Intermittent loss of power ?

My 2006 JimnyVVT is experiencing a loss of power every third or fourth longer journey.....travelling at around 65 or 75 mph it suddenly loses power which shaves upto 20mph off the speed then evens out. At this time it is noticibly rougher (though nothing like as if it were misfiring or dropping onto 3 cylinders...it feels almost like there is some kind of resistance holding it back). After 5 to 20 seconds or a little longer it recovers and normal power is resumed ( having dropped from 5th to 4th to compensate for the loss of speed).

I've had it on a diagnostic at my local garage and the only fault found was with the throttle valve which he took out and lubricated..but the problem has continued. Nothing else was flagged as a fault despite my expecting a coil pack problem. In all other respects it idles smoothly and evenly, and continues to work perfectly throughout the rev range.

Has anyone else had this problem? Is it likely to still be the throttle valve or something else?

Thanks.

Hi, could be a blocked cat, when it loses power check if the usual amount of gas is coming out of the tailpipe using your hand

Could be crankshaft sensor starting to play up. If it is it will get worse to the point that it cuts out when hot.
It doesn't set a fault code.

Thanks all.

Might replace crankshaft sensor as it seems to be a common problem and an easyish cheapish fix at this stage. At least it'd rule that out.

Coil packs .... That's how mine started. Got some NGK replacements of the bay. Has been ok all year then started hanging back a bit then cleared , very intermittent.
Took exhaust manifold off to find the cat had started to collapse (2 cats on a VVT) so just knocked it out. Been fine ever since and no effect emissions wise

I've yet to sort this out ...I've been waiting to see if it gets worse or the problem becomes permanent.

So far, suggestions are...blocked fuel filter, blocked cat (s), coil packs, crankshaft sensor, camshaft sensor, spark plugs/leads, throttle valve, oxygen sensor (lambda).

All a bit confusing, but I'd have hoped some of these might show up as a fault on a diagnostic?
My gut feeling is an ignition problem but that doesn't rule much out from the above list

Skywalker: If I read your reply correctly, your experience is that the coil packs initially failed, all was then ok for a while until later when your cats collapsed.