Hi all, I'm back! The Jag's been sitting in the garage all winter, and I've finally gotten around to going back out and doing stuff. Last weekend, finished reassembling all the stupid ignition wiring and dealing with the aftermarket security system, so now I can start her without having to jimmy the valet switch. Yay.

After double checking all fluids, charging the battery (which I'd disconnected over the winter), and all that, started her up. She started pretty easily, but I did notice a couple of things:

1. Idle was a bit rough at first. Not too terribly surprised or worried, since it had been several months since last start. But, something to keep an eye on.

2. More concerning, as I remember this symptom before she was put away, is that after starting, if I depress the throttle it will sputter and almost stall. If I release the throttle, it goes back to idling. It did this before, too, though not as noticeable. Once it warms up a bit (and it wasn't exactly "cold" here last weekend, mid 70s), idle smooths out and depressing the throttle doesn't cause the sputter/stall.

I'm thinking either there's a vacuum dealio somewhere (wouldn't surprise me, I haven't yet replaced all the vacuum lines), or possibly the TPS being flaky, but not sure if I'm missing something else obvious, or if this sounded familiar to anyone.

Thanks in advance for any suggestions!

1986 XJS V12 Coupe

 

The 'could be' list is a bit long but.....

Since the problem goes away once the engine warms up a bit my first thought is that your coolant temp sensor is on the fritz. This sensor commands the ECU to provide extra fueling...which you need with a cold or cold-ish engine.

The CTS can be checked with an ohm meter or, if you wanna take a stab at something, it is easily replaced (10 minutes) and isn't expensive ($20 or so). Not hateful, as guesses go.

Cheers
DD

 

Coolant sensor isn't a bad call actually. Time to grab the wiring diagram and the voltmeter. Or, might just see if I can find one and replace it if it's that cheap, and avoid the "iffy" part of it.

I did notice that the coolant light came on, too, but chalked that up to having sat for so long (and the thing needed topping off). I know that's a different sensor, so not related to the CTS.

 

Just a quick update. New CTS put in, and it did seem to help somewhat. However, when removing the old one, I see the PO managed to break the connector, and then "fix" it with some kind of rubber caulk gluing it into place. Sigh. So I'll need to get another connector at some point.

It still "chugs" a bit when depressing the pedal (or even manually twisting the throttle up top), but doesn't seem as bad, so time to check out the TPS.

(Oh, and other side note, stupid coolant light stays on now, so likely need to re-bleed the cooling system. Also noticed the crossover pipe cap appears to have sprung a leak once pressure builds up... but that's not related to the chugging. )