1999 2.0 litre Nubira idling at 2000-3000rpm????

[Homer]

Hi all, hope someone here can shed some light on my dilemma?
Ive got 2 (yes 2) Nubiras, my sedan (108000kms) and my wife's is an estate (150,000kms). Both have identical 2.0 litre EFI engines.
Last Saturday night my 17 year old son was driving his mothers car and got it bogged. I dont want to know how!
After getting it pulled out he was driving it home when it stopped. I towed it home the next day and found the timing belt was loose.
The bearing in one of the timing belt idler pulleys had collapsed allowing the valve timing to slip out of whack. The result, 16 bent valves!
Ok so I pull the head off, replace the 16 valves, lap the seats, fit new valve stem seals and a new head gasket. Not my first rodeo, I bought mine with a busted timing belt and rebuilt the head on that one as well'
So, I get it all back together, start it up and vroom!
Great, it runs. Only trouble is, its idling at between 2000 and 3000 rpm!
Ive triple checked the valve timing, and its spot on.
I disconnected the throttle cable, no better.
Ive cleaned and tested the IACV. No better.
To be sure I just swapped the throttle bodies on the two cars, and problem persists on this one. Mine idles fine Its definitely not the throttle body, IACV or TPS.
I'm thinking its an engine management (computer) issue. Unfortunately, while I'm a fair mechanic Im an electronic imbecile!
Can anyone steer me towards a solution, please?
Thanks
Homer

[benzino]

if the coolant sensor is disconnected, it will idle at 3000rpm (and if I were you, I'd check this connection first as it's right at the passenger side of the head)
a disconnected oxygen sensor will also cause a high idle but only about 1500-1700rpm

could it also be possible that wires were damaged when the car was bogged?

also have you done the idle relearn procedure? I assume you left the battery disconnected when you did the head?

[benzino]

Idle Learn Procedure:
1. Ignition on for 5 sec.
2. Ign. off for 5 sec.
3. Ign. on for 5 sec.
4. Start the engine in P/N
5. Allow the engine to run 'til operating temp. is reached.
6. Turn a/c on for 10 sec.
7. Turn a/c off for 10 sec.
8. If auto. put your foot on the brake and shift to D
9. Turn a/c on for 10 sec.
10. turn a/c off for 10 sec.
11. Turn ign. off

[Homer]

Thanks Benzino, the coolant sensor is plugged in, but l will check its connected properly. I'll also check the O2 sensor. l had a go at the idle learn procedure, which dropped the idle revs from about 3000 to 2000 rpm, so l think l'm on the right track.

[NubiraTurbo]

There is only one thing that can make an engine idle higher by that much. Air. It's getting more air from somewhere inside the intake manifold. Either the idle control valve or a leak. (Vacuum pipe, brake booster pipe, etc.) Try disconnecting the idle control valve while ignition is off and start it. Also measure the vacuum in the intake manifold. It will probably be less than normal. Since you have swapped the throttle body, i doubt that it is the idle control valve itself, more likely the the wiring or ecu deliberately forcing it open. I know that a fully open valve will set the idle to about 2500-3000 rpm.

[MMamdouh]

i am more inclined towards a vaccum leak diagnoses as well

only time i had similar issue i had a faulty TPS but you already covered that bit...

it has to be a significant leak to raise the RPMs that much...make sure the brake booster hose is not cracked or so

MMamdouh