Running very rough - is a sensor the culprit?

Hi all, a quick synopsis:

Jimny runs rough from cold. Almost feels like it's firing on 3. Struggles to accelerate at all. Sometimes (1 in 10) once it's hot it's OK. Then the symptoms come back after stopping and cooling down.

There is nothing in the fault log
No EML light
Plugs and leads/dis pack are all good
Has had a full service inc new air filter etc
New exhaust inc cat
New tank of fuel (x 3)

So, we're guessing it's a sensor somewhere. But with no errors or faults shown, it's difficult to know where to start.

Has anyone out there had similar problems and solved it or can you give me a good place to start? We don't want to start buying sensors on the off-chance as they're not cheap!

Thanks for any help you can give.

Another possibility is a broken cam lobe, which happened to me about 4 years ago. However, :blush: I like the new lumpy sound and put up with it for a couple of years before replace the camshaft. On mine, it was the cabin end inlet lobe that chipped off, didn't really lose any power or economy, it was just a niggly thing but the sound made up for it :whistle:

That's something else to consider then.

The problem is, when it runs so badly, it's dangerous to drive. Pulling onto a main road it takes a good 30 seconds or more to even reach 50!

If it runs rough, but isn't detecting any faults, then it is either the crank sensor (rarely throws up a fault, it should as there is a cam sensor to check against) or something else it cannot detect, like a sticking valve, blocked injector, low fuel pressure, IAT sensor, Engine temp sensor or MAP sensor.

Can you read live sensor data via the OBD port and see if the IAT, MAP and engine temp are reasonable?

Thanks facade.

Will see if we can borrow a reader. The garage will do it but charge for the time. It may be worth an investment.

I see yours is a 2003. Is it a hard top? Have you checked for leaking hoses? Also the pcv valve at the rocker cover? Have you tried someone elses leads or coils?