Have finally changed the engine in my Felicia fun but stalls when cold when warmed up runs fine well about 800/900 rpm but when the heater is turned on wether cold or hot air the revs go mad up and down between 200-900 rpm any idea what it could be

Not much information to chew on. Unless you let us know everything you know about the engine swap, we can only shoot in the dark. You have full access to your car and we are not wizards. Any possible mistakes you did on wiring? What is YOUR guess on the issue? Give us more clues.

It had stalling problems before the engine swap engine was swapped because was letting out blue smoke. Did have throttle body clean and reset but no different all parts that were on pickup before are the same leads. In did notice that thermostat was not working properly blowing Luke warm so I swapped just the thermostat over to which I now have hot air coming out temp gauge goes just over half way. I did notice that the temp sensor on pickup had a blue ring of plastic while the one on the other engine had a yellow if that makes sense. Without the heaters on it revs fine no eratic idle untill they are turned on full

The blue ring on CTS means "for cars with air conditioning".

By "the heaters on full" I presume you mean the fresh air blower on highest speed. The only thing that happens then is a big current draw that a good battery and alternator should easily put up with. Here are a few questions for you:

1. if there are other high electrical loads turned on (high beam + radiator fan) will the idle go wild?
2. what is the DC voltage on battery when the blower is on full?
3. what is the DC voltage between B terminal of the alternator (big nut) and car chassis with blower on?
4. did you check all earth points for corrosion?
5. did you check for corrosion on all engine related connectors and computer?

Edited 4 May, 201610 yr by RicardoM

i havent got any way of checking voltage apparently some parts where changed over becuase they didnt look to good. At the moment this is not as important as on my way home in it tonight the temp just touched red so turned engine of and rolled to the inlaws. Coolant had all gone even though topped up the day before but near the thermostat housing there was steam appearing can not say directly where it was coming but when i put in new fluid it was wet under the thermostat housing and the bottom right corner of the engine checked all pipes and no splits. all pipes were in great condition could one of slipped a little.do i buy a  new thermostat housing just wonder how would you guys go about it where to start if a pipe has slipped best way to check anything to put on pipes and look for it bubbling 

You should be able to buy a multimeter for about £12. Mine saved me a garage callout fee about a week after I bought it.

 

Water leaks usually leave a white, green-blue, red-orange, purple ( those last 3 dependant on type/colour of anti-freeze used) or rust coloured residue near the leak point.

After such overheating event, the 'pipes' or the thermostat might be your last worries...

wow, red line's bad for the poor felicia, i have blown my headgasket like that. if you didnt see any leaks and just steaming, i would say your engine is burning coolant, mine did that, she drunk all the coolant and overheated to redline, i had to replace cylinder head also because it had pieces of metal blown from it..

It sounds like maybe the temp sender you fitted maybe wasn't fully seated in the housing and has let the coolant out past the O ring

I wouldn't worry too much about the 1.6 engine it will take a fair cooking due the steel headgasket.

Idle could be faulty throttle body or an air leak on the manifold etc.