Hello, I could use some help getting my XJ6 back to running properly. Since I bought it in June it’s run a bit rough, but lately it’s gotten worse. Here’s the history: It was originally just a rough idle, it would occasionally bog down to a low enough rpm at stop lights to knock the AFM on the wheel well which was annoying. Then it gained another issue, when it was warm, if I left it sitting a while, it would do a start/stall. It would immediately start, but stall out within a second of letting off the key, unless the pedal was held down a bit. Once you could get it running for a few seconds, it ran and idled as usual. Then one day it stalled while going down the road, and then kicked back on. This got my attention and started efforts to fix it. I adjusted the idle up to about 900, and jumpered the coolant temp sensor socket. That seemed to make it run better (when warm, when cold it obviously did not like the jumper). So I replaced the coolant temp sensor, and for a couple days that seemed to fix it, but alas no. When I start it on a cold morning it runs atrociously. I can be going down the road, not moving my foot on the pedal at all, and feel it bog down, running very rough, then righten out smooth out and accelerate a bit, bog back down, etc. Once it’s warmed up, it runs fine. In addition, the start/stall issue is back. I would love any suggestions as to whats wrong! Thank you.
The ‘could be’ list might get long and you might well have a stack-up of different faults.
There are any number of jumping-off points but I’d begin with:
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Check the ducting between the Air Flow meter and the throttle body. Properly in place, tight, not split?
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Carefully examine wiring and wiring connectors at the firewall relays, injectors, water rail sensors, ignition coil, ignition module, and injector ballast pack . Connectors clean and tight? No frayed wires? Also check the bundle of ground wires at the rear of the water rail.
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Remove the under-dash trim panel and, with the engine running, gently jiggle the wires at the ignition switch. Any response from the engine?
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Run a jumper wire from the battery “+” post to the coil “+” post and drive the car. Any change?
Post back. This is just round one 
Cheers
DD
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Adding to Doug’s sage list, Jake; verify that the AAV is half open when cold, and fully closed when hot…
You don’t positively state if the engine is running smooth when hot - nor eventual idle rpms differences hot and cold. Cold idle should be 200 - 400 rpms higher than set hot idle - done by the cold open AAV. Enhanced cold idle is very important for cold starting and idling during warm-up.
Doug’s advise on jumping coil to battery is very pertinent - that the engine sometimes quit implies loss of ignition - which also noticed by the tach dropping to zero with the engine still turning…
Frank
xj6 85 Sov Europe (UK/NZ)
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Thank you Doug, and Frank!
I’ll start working through the suggestions and report back when I’ve done them all throughly. May be a couple days. Frank, I’m familiar with where. The AAV is and what it’s for, but I’m not sure how to verify that it’s halfway open (as opposed to all the way). How would I go about that?
Thanks again,
Jake
Jake, does that help?
David
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With the engine cold; remove the top air hose and peer inside, Jake…
…the air passage should be about half open, more ore less. With the engine hot; the slide is moved to close the air passage completely. The slide is moved by a bimetallic spring reacting as it heats up, and the slide tend to stick in accumulated gunk over time. It can sometimes be freed by forcing the slide with a small screw driver. And applying some solvent may help…
But the first step is to verify that it opens and closes with temperature - if not; we can get into further remedial actions. A point here is that the idle must be set with the engine fully warmed up, and the AAV closed - or issues may arise…
Frank
xj6 85 Sov Europe (UK/NZ)
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Hello all, don’t want you to think I’ve ignored the suggestions. Since the day you all made your suggestions the car has not acted up once, other than a slightly rough idle. None of the more exaggerated symptoms have appeared, making it difficult to determine which suggestion makes any impact. I did try the jumpering of the coil, the car seemed to run pretty much the same, it felt like it maybe accelerated a bit faster. I was surprised when I turned off the key and it continued running! I figured even with direct power to the coil the rest of the ignition system was likely powered through the key, but I suppose not. Beyond that I’ve done no further testing because I haven’t had any symptoms to test their effectiveness on. If it adds anything to the diagnosis, it’s improved operating condition corresponds to the arrival of colder weather, but not directly. The first day it was below 60 it ran abysmally on the warm-up, as I initially mentioned. The second day, and all since, it’s been running fine.
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The battery to coil pos backfeeds power to all engine management systems from the battery through the ign key connections, Jake…
…the jump should only be used as a test, or as a deliberate bypass for a defective ign key connections - not permanently connected. And the jump has no effect on engine running…
Frank
xj6 85 Sov Europe (UK/NZ)
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