Random idle when hot

[800beast]

Hi guys, hopefully someone can help me out but I know it's hard without seeing the car in person. I took my hatch for a cruise on the weekend and when it was hot (not overheating) the car randomly decided it wouldn't idle and stalled coming up to the lights. We let it sit for a bit and then decided to head home and it ran fine pretty much the whole trip home. I've been having a look but can't seem to find anything obvious wrong.
On checking the secondary diaphragm I can suck down the tube and the diaphragm pulls in a little but quickly returns and doesn't hold vacuum, is it stuffed? Could it be letting air past the carby into manifold.
I should add it's a f8b auto.
Thanks in advance.

[Brayden]

Two possible issues that I can think of:
1) Spark is breaking down due to heat - check leads and coil.
2) Dirt in the carby that is getting stuck in the jet and causing the engine to stall. (Not heat related).

[800beast]

Thanks Brayden,
The leads have been replaced recently but not the coil, how would I check the coil?

Also what number/heat range plugs do they take, could they be incorrect?

I will put a carby kit through it next week.

[Brayden]

I'm not sure if there's a specific way to test a coil, but if the stalling only happens when the engine is hot, and it refuses to start again until it cools down then the coil is probably the cause.

If the problem is the carby then it will usually splutter and stall, but start again and run like a busted arse until the dirt circulates in the float bowl.

Correct plugs are BPR5ES from memory, but the book at any auto shop will confirm.

[Tez]

The other ideas are equally valid, but have you considered whether or not it is possibly the carby icing up ? - I had a similar issue once when on a cruise - extended driving at higher speeds causes the engine to warm up to running temp, but the carby gets cold, and when you come to a stop, the thing splutters - feels like it's 'constipated'! and then it stalls. Sit there for about three minutes, and the heat from the engine will warm the carby back up enough for it to start again. Damnedest thing until you realise what is going on. Do you have the 'hot air' bypass tube from the exhaust manifold to the carby inlet fitted and switched in? - I fitted one up to mine (was absent when I got the car from QLD) set the air intake to 'winter' in the cooler months and it's never done it since.

[800beast]

I doubt it's icing up, inlet air temp isn't very low and I have a open filter so it gets some warm air from the engine bay.
I changed the coil and took it for another decent drive, the idle was around 600 rpm which is low but it drops below 500 and stalls when hot. I have adjusted it to around 900 when in drive but it gets hot and then the idle sort of pulses up and down but doesn't stall now. Might just need a carby rebuild.

[800beast]

hadnt driven the old girl for a while but took it out recently and finally it played up when i just got it back in the shed. it appears the primary jet is dripping fuel into the throat/venturi and causing it to surge and stall from getting too much fuel at idle.
looks like i will have to put that carby rebuild kit in it after all. The only real reason im holding off is the having to tune it afterwards.

Also, is there a simple way of stopping the EGR valve from operating. my pipe that runs from exhaust to intake is a bit rusted and wont come off.

[Brayden]

Odds are pretty good that the EGR already stopped working a long time ago. If you want to be sure it doesn't open then disconnect and plug the vacuum line on the manifold pot.