I am at a loss. Your AAR seems to be doing the job right. The initial low rpm does not make sense if the AAR is open (as verified) unless at the same time your regular air passage over the throttle valve is somehow closed more than it is supposed to when cold and after the car sits for a long time. I am guessing this may be the situation. You can take off the throttle body and clean it with throttle body cleaner and check for proper functioning and set the correct stops as well as inspecting it for wear. Also you can check the linkage to the accelerator pedal.

The only other electrical check I can think of for you to try is the Throttle Valve Sensor. It should be in the idle position at idle and causing the ECU to enrich the fuel mix more. To check: try the cold start again and when the idle is low and rough, disconnect the TVS... I am guessing the car will go lean and die.

I will check throttle body again. I am also going to pull the spark plugs after sitting over night to see if they are wet from fuel. Maybe an injector('s) are leaking. That would give an unstable idle until the plugs cleared up. Will post results later. I'm glad I am not the only one that is baffled by this mystery. I can also try disconnecting the linkage to the throttle body to see if that changes anything....showing possible linkage binding.

OK, here is what I did this morning. Checked plugs and none were wet with fuel. Disconnected linkage at throttle body....didn't change anything. I pulled TVS connector and it only changed idle slightly (almost not noticeable)...never died. So I suppose it is the next thing to check. I will check this before removing throttle body.

The car dying with the TVS was a guess. The fact it did change most likely indicates it was working. You can check the contacts visually by pulling the cover and you can also check them with a multimeter at the connector.

Do you have the dash pot on your z? I never trouble shot one but it seems there may be something mechanical involved so it could be that or linkage.

Philip

I actually observed the operation of the dash pot and it really doesn't seem to do anything. The "pin" that meets the throttle body linkage just slides up and down. It doesn't apply any force to the linkage. Im at a loss also. I have cleaned the linkage just in case it was sticking and operated the throttle manually with engine off looking for any binding and found nothing out of the ordinary.

To check the linkage you could also blip-stab the throttle for 1/2 second when starting to see if the rpm's rise on release (as opposed to the 10-20 second pressing mentioned above).

That was the other thing I did during this mornings test that I forgot to mention. I bliped the throttle a couple times to see if that would do it but it didn't. Had to manually raise it for the time mentioned above. Remember back in the days of carbs and you had to throttle it up a little just long enough to get it past it's "coldness" so to speak so it would idle on it's own? That is what this is like...maybe not as bad.

Philip, In post #53 I mention the dash pot really doesn't seem to do much. After looking at ET-9 of the 77 FSM it explains that the dash pot is adjustable. But to me it seems that if I was to adjust the dash pot it would allow more air into the intake. On cold start with the throttle closed what difference does this make? I'm confused now. Oh, I took the dash pot off to see if there were any changes....none. You would think this would be something easy to find.

Bob.

Edited February 7, 201213 yr by rcb280z

Do you hit the brake pedal when you start the car? I am wondering if it is the BCCD? We seem to have ruled out the main items.

Thought Review: The only way to change engine RPM that I know of is:

timing and air (assume fuel would bog it out for now)

If we rule out timing (for now) then the only devices/adjusters for getting more air into the manifold are:

1. Accelerator pedal and linkage to throttle valve

2. Throttle valve stop screw

3. Idle speed adjustment screw in throttle body

4. AAR

5. BCCD

6. leaks

7. Dash pot hysteresis

8. Drive line drag

A sticking AFM flap could also limit air flow but it is not likely given your blip test which would kick it in the pants.

So we are left with BCCD,drag and leaks since you checked everything else. If we rule out drag and leaks then BCCD is the one.

Next time you start,do not hit brake, or hit brake or punch brake (you know what I mean). Se if it affects rpm. Aslo reach under BCCD and turn the adjustment to see if it makes a difference.

I am grasping at straws.

Philip

Ok I will think about this as well. I know that if I disconnect BCDD the idle raises about 100 rpms. I'm pretty sure that it shouldn't raise the idle any right? So maybe there is something there. It didn't seem to make a difference when it was cold "cold start" though. Philip can you look at your throttle linkage and see if the linkage actually rests on the set screw....mine does and the FSM shows it resting on the dash pot shaft. FSM shows a 1.9 mm gap between the throttle linkage stop and the dash pot shaft. Sorry, not sure what you mean by "don't hit brake".

Bob

Damn Philip, I just read (again) in your post above where you asked me if I hit the brake when I started the car. The answer is no. I have been starting it from outside the car lately. I don't know why I didn't understand your statement "don't hit the brake". Must have been the lack of coffee this morning.

Bob

I'm now (thanks to Blue) intimately familiar with the inner workings of the AAR, and I don't think that's where your problem is. I'm new to the details of the FI stuff, but here's my theory...

From the instant you start the car, you are running lean.

When the engine is warm, it doesn't matter as much because the warm engine is more tolerant to a lean condition. But while the engine is cold, it's less tolerant of the lean condition and it causes your idle issues.

I'm thinking that it's so lean that even a cold (open) AAR isn't enough to bring the idle up to the 1200-1400 that you would expect on a cold start. Your foot on the pedal for thirty seconds FORCING a high idle is long enough to shake the cobwebs out and raise the engine temperature just enough that the AAR can now succeed and continue to hold the idle up where it should be.

That's why blipping the throttle while cold doesn't do much, but holding the RPM's up at 2000 for thirty seconds does.

I think you nailed it back in post #55 when you compared it to carbs where you "had to throttle it up a little just long enough to get it past it's "coldness" so to speak so it would idle on it's own?" I think that's exactly what's going on. Your mixture is off and your engine is really struggling when cold.

Have you checked for vacuum leaks? I'm thinking something like maybe the intake manifold to block connection. Severity of the leak may even reduce some as the block heats up...