Hi Everyone,

Last Wednesday, I was taking my daughter to an event in the '90 XJS (5.3), and we ran into an unexpected and unusual traffic jam. After being stuck in stop n' nowhere-to-go (no turns or cross streets available) for 30 mins, the temp started to creep above N.

Starting to sweat a bit and staring at the temp gauge, I took the first opportunity to get out of the traffic. We were 90% of the way to where I need to take my daughter, but could only have gotten there on small residential streets with lots of stops. Against her teary insistence that we continue, I said, "sorry Honey, but there is one thing you don't do with this car, and I've got to deal with it now."

Made my way to a street with a long stretch that I could get up to some speed without stops, then charted a course for home that could maximize my ability of returning engine temps to normal and avoid a hot shutdown. When, I pulled into the garage, temp was back within the N, and I grabbed the infrared and checked temps everywhere -- whew!

On the cooling front, checked everything and it's time for either a re-core or a new radiator.

However, yesterday I needed to pull the XJS out of the garage to make room to work on figuring out a power steering issue on our '95 VDP. When I started up the XJS it now has a rough idle it didn't have before. It runs fine at higher rpm and there isn't any new noise.

Before, I tear everything apart to R&R the radiator and possibly introduce new variables into the equation, what should I investigate or check to fix the rough idle?

Thanks.

 

I'm inclined to say that you might've over reacted to the increased temp reading.

It isn't at all unusual for the needle to creep up in a long traffic jam.

What were your infra red temp readings?



How rough is rough? A little tremble? Or bad enough to shake the car?

Might have developed a secondary ignition problem--- spark plug, plug wire, distributor cap/rotor. That sort of thing.

Might have an injector problem--- have they ever been professionally cleaned?

Listen to the exhaust. Does one side sound different than the other? Does one side sound smooth while the other sorta make a puff-puff sound?

Cheers
DD

 

Thanks Doug. Sorry I should have been more clear in my post, but it wasn't just an increase, after being stuck for so long, temp kept creeping up and was nearing the danger zone (half way between top of N and H) and rising. Return route allowed me to bring temps back down to normal so I could avoid a overheated shutdown.

Injectors were professionally cleaned about 5000 miles ago when I had the hoses renewed (the guy in Florida whose name escapes now).

 

OK, just had first chance to go out and start the car. When it first starts it isn't very rough, but after driving it a bit and getting up some in temp it begins to exhibit rough idle, but nowhere near as bad as before (weather was warmer then).

Left hand exhaust has odd puff puff note, but I also noted that once warmed it is idling at only about 350-400rpm. Had my daughter listen to the exhaust as I increased throttle to bring up rpm a bit, and the odd puff puff note goes away.

 

Drove the car a bit more late yesterday, and it is definitely behaving differently than before the incident.

Idle, once the engine is warmed up, is too low, and uneven.

Is there something from overheating that would introduce a misfire or alter idle speed?

 

the heat in the engine compartment might have overstressed one of the coils or wires... I pulled mine after an marrelli failure and sprayed all the contacts with cleaner and silicon spray... failure gone...


now I have a miss now and again after replaceing leaking injector hoses

 

Update. I replaced the spark plugs, wires, distributor cap and rotor this past weekend and the car now runs much more smoothly, though not perfectly.

The idle is low (if the tach is accurate) and drops down to about 300-400 in Drive. The funny thing is that if I try to adjust the idle at the AAV, it has no effect. I let out the bolt at least five full threads and nada.

I know a faulty AAV can cause high idle, but can also cause low idle?

 

It can, to the extent that turning the screw anticlockwise is not getting any more air get into the intake manifolds as it should. Why is the question; could be a blockage in the AAV somewhere, in the tube from the AAV. Why not remove the AAV and clean it out, lubricate plunger, unscrew the slow running bolt completely and clean out its air passages etc?
Grant Francis has a brilliant method of taking the AAV completely to bits and fixing it, which I have bravely just done a few days ago, it is an absolute cinch.


