Fast idle cam setting on 1986 1/2 D21 hardbody with Z24 TBI

[HRH]

So I've been working on Ray's truck, a fellow I know. Put a heater core in this hardbody last year. Did some ignition work to it early this winter. I've had it for a bit now diagnosing a hard starting issue. Rebuilt the throttle body, and found a temp sensor plug had broken off. Fixed all that, starts and runs great, but still had a little idle oscillation I didn't like. Very slight, about 25-50 rpm higher and lower for about 10 seconds or so each range.

 

Went nuts with vacuum issues, solved most of that, still have one more warm up test to do after she cools down, but found one last vacuum leak. Not entirely sure the idle fluctuation is a vacuum leak though. What I also suspect is the fast idle cam is out of adjustment. If it was a carb, it wouldn't matter, but it has the tps on the backside. The whole thing is rather goofy. Like a carb on steroids. :)

 

I was hoping someone on here might have a FSM for an 86 hardbody with a Z24 TBI system and could tell me the proper position of the fast idle cam. Or maybe you've done more of these systems than I have and you just know it! Most carbs it's supposed to be on the second step to my understanding. Of course normally I just had an electric choke and there was no fast idle cam.

 

Here are the pictures: Note, in these pictures, engine is at operating temperature.

 

 

The system is a coolant actuated plunger/thermostat type deal. It's actually kind of slick for 1986.

 

A. Fast idle cam adjustment. Moves idle plate forward or rearward in relation to round stud/peg attached to throttle half moon.

B. Fast idle plunger/thermostat dingus.

C. Round stud/peg that rides on fast idle cam. Have marked lines in white on fast idle cam indicating settings I would think.

D. Fast idle cam arm/peg adjustment. Moves the stud/peg that rides on the cam up or down away from or closer to the cam.

E. Regular idle speed adjustment for throttle half moon.

 

Note in the picture, this is at operating temperature, and that's where the fast idle cam is, right at the edge of the second step. The leads me to think it should be closer to the second mark.

 

 

Here's a better view of the whole setup. A little blurry on the bottom, but you get the idea.

 

 

What's the diagnosis? Am I over-thinking it? Should it probably be on the flat secondary when at operating temperature? Seems like I'll have to make a rather large adjustment to reach that spot, which is why I'm wondering if that's correct or not.

[datzenmike]

Idle should be 900 RPMs +-50RPM. If the idle is good forgetaboutit.

 

 

 

B is for increasing the idle when the air con is on?

[HRH]

Yes, but I want it perfect. If it was mine, I wouldn't care so much. :) Besides that it has that damn plug in coil that you can't hook a tach/dwell meter to, unless you make a jumper connection or use the special tool or have a cool photo tachometer. I almost bought one at work today, but it's rather expensive for just one time. Everything else I have has tachometers.

 

Forgot to mention, it idles too high on cold start up, that's another reason I want to fiddle with it. Has a bit more oscillation coming off the fast idle cam too, when it's about half warm.

 

EDIT again: You know, it's amazing how you can look at something and completely miss it. I do need that to be on the second step, because it stay on high idle far too long, but if it were half that distance, it would be just about right. Hmmmm.

[HRH]

Shit, now I feel stupid for even posting this thread. Think I've been sucking too many fumes in the 510. :blink: The one mark is cold, the other is hot. Simple simple simple. Feck!

[HRH]

It occurred to me afer waking up this morning the reason it needs such major adjustment is probably because of the age of the original unit. I imagine the plunger doesn't push out near as far as it use to, or it use to run hotter. Suppose I'll just have to deal with that since I don't think I'm going to be able to find one of those, probably not even at Nissan.

[HRH]

The best part of posting this up was realizing I can find the original idle point by probing the throttle switch for continuity, so that will give me back the original idle point.

 

And then I just realized that's why my 510 with the 200sx EFI runs so rich on warm up but is fine after. I had the throttle switch pins at idle, but moved it way up into midrange since the car didn't want to idle at 400 rpm due to the overlap of the cam. So now I have two little projects to do. The 510 runs fine because the three position switch still has midrange and full throttle. However, the idle and warm up will probably improve if I rotate it down just enough to make the third position of "idle." Freakin' sweeet!

 

Technically it doesn't matter except when it's cold. I've noticed that when it shuts off, if it's warm, no problem starting up, but when it's bone cold, it helps to throttle it to 3000 rpm on startup and hold it there to clear out the bugs, then it holds idle much better. Which I imagine is because I have it idling on a midrange setting, instead of the idle setting.

 

It's amazing what a night of sleep can do for the thought process! ;)

[HRH]

Ah hah!!! Was digging through another part of the manual and finally found the information I wanted!!!! :P

 

And here it is, in case anyone else wants to do the same thing.

 

[Creepy Cruiser]

So Matt, I think I should just drop off my '87 HB with you for a while, so you can go in and fix all the little tiny BS things it has, that I've just over looked for the last 15 years that I've owned it, lol. (jk)

 

btw, did you fix that speedo?

[HRH]

Hey, I did fix that speedo, thanks for the tip! Took forever and a day, driving around in the cold with the GPS hanging out the window, then checking speed, haha, it was great. Amazing how many positions you can put it in that aren't accurate! This truck still has some idle fluctuation, but I'm attributing it to being a 180k truck. Got it as good as it's going to get anyway. Runs pretty well.