Question: About cleaning of the throttle potentiometer of XJS 4.0

Hello,

I doubt that the cause of the stall at my XJS 4.0 (1996) would come from the dirtiness of the throttle potentiometer because of the following comment in the service manual for XJS 4.0: The fuel cut off function is controlled by the throttle pontentiometer, and the conditions under which it occurs are progrmmmed into the ECU memory. So I intend to clean it up. Must I dismantle it for this purpose instead of spraying some carburetor cleaner to it?

Kind regards

You can do it either way

There is plenty of good info on the XJ40 list about the TPS and the 4.0 engine.
Do a search on “TPS cleaning” on that list you will see lots of other posts and pictures.

For example:

The XJ40 is a great place to get info on the 6 cylinder engines, there seems to be a lot more of them than in the XJS.

Ignore that. The XJ40 does not use the same potentiometer as the 96 XJS/x300. You have a simple 3-pin, outrageously expensive part, that seems to bench test well, but cause problems when driving.

There is no way to clean the TPS you have. It is completely sealed with no reason to drill holes into it.

The TPS has been know you cause all sorts of random issues, stalling out the engine certainly being one of them. Replacement is the best prescription for this 26+ year old part.

If you provide more detail on the stall, perhaps we can help suggest other common faults to look into, such as the crankshaft position sensor, another common part that can cause the engine to stall….or the EGR, or a vacuum leak…

I would certainly start at removing that throttle body and cleaning it out. If that hasn’t been done, the butterfly will be gummed up wreaking havoc on what that TPS is trying to do. It’s simple to do, not terribly time consuming, and should cost you less than a can of carb cleaner and a rag.

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I’ve cleaned AJ6 TPS in the past. The only outcome was that I realised it has a nice, red enclosure and is well sealed. If you have one as per photo below - leave it undisturbed, look for issues elsewhere - haven’t heard about any problems related to it…