Can't catch a break! SR20DET Crazy high idle

[piman2k]

Morning

So H15 is yet again being temperamental. Last night I drove from H-Dev (75 miles) faultlessly (excluding transmission). I stopped at the house to discover a 1200-1700rpm hunting idle. Being pitch black there was nothing I could look at.

This morning on cold start the idle is 2500rpm. Two hours later back at my garage it's 3000rpm.

Any ideas what is going on?

Can't see any obvious vac leaks, hosework looks ok.

Tested the IACV power supply. 12V. Ok
Tested the IACV resistance. 10 Ohms. Ok.
Unplug the IACV and the revs drop off around 400rpm.

Unplug the TPS and there's no difference.

As the car warms the revs are very very gradually wearing off but I can't sit at 3k rpm in the garage. And I'm reluctant to play with the IACV idle screw as the idle has been fine since mapping.

Any ideas are welcomed.

[enzo]

What about the fast idle cam, is it still contacting the throttle pulley when it's warm?
Maybe there's no coolant flowing to it so it's not actually pushing the cam off.

[piman2k]

This is on my list as well but I can't figure out 3100rpm from that. I got a few snaps of it's position I'll upload in a bit.

[Ross.]

This sounds stupid Ryan, but have you checked all your earths? My old S14a had the same problem, idle was all over the place. I noticed a loose earth, sorted it not thinking it would fix the idle and it was fine after that. It was the weirdest thing, but it was fine after that! What about the coolant temp sensor?

[800bhp]

is the throttle butterfly closed?

[Jez]

For it to be that high it'll be an air leak: either the throttle plate being held open or some other gap.

[piman2k]

I thought air leak, hence the first post. Frustrating.com. Soap spray across the hoses? Or vacuum?

[immy21]

I thought air leak, hence the first post. Frustrating.com. Soap spray across the hoses? Or vacuum?

That will get sucked in rather than blown out. If the leak effects idle then it must be throttle body or engine side of throttle body.
Spray carb or brake cleaner at any potential leak spots, if idle raises more then you have found your leak. Play close attention to small hoses around throttle butterfly (FPR and 2 below throttle)

[piman2k]

Cheers immy. Any ideas how to force the idle or override it so that when I start it to test it doesn't Rev it's tits off?

[ex-ctr]

theres a one way valve that can some times stick open, its push fit into rear left hand side of the cam cover, vents fumes from the engine under heavy vacuum straight into the inlet manifold

[skyshack]

theres a one way valve that can some times stick open, its push fit into rear left hand side of the cam cover, vents fumes from the engine under heavy vacuum straight into the inlet manifold

PCV valve should be open at idle - it's about max vacuum.

If it sticks it blows boost out into cam box breather.

[immy21]

Cheers immy. Any ideas how to force the idle or override it so that when I start it to test it doesn't Rev it's tits off?

A couple of ways, you can turn the large philipps screw on the IACV, mark it before you turn it so you can return it to original position. I don't think this will work though, as the ecu is probably chasing a lower idle and already closed off the IACV. ECU will show the % IACV operation value.
The other, there is a tiny lock nut and adjustable grub screw on the throttle body for the cold start, the metal plate has 2 lines which line up with the pin, 1 line for hot and one for cold. This is what lifts the throttle a tiny bit open when engine is cold, you could try adjusting it towards the hot setting (when cold) to close up the throttle and reduce idle. Give you a chance to see if it's sticky too. iirc you can push it with your hand against the spring before you fiddle with any screws, try that and see if it drops idle.
If you need pics let me know and I'l take some tomorrow, I'l be working on my car anyway.

I would try ex-ctr's suggestion first as it's a 1 min job to check.

Oh, one more thing. take the intercooler cold pipe off so you can look at the trottle body, as I'm typing this I just remembered I once had exactly the same problem as you, turned out I forgot to remove kitchen towel from the throttle body (to prevent dirt entering when pipe was detached), it got sucked and stuck under the throttle body wedging it open. oops

On my way home that night I had to switch the engine off approaching a red light so not to attract the attention of a fully marked up disco in front of me. As if while driving using my handbrake in a tall gear to keep the revs down wasn't enough, I didn't anticipate my ebay HID's having an epeliptic fit upon restarting at the lights. As I rolled up to my garage door I realised one had failed to reignite.
At least they didn't pull me, so yeah, check to see if your throttle is closed at rest.

[ex-ctr]

PCV valve should be open at idle - it's about max vacuum.

If it sticks it blows boost out into cam box breather.

my bad, thought they operated under higher vacuum caused by engine breaking, never ran one on my engine first thing i removed/blanked off when upping boost

[piman2k]

Thanks chaps. The thing is, it was fine before and had been for a couple hundred miles so I'm leaning to an air leak. But at the moment I can't find anything and today I can't be with the car either. It's definitely mechanical though as the PFC is still seeking the correct idle. One for the professionals.