Engine stalls when decelerating for lights etc.

[jimthack180]

My 1993 XJ40 4.0 ltr Sovereign is excellent in all respects apart from this annoying trait. When approaching a junction, or traffic lights, under gentle braking, the engine will just die. This can sometimes be very embarrassing, but on switching off, then on, she always starts again straight away. No fault codes come up, and the fault is unpredictable. For example, it happened 3 times on the same day in late December, then not at all on a trip to Ireland of over a thousand miles, then it happened twice last Sunday in Norwich, but not since. Anyone else experienced this?

[andypryce]

Hi,

Had exact same on my 91 XJ40 and it was the throttle body, needed a good clean out, was fine after that.

andyp

[J44EAG]

Yip, me to on my V8 S-type.

My article early 2011 in our magazine describes in minor detail a clean out operation prior to fitting a second hand unit due to TAC module failure.

The original unit was filthy at 44k miles. A clean out with throttle body/carb cleaner, soft rag and a very soft tooth brush really did help. Faster idle as less grunge around the throttle plate and a faster return to shut action to idle position as a result of the clean up. Rubber gloves suggested to avoid cleaner absorption through human skin and also to keep the vile black grunge from staining the skin.

Go easy on the throttle body throat. Many have a special coating to help reduce grunge build up. Apparently that needs to be left intact.

Mike

[jimthack180]

Thanks guys. I've had a look at the throttle body and it was a bit gungy, so I've cleaned it out. I also found a lot of milky gunge in the breather pipe from the rocker cover to the throttle body intake, so cleaned all that out too. Unfortunately, I've still got the stalling problem, although the engine does idle much smoother than before.

[andypryce]

Oh dear, not sure where next, hopefully someone else will know...

andyp

[J44EAG]

I expect Rob will be along shortly and will have seen this issue before.

I`ve had a similar issue in the past which turned out to be a duff temperature sender in the cylinder head. Simple as that. Worth checking for corrosion if nothing else.

I`d be looking at bringing in first principles here as my own knowledge is cloudy on XJ40`s. It is ages since I last spannered one.

Vac advance leaks, idle speed valve sluggishness, throttle pot, ignition timing, correct throttle plate angle, various pipes checked for integrity, maf sensor cleanliness, airflow meter moving easily, NRV on brake servo, fuel pressure reg, crank sensor etc. These ideas model non specific but never the less worth investigating. Just a few ideas here until someone more informed can give you a better lead.

Mike

[robv12]

may be worth having a look at the kickdown cable and setting the adjustment correctly

or tweak the slow running slightly