Unpredictable throttle?

[john853]

I am really enjoying the new-to-me 2008 XK Convertible that I bought just before lock-down, now that I am not under house arrest and am allowed to drive to places.

I am slowly getting to know it's quirks, and find most of them entirely forgivable. However, there is one that I would seek advice on, and the dealer says they are allowed no access to anything that could improve it.

I think what is going on is this; but I would welcome your knowledgeable opinions please. I think it has some adaptive throttle software that detects how you drive and adjusts the sensitivity of the throttle action to suit your style; is that right?

Maybe I am a bit too Jekyll and Hyde for the programmers? When out driving on empty, twisty country roads (which have been available in Dorset in the aftermath of lock-down) I drive briskly and enjoy employing the skills of driving a front-engined, rear wheel drive car of impeccable performance. After all, I grew up driving an MGA in the days before they invented Motorways (or, it has to be admitted, traction control, ABS, active suspension or dynamic stability control). Then I come into town, and become a courteous old gentleman who does not want to compete in the traffic-light drag-race with the young tear-aways with big bore silencers to match their big-bore heads. But I find that sometimes the car wants to compete even though it's driver does not, and we take off like a rocket for 6 ft until I can restrain the roaring beast. Then other times, it takes off exactly as it's driver wishes, with brisk progression to a safe speed. I don't wish to dawdle, but I do wish to feel in control and to be the one who decides how much acceleration we use.

I think I blame the programmers! But am I right, does anyone else notice this, and is there anything I can do about it? I have tried resetting the throttle sensor by steadily moving the throttle pedal from right up and then right down to kick-down twice, with the ignition on but the engine stopped. That possibly works for a while, but I don't wish to have to do it every time I see a 30 speed limit sign!

[J44EAG]

Throttle body potentiometers fail occasionally. It could well be that you have one that is past its prime.

The potentiometer is set at the factory and paint is applied around screws on the unit to denote correct positioning of the pot relative to the throttle body. In normal use, there should be no need in service to adjust its positioning.

A similar pot exists on the throttle pedal unit which again may be showing signs of breakdown.

Also worth investigation is breather sludge fouling of the throttle plate within the throttle body together with ratchet action of the throttle plate due to that fouling. A good clean up of the throttle body throat above and below the throttle plate may reduce the driver effort needed on pull away. You may just have a sticking throttle.

Mike K