I'd look for vacuum leak, since idle is normally not affected by poor fuel supply. When engine is starved of fuel, it would show at higher rpm first, since then motor needs more fuel. I would check simple things, like:
1. engine temperature sensor, it is located close to left thermostat housing and has connector plug similar to fuel injector. Check resistance of it on cold and then see where it goes at a full warm up, it might fluctuate and cause fuel supply to go up and down.
2. Unplug one of vacuum lines, when motor is warm and see how it changes idle behavior.
3. last and not least, check AAV valve, this is a bit tough one, however if AAV valve is bad, or sticky, they are hard to rebuild and impossible to find new anymore.

 

Thanks, I found it.

 

Bingo

 

Correct as you are. I have the red one.
I put this all back together yesterday after 4 months. Cleaned everything etc.
Same issue. Racing up after trying to settle to it's proper idle. Where is that auxiliary air thing?

 

The auxiliary air valve or AAV is ths idle control valve, it is located at the rear and below the LH intake manifold, it sucks air from the back of the LH air cleaner. If you remove the filter element you will see the hole that should have a pipe running to the valve.

If the valve is not operating correctly (ie stuck open) it will cause erratic or high idle. Put you finger near the port in the air cleaner when the car has walmed up and there should be little to no air flow.

 

I feel like a fish out of water, but I' going to try.
I have posted 4 pics. The hose coming out of the LH air cleaner as you see, goes to...nothing? It was just as I show it. The piece going into the air filter housing that is just hanging there is also attached to nothing within the air filter housing, is that the AAV? Or is the AAV the unit you see that is under the air filter housing? There is a port on the side you can't see, that has nothing attached to it as of now. Any direction will surely add years to my sanity.

 

That's the RH side you want the other side

 

LMAO! Yes, you are correct. I found it.

 

I do not think the later cars with pump in tank have a sump tank, unlike the pre facelifts which do. But I agree the symptoms do not sound like fuel starvation.

I am a bit unclear about the exact trouble. If the car starts OK, and idles in neutral at about 1000 to 1200 rpm, and then after a bit the idle climbs, and then the engine drops to a lower rev, and then rises to a higher one about 1400 and goes on like this, then it is just about certainly the Auxiliary air valve. If the problem disappears once the car is up to temp, then it certainly is. Here is a photo of the AAV (induction manifolds are off on this photo):


It is under the cabin-end of the B bank (US driver's side) air filter box. If the symptoms are as I describe, the reason for it is the over-run cutoff system of the ECU. When you are blasting along the road and have to lift off, the ECU cuts the injectors to save fuel until the revs drop below 1400rpm. If the car idles too high (because the Aux air valve is not operating properly to adjust the idle revs down as the car warms up) the ECU over-run cutoff cuts the fuel, only to restart it again as the revs drop. Hence the up and own revving.

New ones are available, but there are very dear. It can be fixed sometimes, see The Book, or some people have replaced it by a manual system.

 

Good one Greg a photo is worth a 1000 words

 

You guys are the best, Thank you. I read all I could on that AAV in Kirby's book. Great stuff. I put that TPS in wrong which is now keeping my car idiing at 1700 in park when warm. It has also triggered a FF 17, which is logical. Until I get that TPS back to where the car was surging, I'm not going to attempt any adjustment on that AAV. You can be assured I'll keep you posted.

 

And some people remove 'em entirely and do without.

Cheers
DD

 

Doug

Any problems in cold weather?

 

Never tried it on a V12, myself...but others have.

My own V12 had a dead AAV...no high idle. Never had a problem except on the very coldest mornings when it was necessary to use the accelerator pedal to increase engine speed for 15 seconds or so

I worked on another V12 with the AAV stuck open and it had a restrictor in the AAV inlet to bring idle speed down. Worked well. Again, no high idle for cold running but it didn't seem to be a problem except on the very coldest mornings. The distributor vent system had to be reconfigured, though.

Once I ran an XJ6 without the AAV installed for about a week in winter. Again, no cold running or starting problems. In that case, though, the base idle had been tweaked upward about a hundred rpm or so.


Cheers
DD

 

I'm pulling my hair out trying to set this TPS to its proper setting.
Can you point me in the direction of the correct process to do this please.

 

This is what I did:

Remove the throttle actuating rods from the capstan. Remove throttle cable from capstan. Unbolt the capstan from the V, the spring in the capstan will hold it in the throttle closed position. Slightly loosen the screws holding the lugs of the TPS to the capstan underside, so the TPS body can be turned with a little effort. Hook up the voltmeter (+) to the wire that gives the variable signal back to the ECU (easiest done at the plug) and put the other (-) voltmeter wire to earth. Turn on ignition, adjust TPS position to give 0.32V. Tighten TPS screws, reassemble capstan to V.

Hope this helps

Greg

 

It does help. Here is what I did. I have found that if that TPS isn't in it's correct position it will trigger a FF17. I finally got rid of that.

I have screwed in that AAV bolt almost to its max, the car did sound smoother, but it didn't lower my idle. In drive I'm at 1100 rpm with the brake on. In park It's at 1800
What's next?

 

A few things could cause this.

A leak somewhere in the intake system after the TB.

TB butterflys not adjusted correctly, there is a procedure in the ROM to set the at rest butterfly with a feeler gauge. I am at work so do not have my book handy with the value.

You could close both butterflys totally one at a time and see if this lowers idle rpm, the engine should just about stall with both closed, if it does not then you have a leak. I'll post the procedure when I get home, if no one else does so first.

 

Like Warrjon says, there is a leak into the intakes somewhere, or your throttles are set too far open!. It is possible, quite likely even, that the AAV is stuck open. The quick way to find out is to remove the B bank air box and filter, then stick a bung of some sort into the inlet to the AAV. This is on the cabin end of the airbox, and lets filtered air into the AAV which (if the AAV is stuck open) goes out the top of the AAV into the manifold, bypassing the throttles.

Good luck

 

The procedure is to insert a 0.002in feeler gauge between the top of the butterfly and TB housing then adjust the stop screw.