i don't know if same symptoms but just "kinda" sounded like it

and that should have been fuel rail/injectors .. not inlet

Yeah I get what you mean and thank you. I will have a geezer at both once I get some more time .

Pulled the camshaft out and even after 350,000km, it looks clean under the rocker! Okay I cheat, the engine probably had only done 180,000km since I did the head.

Well an update.

Replaced the cam with the stock XR6 cam and put everything back together after a few dramas. Car started first go, went for a drive around the block and everything was okay.

Will try again tomorrow and the day after, however the car has been sitting in the garage, so not as cold.

This issue has only been going on since the cold weather, so it could definitely be temp related.

What data input does the ECU need to start the car? Temp/Smartlock/etc? Would be good to know if any of the sensors could playing havoc with the start up. By trying 3 different ECUs, it obviously isn't the ECU and after a few attempts of starting by swapping out ECUs, the car would have warmed up a little with each kick so would run fine. Could a loose exhaust manifold cause starting issues?

What sought of measuring equipment do yo own, eg fuel pressure test kit, digital multimeter, scope or scope meter.

Only multimeter unfortunately. I could possibly get my hands on a few other items.

Did you leave ignition on for approx 30 min after swapping ecu or does replacement have j3 chip as well .
is smartlock light going out .
does interior light work
Possible ecu relay
Can you hear fuel pump when key switched on

Sorry didn't get back to you and thank you.

1) After ECU swap, I did not leave the ignition on for 30 mins. All ECU replacements have no J3 chip.
2) Smartlock light goes off as I put the key in and start the car. Car starts and idles, so that would mean not Smartlock? Could Smartlock module kick in AFTER car starts and shuts ignition/injectors?
3) Interior lights work, I thought it may be the issue as I had an LED interior light, but the car still worked with the LED light. Swapped it back with the normal and no fix.
4) Had a look at the ECU relay, looked fine and cleaned up the connectors just in case. No fix, need to find a spare one I can borrow to try.
5) Fuel pump primes and car idles fine for 30 secs before dropping. I connected 12V directly to pump to pump fuel out of the car (full tank of 98) through the new fuel filter and into a jerry can. Worked fine, but honestly don't know how fast the flow should be. It took about 2 or 3 minutes to fill a 5L jerry can, from those figures, that's around 100-150L/hr, does that sound right?

I drove the car around the block a few times and it starts and idles fine. Someone wanted to have a look at it, so met up with them at the local shops, car started and drove fine. Got home and it stalled on me going into my driveway. Tried to start it up immediately but it would not fire, just turning over. Left it sitting for a minute and tried again, it just turns over but does not catch. Left it again for a bit, started it with a bit of throttle and it started up, hesitantly. Reversed back out to park on the street only for it to just die. Started it up again with throttle input and it started and drove forward to finish parking. Idle hangs around 2500RPM and I was watching it slowly drop only to see it drop quickly, pick up a little and drop again and completely die. I turned it on again and the same thing.

So the RPM would get up to 2500RPM and hang, drop slowly but smoothly to 2300, then a quick drop from 2300-2100, then smooth drop to 1800, quick drop to 1400, smooth to 1200 and then just completely die. It's like it's dropping cylinders as it lowers down to idle. I repeated this a few times and the quick drops happen at random RPM. When I rev it up, it seems to be okay as soon as I let go of the throttle it just goes to s**t.

Completely at wits end here. Don't plan on spending anymore money, but have a few spare parts I can use to swap over to see how things go. I will pull the injectors out, fuel rail and fuel pressure regulator to have a look if it's dirty. Pull the fuel filter out again to see if it's blocked and maybe check the fuel pump pick up...could be blocked?

Not sure if the distributor I bought (brand new, aftermarket) could be an issue as well. I know it's new, but have heard things can go sour with these aftermarket units.

Can't sell the car as a whole as it doesn't even run properly...what a nuisance.

There can't be much wrong with it, in the previous post when you put it back together it ran alright. Has any of the wiring been modified, when you say it was revving at 2500rpm did you have he throttle open or was it doing it on it's own,

Sorry haven't had a chance to look at the car until 2 days ago.

No modifications to wiring, all stock. Only wiring is for neutral switch and auto temp trick as it is a manual conversion, not sure how this would affect the engine cut out.

The rev hang is without throttle input. So car would die and won't start again until I turn the key to off. Turn the car back on and it would start straight away but reving to 2500RPM. Slowly drop from there smoothly and abruptly as mentioned before.

So this is what I did 2 days ago:

1) Cold start fine, drove out to park on the road, idled for 5 minutes and cut out.
2) Start car again, rev hangs at 2500RPM slowly dropping to idle and held for a few minutes before cutting out (smooth drop, not abrupt like previously)
3) Unplugged ISC, tried to start car and it wouldn't start.
4) Plugged ISC again, started car, car idles for a few minutes and cuts out again.
5) Started car and left it to idle, unplugged ISC and car dropped revs a little but continued to idle.
6) Car still idling after a few minutes, I plugged the ISC back in and car dies.
7) Start car with ISC plugged and left to idle, but idle is a little rougher and cuts out after a few minutes. Car is now warmer but the needle is at the first marker.
8) Replaced ISC with another I have (from old engine...not sure if any good), car started but died seconds later.
9) Started again, car starts and dies immediately, so old ISC is stuffed I think.
10) Put original ISC back in, starts, idles and dies again after a few minutes.
11) Start again (starter motor getting a work out), left to idle, unplugged ISC and car idled for 10-15mins while I gave the car a quick wash.

Now at this point I am pointing my finger at the ISC or the Throttle body or both. I cleaned the ISC with some carby cleaner, put it back in but nothing. As the car was getting hotter, the car cutting out happens faster. I left the car sitting for about 30 minutes before I drove it back into the driveway. From kerb to reversing into driveway took 8 restarts...in each case, holding the accelerator down did not help keep the engine going, it would still cut out.

I have a spare throttle body, but the ISC bolt hole in it has been stripped. Is it hard to swap the throttle body sensor over?

Also, how do I check if the ISC is doing its job? It helps me start the car, but not idle, instead unplugging made the idle work fine for a while. Did not try to drive with the ISC unplugged because it would still cut out at some point, something I should have tried though. Once at operating temp, the cutting happens faster, so I am now not sure if it's the ISC/Throttle body.

This thing has me scratching my head!

Left the car to sit for too long the battery died completely and had to recharge over 3 days using maintenance mode. While I was waiting for that I pulled the throttle body and ISC out and gave them a good clean. They were filthy. Put everything back in with a well restored battery and the car started first go without issue. Car idles but when the throttle was opened the car would just rev hang at 1300RPM and sat there for a while. I unplugged the ISC and the revs dropped and immediately plugged the ISC in again and it idled normal. Left it to idle for 30mins without issue getting the car to operating temp. This is all without intake connected. Turned the car off and left to sit and then eventually put the intake back on. Turned car on and left to idle with ISC connected for a few minutes. Gave the car a rev and no rev hang. Drove the car for about 5mins and everything was working as it should with no rev hang.

For now it seems good but will need to drive it a few times to make sure the issue is fixed.