Temp gauge reading hot when engine cold and erratic throttle

Hi all, just booked my 1.3 efi porter in for it's mot and when i got home the misses told me the throttle was revving up and down in traffic and then returns to normal, then starts again a few miles later. I popped out to check it, started it and noticed the temp gauge reading all the way to the hot (normally only sits in the middle), so i put the heater on full to cool it down and it blew cold air out the screen vents I asked the wife and she said she had been home for hours so the van was stone cold. So i thought it could be a faulty temp sensor but could this be causing the erratic reving, if it's sending false info to the ecu ?? Any help as I'm completely stumped.

They hunt like that if the fast idle valve is open.

The fast idle valve stays open if there is no coolant in it.

And three guesses why there is no coolant in it!

Good luck

I can try and bleed the air out of the systems but it gets changed every 2 years and filled back up again by the approved method and no problems what so ever up until now. That whats made me think it could be a faulty temp sensor telling the ecu to alter the engine rpm? Was only a thought i will see if i can get the temp sensor off the rad pipe, its a bugger as it's just above the front diff so no access from below, unless it's not in the rad pipe and on the block somewhere?

That isn't the temperature sensor in the pipe. Thats the fan switch.

I've been trying to find a coolant temperature sensor for my Hijet, if yours is the same type I hope you have better luck than me in finding a new one.

no it appears to be low on coolant i topped it up following the destructions behind the front grill and all is well again. phew!

Ask yourself where did the coolant go.

I'm a little worried as i can't see any obvious leaks under the car, but it's been raining a lot lately so not always obvious. I'll be keeping a close eye on the oil for milkiness in case of head gasket failure, but I've had one go in the past where the water way leaked into a piston so the oil was fine but loads of water out the exhaust. Watch this space

You don't get oil/water contamination on most modern engines since like the 1980's.

Its one of those things I hear everyday, and I just want them to stop repeating it, keeping the myth alive.