So, I had to do some more work on the cooling system after some things started leaking that werent leaking before. Upon getting everything back together it wants to idle at 1500 and that is super annoying. Now, the water rails were among the things that I had to take apart and in the process of doing that I had a good look over of the hoses for the aav as well as checking to see that it was still functional and it appears to be so for the time being I am ruling it out as a probable cause. I have been all over the place in there looking for vacuum leaks and havent been able to find any. There is one mystery though that I am hoping to get some help solving so I can rule it out as the cause. On the front of the intake manifolds there is a vacuum port, on the A bank this port is capped, on the B bank there was nothing on it and it was shiny which tells me that something had been there. I can't find anywhere a vacuum line that I missed so I am hoping someone can tell me what is meant to go there so I can figure out either what I missed, or what I may have plugged into the wrong place. During the test running when it was idling high I had capped that port just so it wasnt a leak.

 

Hmm. If you're wrestling with idle and you feel confident the AAV is operating correctly, like sure sure, I would remove the air filter cases and REALLY make sure that the butterflies are set (both) to .002 thousandths...

I always do this, lol. My advise seems to always suggest an issue that I was just wrestling with, haha. And something I think I "learned"...in the process.

Seriously though. I am amazed at how sensitive the cars are to the setting of the butterfly valves...

I have a couple of plugged vac ports and my experience has been that a missing plug (seal them) doesn't have THAT a dramatic effect on idle... That's just me
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I will definitely look into how to check and set that clearance, I haven't done that yet and it sounds like a good idea. Though it had idled fine before, its possible however that in the process of fixing all of the other things I've been working on that whatever had caused it to idle lower before was actually an issue with something else that I've since fixed.

 

Put your finger over the hole and see if the idle reduces. Post a photo of the hole so we can be sure which of the many you are referring to.
But, it might be that you are referring to the vac spigot for the B bank FPR? If so there should be a hose to it from the FPR.

 

this is the specific port that I am referring to. I had it capped during the high idle and just removed the cap for the photo. My concern is that it might have been used as a source of vacuum for something important that got lost in the jungle of tubes and such when I took things apart.

 

Hmm. Thanks for the photo! But I'm a little lost. Then again, the ONLY XJS engine I have ever seen in person is the (US) 1990...

In the photo, is that the engine oil dipstick? Is this the end LH intake from the front of the car,,, or from the rear? I ain't seen everything by any stretch of the imagination, but I don't recognize some things as they are laid out in the photo.

But yes, if this is the front of the LH intake (towards the rad) I think Greg is correct in that that vac line is supposed to be connected to and CONTROLLING the fuel pressure regulator (FPR) that allows fuel to RETURN to the tank. This also relieves pressure at the rail. Not having this connected will create a larger vac leak than some of the other spigots on the intakes AND (because the rail is at higher pressure) will have the car run rich AND increase idle some.

If these suggested possibilities and questions are a little bit on the side of dumb questions (because in ain't seeing things rightly), leave them and wait for a more experienced person to talk about what that might be...

 

Please... Widen the shot of this QUADRANT of the engine bay, if you don't mind...?

 

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It looks like all the vacuum lines for the fuel stuffs are hooked up far as I can tell.

Interestingly, the butterfly plates were far away from .002, which is easy enough to fix and now it doesnt want to start lol. Also discovered while adjusting those that the bushings for the throttle linkage on both sides are just gone. Im sure that doesnt help matters and ordered some new ones. I almost 3d printed some but I think I will wait to test PETg in the engine compartment on something a little less vital.

 

Ok. I see now... The red line in the photo is where that vac line is supposed to go. Try that,,, well come back to the sensor on the fuel rail,,, the switch,,, and how that's hooked up later. I'll bet my pinky toe that the idle will normalize
The fuel pressure regulator works DIRECTLY with fluctuations in intake pressure and vac

 

JJJ, I think that in the case of the photo, the vac lines are correct, as the OP has a vac connected hot start gizmo in the fuel rail.

 

Hmm. Cool! My hot start switch was broken when I got my car. Then and since, the spigot that IS feeding vac via the switch to the regulator was routed directly to the regulator... I didn't know,,, and never questioned it. Thank you Greg!

In that case,,, is the switch opening and closing?

 

It is being very very stubborn about starting, like its not even trying. It will crank but im not even getting a hit and miss sort of firing. I need to spend some time confirming some things are still functioning like they're suppose to. Something in the ignition circuit im guessing isnt playing ball which is a new issue. Cant very well get on with troubleshooting high idle if it wont idle lol. Fun times.

 

For ***** and giggles,,, try connecting that vac line directly from the intake manifold to the fuel pressure regulator... Or, blow on/into the vac tube to see if the heat switch is allowing air/VAC to pass freely from the intake to the FPR...

 

yes, air will pass freely through that little switch thingy. I have discovered a potentially bigger problem though that I will make a new post for. I hope I am wrong though lol I would love to be wrong.

 

Unless hot that "switch" should allow clear passage of air. It shuts off the vacuum to regulator when hot thus increasing fuel pressure slightly.

 

For the no start issue, check the plug on the coolant temperature sensor (2 pin connection on the left thermostat housing). If you have been playing in that area, you may have knocked it loose. Mine was very brittle and one day it just wouldn't start. If that isn't the problem, Grant has an excellent document on no start issues in the Sticky Threads at the top of the forum.

 

Now that you made me think about that plug I am wondering if I might have mixed it up with the plug that goes to the air filter housing. They look the same and the wires are similar in length. That is a definite possibility. When it stops raining I will investigate that. If that turns out to be the case I am going to find a way to label those wires lol Im sure this wont be the last time I take this stuff apart.

 

I never did figure out what that vacuum port was used for, its capped now and with the butterfly plates set at .004 it will start. Its not happy about it, and the idle is still a little high at 900ish when warmed up. Definitely wont be balancing any coins on it but this is a good start anyway. now that its been let to run enough to warm up she marks her territory pretty good. Will get to spend some quality time fingering out oil leaks. Far as I can tell so far its mostly around the pan gasket. We'll see, I know theres a post somewhere about oil leaks, I'll have to go look at that next.

 

Ok. You're in a good place!
Just real quick,,, when you say capped it, what do you mean? Is there a vac line going to the FPR?

AND, if you run the car and plug the hose going to the AAV, what happens?

And, the gap, at least for the 1990, at/around the throttle plates is .002! A little more air makes a big difference at idle. No kidding.