998 efi problems

hi all new to site :-)
i have been working on my next doors hijet for ages now trying to sort out running problems
first of all was cutting out all the time then it would not start for while then it would restart cut out when you tried to rev it would just die
i changed fuel tank/pump loads of other sensors ect as we had a doner van later found someone had welded the lambda sensor in so got it out re-tapped thread and fitted new one and seemed to pick up then e/m light came on did blink code test which threw up code 42 coolant sensor fitted new one light went off and ran fine for about a day
now it keeps idling high and running high temperatures
any suggestions where i can start looking for faults light still on every so often with same blink code 42
any help would be great  
adam

Are you changing the correct coolant sensor, as I think those have 2 in the cylinder head. One that does the dash gauge, and another that does the ECU.

Idling high and running high temperatures could be the same problem:-

If the coolant system is not 100%, then the idle control valve does not get a good water feed, so it makes the idle high.

hi i changed one at the back single wire to it accessed from removing the panel in the back where would i find the other sensor many thanks

I think the single wire one does the gauge,

And the two wire one does the ECU, which is on the back of the head near the one you have changed.

will check in the morning sounds very promising will let you know how i get on

The single wire is dash only the real one is brass and you need a proper offset 19mm ring spanner or the dizzy bevel casing off it is about 4" above the exhaust level and slightly towards drivers side and changing it is what you need ours was a bastard after I broke it till I fitted a new one.

hi managed to sort running probs out was the two wire sensor how do i now clear all engine code faults from ecu many thanks

Disconnect the battery for a bit, leave it over night if you don't want to mess about.

Normally the warning light will go out if you fix the error, but it remembers the blink codes unless you battery disconnect trick it.

many thanks light gone out will leave batt off over night :-) thanks for help

I clear the code by only taking the terminal off standing up and then bending back over to refit it takes a few seconds.

thats a good bit of info for the 993cc