Greg

 

On the cooling issue, did the Aux fan come on ? (And the temps were still rising?)

 

Yes the Aux fan came on. It needs an new or recored radiator which is this weekend's project.

 

Dumb question, but are the two hoses that go into the AAV air lines or coolant lines?

 

They are Air lines.

The AAV is controlled by the heat from the cooling system, The valve opens and closes to control the amount of extra air going into the engine.

Mark

 

Caution is the key. heat and alloy or partly alloy engines just don't get along. don't ask!!


You can limp along with more safety by popping the bonnet and allowing better air flow. In really tough situations, turn on he heater and open the windows. keep moving if at all possible. Stopping just cuts of the cooling. The auxialry fan does help though.


The Injector guy is S. D. Faircloth.


Carl

 

<strike>Wanted to pull the AAV today. I have the 90 deg. hose off, and thought it would pull right out. It won't budge.

Any hints on how to get the AAV out?</strike>


Never mind. Got it out.

 

Quick Update

Finally, got the re-cored radiator installed, and everything is running cool and collected. Car runs great, except for one issue.

I pulled the AAV and soaked it in carb cleaner for several days while I was waiting on the radiator. Tested and it fully opens and closes with temperature. Replaced the 90° hose when I reinstalled it.

Funny thing, my idle is still a little low, and numerous turns of the idle control bolt on the AAV have little to no effect.

What's up with that?

 

The AAV is still not working as it should, I think. Did you clean out the idle screw drillings and air passages? The air passages controlled by the screw may be a bit blocked. You could pull of the AAV again and direct compressed air through the idle drilling, you would need a long slightly bent at the end blowgun to do this. There are holes you can see in the plunger, looking down from the top of the AAV, these could be blocked with gunge.


Assuming when the car is cold the AAV is giving you enough revs (is it?), when the engine is hot and the AAV is closed, idle speed air goes down the intake tube on the side, then at 45 degrees downwards though the screw passage into the barrel of the AAV, then up though the holes in the plunger to the intake manifold. If the revs are Ok at AAV cold, but unresponsive to the adjuster at hot, then this passage is probably blocked somewhere.
Greg

 

maybe the heat has opened up an air leak or warped the butterfly position.

 

I did clean out the air passages, including using compressed air, and multiple soaks in carb cleaner, more compressed air, etc.


I think the idle is low overall.

It isn't really cold here yet, but starting the car first thing this morning, it idles at about 600rpm and warm idle is around 400rpm (assuming the tach is accurate).

 

The 600 rpm on a cold engine (regardless of the outside air temp) is low. From 7000 miles away, I would reckon your AAV is not opening properly. Grant Francis has a really good AAV fix, that involves removing the piston from the barrel and cleaning it all up so it slides nicely. I have recently done this for another reason, and Grant's method is really good. The nerve wracking part is taking the AAV apart, and this involves a saw cut to the ridge round the top of the barrel to release the pressure holding in the piston. This is his writeup.
AAV rebuild procedure.doc


To be 100% sure the AAV is the problem, you could remove the 90 degree pipe between the AAV top and the end of the intake manifold, cover about 75% of it with your hand, or a piece of softwood, and ask a friend to start the car. The engine should race before the injectors switch off at 1400 rpm. If so, then the AAV is certainly the problem.


Greg

 

Update on the low idle issue.

I confirmed that the AAV was acting as it should, but still had the low idle.

I took a look at the butterflies and I couldn't even get a 0.001" feeler gauge in there. I adjusted both to 0.002", and that made a huge difference. Now the idle adjustment bolt on the AAV actually adjusts the idle!

It also now idles more smoothly with less variability in rpm (though not perfect). I may go back and double check that the adjustment is perfectly at 0.0002" on both.

When I was in there adjusting the butterflies, I noticed that the walls behind them were fairly dirty. Should these be cleaned, and is there a way to do this without dismantling the linkage or more?

Thanks!