Loss of power

I opened a new topic last evening but I have been unable to find it on the new forum site so I am repeating the question in case I failed somewhere along the chain
I drove my 2008 Jimny 10 miles to the office yesterday and 40mph on level ground was the best I could manage.  On the return journey it appeared normal for a couple of miles and the last even more power.  It was like a modern car in limp mode.

It passed its MOT recently but was told it needed new plugs and coil packs whatever they are.  The engine did not seem to misfire or sound rough so I have no leads.

If anyone has any idea I will be most grateful for any pointers as to where to start looking for the problem.
Stalker

First off when was it last serviced?

Second while it's entirely reasonable that plug and coils would help it's more likely that the front catalytic converter in the exhaust has decided to disintegrate and the debris is blocking the second catalytic converter further back in the exhaust, this is usually what happens. If you tap the exhaust when cold and it sounds to rattle, that's one indicator, otherwise it will need splitting between the cats to see if there is obviously debris in there.

New plugs and coils are cheap enough and easy for a newby home mechanic with a basic socket set. The exhaust system however is both expensive and a minefield of broken bolts for a novice.

Thank you Lambert for your advice, a necessity for passing the MOT was a new cat so hopefully that possibility was covered.

Do you know if I can source coils through Martin?

Me again, I have just looked up ignition coils on the internet and they all appear physically the same but some are £15 each and some from a main dealer are £160 each. How does a novice ever decide, perhaps Martin is the best person to ask but interestingly some of the less expensive coils offer a 5 year or 50,000 mile guarantee.

I've used both the cheaper ones and proper ones and the cheaper ones are often a source of their own problems like misfire. I'd get hold of Martin and see what he can do.

Also, just for clarification when it wouldn't go over 40 was that as a result of the engine not reving fast enough ot was the engine at full revs in top gear and that was as fast as the car would go?