Car's a 1984 XJ6 SIII, EFI. "Late" 4.2 XK engine.

Long story short: blew a head gasket. Sat for five years in a garage. Finally pulled the head. Turned out to be warped. Replaced with low-miles junkyard head. Everything put back together again. Mis-fire. Pulled head again. Bent intake valve. Replaced. Head back on. Everything reconnected. Firing on all cylinders. Oil pressure good. Water temp just above 90 and holding. Everything seems okay.

Except that it's idling high. In park or neutral it's about 1,600 RPM. In gear (foot on brake) it's about 900.

Ideas on what could be wrong? I'm out of my area on this one.

TIA

 

-Throttle mechanically stuck open a bit? Check cable and attachments

- Aux Air Valve stuck open, either mechanically or the electric plug to the heater is disconnected, or the internal heater isn't working

- Hose to AAV is broken/leaking, admitting extra air just as the though AAV was open

- Idle speed simply needs readjusting via the air screw on the Air Distribution Block
Idle Speed Adjustment

- Timing is way advanced, giving high idle speed

That's all I can think of at the moment. Others will chime in

Cheers
DD

 

Thank you very much! I will check those out this weekend.

 

Pretty well covered. I can only add a vacuum leak somewhere.
First suspect. Under the intake manifold aft.


Use of a vacuum guage might help.


And, unhook the cruise cable and throttle cable. If the idle settles down., one or both are sticky.


Carl


Carl

 

Will do.

 

Along time ago, we owned many of these new.........
Its sounds funny but check your FLOOR MAT......That's the reason they all have hooks on the floor now.......
GTJOEY1314

 

Does the car have the factory labels under the hood? It tells you how to adjust idling speed, also shows a vacuum routing diagram.

 

More to consider:


Reduction of idle speed by applying the brake with the transmission in a drive gear is normal. Not a good thing. Known as "power braking". Used by drag racers to load the converter and get a faster take off.


Start by ID of all vacuum lines and pinch off or plug one at a time til you find one that is leaking.


Then if still "racing" start the other stuff.


I like the floor mat suggestion. Surely, an easy. When Toyatas were "running away" that was a lead theory...


I've been there on other critters.


Carl

 

1984 OR so there was an actual tech bulletin, remember audi back in the day.
The pedals on the jag were on an arm not from the floor up. If the rug got jambed it would race. Theres a 1,000 mile original owner vpd black with cream in Georgia, same thing.
Mechanially, you had the head off, make sure there are no vacuum leaks,
Good luck
GTJOEY1314

 

Thank you to everyone who replied. I've been quiet because I didn't want to post over every little thing. That and trying not to ask questions for things I could find by searching the forum.

Carpet mat is okay. Butterfly valve gapped okay. Throttle body is clean, but went over it again anyway, along with the spring mechanism and the cable to make sure nothing's binding.

Found a small hose that was disintegrating and had a tear--replaced. Found another that wasn't holding a good vacuum and replaced that. The others checked out okay.

Found an 85 in the local yard that was mostly complete. I diagramed the vacuum hoses, and with the octopus that connects to the distributor to various things, tagged all the ends and pulled it, bought it, and brought it home. Verified I had all my stuff plumbed the same way, and in one case made a correction.

No difference. If there's a vacuum leak I can't find it.

I've been struggling to find the idle air adjustment screw. Saw it mentioned numerous times but couldn't locate it. Finally found a photo (thank you, David Boger) here, and was able to locate it on my car.

Everyone's right--that's a PITA to get to. The MAF box is in the way. I made a preliminary stab and getting an allen wrench on it--I can get it in the shaft but not seated on the screw head. I'll come back to that.

So that's where I am. I'm certainly better off than I was a week ago. Just not there yet.

 

you need an allen wrench of a certain length, and it needs to be bent a certain way, a normal "L" allen wrench will not work.

I have one of those which was given to me by another forum member years ago, I will try to make a drawing of it with measurements.

Also be sure you don't have a sticking throttle cable. If it requires force to press the gas pedal, chances are it is sticking.

 

Allen head screws!!! Generally, I like them. Far better than slot headed!!!


I've been on an extended fix of my band saw. Not unusual to me.
Swapping in a new blade is supposedly easy ad done by craftsmen
regularly to suit the need at hand.


Tis an Asian made unit probably of HF origin. I bought it quite used a
couple of decades ago. Hundred bucks. It has served me well. Last time I did a blade swap it was easy...


This time, I decided to tune it up. Rubbing block alignment, spacers, etc. Multiple Allen heads.


I've a huge selection of tools to deal with the. Best. T handled and socket headed.


But, one defied all of them. Access restricted. My socket tool got it.


Another required a neat busted bolt extractor. Splined.


Clue:


I read of this one. If one uses the usual "L" shaped tool and it takes the log side for reach, that leaves the short end and limited torque to twist.


Use a bit of tubing. Drill a few holes. Join the to make a slot. Insert the short end. Secure with weld, solder or JB. New tool !!!!


Carl

 

here's the hood labels from my 1984 model year, build date of June 1983