P38A 1997 4.6 V8 Erratic start up & coolant loss

Hi,
I've been cleaning up my P38 possibly to sell. It has been using coolant lately but the temperature is firmly at 12 o'clock. Engine has 121,000 miles, FSH.
I decided to get the engine and engine bay cleaned up. (I appreciate this has it's risks but I took it to a place that does this all the time - on all types of cars)
After the clean up the engine started first time as normal, then the revs climbed to 2000 rpm and stayed there. Started it a couple of more times, same thing. Then on the 4th attempt the engine started up, climbed to 1500 rpm then settled down to a normal idle. Ran it for 10 miles.
Went to the supermarket, when I came out the engine started erratically (almost like an old car would do if you pulled the choke on on a warm engine) then wouldn't idle.
With a bit of the throttle the engine seemed to clear itself and ran normally.

A few questions if you please: Is this an issue with the cleaning (i.e. has something been damaged) or is it a larger head gasket issue or the old slipping liner story? (One that just happens to have shown itself at the same time)

Thanks in advance of any replies, Alan

Might have to get the codes read to be sure...

I would suggest it's likely to do with the clean. I wonder if something has come dislodged?

Blasting water in to the engine bay does have its disadvantages..

As for coolant loss, it could be several things.

1) the heater core O rings, when mine failed it would lose a litre of coolant per week.
2) Valley Gasket.
3) Radiator.
4) Front cover gasket
If it has dropped a liner, a clack clack noise is a dead giveaway and either coolant in the sump or finding its way it to the cylinders, which is very evident.

Most likely a leak of some kind.

I'd possibly reset the adaptive settings and let the engine relearn... mine rev'd high after a clean out of IACV/ MAF - reset settings, and all back to normal. PM me, I'm v close, I cd bring Nano, but not til next weekend...

In case it was the cleaning, get a can of contact cleaner and clean out all the electrical connectors. Also check the state of the plug leads both at the coils & spark plug end.

Could also just be the coolant loss is getting worse, and you have head gasket or other engine issues.

I have Nanocom for GEMS in Langley just of J5 on M4. Could do the diags & reset on evening if you want. PM me.

I have had various leaks over the years and would think it is most likely the rings in the heater. Also dont trust the temp gauge on these it will sit at 12 o'clock but be quite a way off in real temp. Have a look at the cap on the rad they are often faulty.
Check that the cables to the coil packs aren't loose or damp they can give you some fun Hope that helps