriver.

Geoff

Say Wha? All D-Jet cars are supposed to have an AAR. The wire is the only white wire on the ignition harness.

JB

Jeff, I meant the deceleration valve. The early cars did not have one. This is the valve that is mounted on the passenger side of the engine compartment and slows down the return to idle.

Andy,

Want to "borrow" my Megasquirt??

You should be able to get in hooked up and running in just a few hours

I'll be home this weekend if you want to pick it up and install it at my house.

now THAT is tempting

i'll call you later ...
Andy

Won't help your idle problem. You will still need an AAR or something equivalent.

Demick

Mike,

Do you still use the AAR or Decel with your MS (& details why or why-not)?

Thanks,

I didn't use the AAR, no need to, the MS has cold start fuel enrichment.

Car fired right up and held a perfect idle in 40°F weather, fuel enrichment disabled at ~300°F (CHT)

I don't buy it. You need more than just fuel enrichment when cold. You need more air as well. There are a variety of ways to get it: choke, AAR, hand throttle, Nike, etc. But you need something to pass more air when cold. If fuel enrichment was all that was necessary, then d-jet could have easily done that without the AAR.

Demick

If my car was running, I'd be able to prove it to you
I know, it should have more air as well, but it worked so I was not going to complain....IMHO, with a plenum design manifold, the cylinders have more available air to it than it needs at idle
(maybe I had vacuum leaks that helped while cold )


Also, the MS does not have a single aux fuel injector which is a bandaid in order to add more fuel, but instead, the extra fuel in injected at each cylinder in a more precise manner.

If you are referring to the cold start valve - that does nothing except help start the car when it is very cold. It does nothing for fuel enrichment during warmup. D-jet also does fuel enrichment during warmup by injecting more fuel at the injectors. But like I said, more air is needed too.

Getting a car to start up and run when cold without the AAR (or equivalent) is not a problem at all. But if it is tuned to do this, then it will have a very high idle once warmed up.

With the manifold intake design, the cylinders don't have more air than necessary (the butterfly valve is choking off the air supply during idle). If they did, then engine idle speed would be controlled strictly by fuel - which would mean that the engine is running extremely lean at idle. It would also mean that idle speed would not be accurately adjustable with an intake bleed screw - it would have to be adjusted by fuel - which (for the most part) it is not.

FI nerds of the bay area unite!