Cutting out when coasting

You get fuel cut above a certain RPM when decelerating with the throttle closed but its usually not noticeable.

It is, but it is what you expect- you have a dead engine holding you back. The braking comes from pumping losses, and with a shut throttle you don't get much air in there. If the throttle is wide open, and the engine stops firing there is a lot more effect as the cylinders get to compress a lot more air.

Donkeys ago I had a missfire at idle on my EFI rangerover (was the ignition module in the end). Either I read in the fault finding guide, or someone suggested, it might be the vacuum switch on the manifold, so I shorted it out, all the engine braking disappeared- took two feet on the pedal to stop the thing from 40- you wouldn't have thought an auto had so much engine braking without lockup :ohmy .

The point of my rambling is if the throttle is closed, or the ecu thinks the throttle is closed, the fuel will cut off.

If the throttle is slightly open then more air gets to the engine and there will be slightly more braking effect.

I'd look at the throttle position sensor output, and see where it is with the pedal released, and what happens as the pedal is pressed gently.

The sensor may be faulty, or out of adjustment. (Or there is too much slack in the cable, but I dare say you'd notice that)

facade wrote: The point of my rambling is if the throttle is closed, or the ecu thinks the throttle is closed, the fuel will cut off.

Only while it is still above 2000RPM so it shouldn't 'cut to tick over'. Unfortunately OBD2 doesn't allow Idle Position and injector pulse width PIDs so you need an OBD1 capable tool to test this while driving. The FSM recommends the use of a stethoscope to test this while stationary if you don't have a tool.

Thanks for all the input, much appreciated!

While I was fiddling with the oil pump seal a few weeks back, I noticed the throttle cable had a little more play than I'd like so I just tweaked it without thinking, ive not experianced the issue since but that's not to say it's solved as I say it seems to be only certain scenarios that bring it up.

Rhinoman, what's the deal with 2000rpm? Perhaps there's something in that, maybe when I'm trying to replicate the issue im not above 2000rpm, I'll give it a go on my way home but I need to go easy (ive a hole in my radiator )

I've only got an OBDII tool, it fits but it doesn't seem to connect but it can be a bit random sometimes.

2000RPM is fairly normal, you have to decelerate from over 3000RPM for fuel cut to occur and then it cuts back in at 2000RPM, that's probably when the ISC cuts in to give a 'dashpot effect'. What year is your Jimny? the OBD2 models need the Suzuki SDT tool to access the OBD1 interface, earlier models need a Tech2 or an SDL interface. They all use the same connector which is a standard diagnostics connector rather than an 'OBD2' connector as it often erroneously referred to.