Engine idle fluctuates high and normal and the engine light comes on.

o2 sencer

No such thing as a tune-up

All you did was replace spark plugs which should be
done every 3 years

Oxygen Sensors get replaced at 100,000 miles which you
also did

You most likely have an intake gasket leak,smoke test
the entire Evap System & Engine

You also are have bad igniton coils

You need to have OBII scan performed. The fluctuating idle sinus like a MAF sensor, Temp & fan are separate issues. Get scan done, that should identify exact issues.

The oil pressure guage will fluctuate with engine RPM. At idle it should be approximately 20 lbs./sq.in, at high revs about 50-60 lbs./sq.in. Hope this helps any concerns you may have. Good luck!

this is absolutely normal with a well maintained broken in engine. the engine is at rest when stopped,so the ecm lowers idle till you drive,which puts the engine under load.if it causes the engine to stumble or die,then replace air filter and set up the idle.

The harmoic balancer is located on the end of the crankshaft. This shaft is the largest shft in the engine and should be the one where all belts eventually run thru/over it. Check it out, let me know.
1ledsled1@comcast.net

Fluctuating an high RPMs sounds like a leaking or missing vaccume hose to me, I had simmilar problem found open hole with hose off, replaced it now the RPMs are under 1000 again.
As for the stalling I also am having a simmilar problem, and am finding air in the fuel rail, I suspect the fuel pump is going.
I cant go more than a mile without problems.

The check gauges light is normal because at 400 rpm it isn't running fast enough to build sufficient oil pressure. I am guessing maybe a vaccum leak???

Cars are SUPPOSE to idle higher when the A/C is on...(especially 134a systems)..the idle will go up and down as the compressor cycles on and off.

)The fact that thge engine idle fluctuates when it is cold indicates that the Fast Idle THermo Valve is out of adjustment.
This valve is located ot the front of the intake manifold on the driver's side just below the accelerator cable. To adjust it, wait until the engine is cold (best to do it first thing in the morning).
Remove the two screws holding the cover on and start the engine. There is a brass needle sticking up through a plastic ring that has two slots in it. With the engine idle fluctuating, use a thin flat blade screwdriver to SLOWLY turn the ring CLOCKWISE
until the idle stabilizes. Once done. put the cover back on withg the two screws and you should be done.