Fast idle in park or neutral

Hi all – happy to be part of the Previa community – I never even knew what this car was until recently when I got one for quite cheap as a non-runner – I played with the throttle body and made sure there was gas and I was able to get the car started and it’s been running great
I do have one issue though – it has a high fast idle in park or neutral no matter how warm the engine is – this is causing me grief at the moment as I need to pass smog in California and they won’t let you do the test if you have a fast idle in park –
I’ve replaced the throttle position sensor and I fiddled with the throttle adjustment screws, etc. – but it just seems like it always wants to be fast idle in park – does anyone have any tips or clues for me to try out?
I have the cool 1997 Alltrak model (I think they only produced 4000 of these this year?) - with leather seats etc - she has around 220k miles and abit rough exterior and interior but every time I drive this van it puts a smile on my face
I think the idle is around 1500 - but settles down when I go into drive etc
Any help appreciated
One big clue - after I got the car, I noticed it was actually missing its ECU - I was able to get one from another 1997 Previa (that had a huge sun roof btw pretty cool) and installed - but I notice neither of my code readers detects the ecu
I don’t see a check engine light on dash
So my theory at moment is if I can get the ECU fully connected/working with the Previa - perhaps the idle will settle down. Ok thanks for any advice/wisdom

Are you sure you have the correct ecu?

Hi - well it was definitely from a 1997 Previa from junkyard - mine is a 1997 Previa
my understanding is the original one I got from this couple had someone working on an issue and that person had taken out the ECU – and then they couldn’t find it after they sold it to me – so I think the issue is there is a disconnect somewhere from the ECU to the van - and this may or may not be related to the high idle problem – I found the interest in the car, ran without major issue, even without an ECU altogether – but yeah, even after I plugged one in, I’m not getting any reading on my code readers – so my plan is to trace all the wires to the ECU and see if there’s a disconnect somewhere (I already checked all the fuses)
again, this may or may not have anything to do with a high idle issue, but it is definitely something that needs to be addressed at some point

Hiya. I just got my second Previa and I'm dealing with the same thing (except my smog guy passed me with a warning). Does yours have the supercharger? Are you ready for a bunch of very helpful people to fill you in about the IACV and "black flakes" issue. You'll have some reading to do. That's how I ended up here.

Hi thanks for sharing your input
I could be wrong, but I think all 94 to 97 previous come with the supercharger by default – but if I’m wrong, please someone correct me :-)
So yeah, I have a supercharger – I read something about the black flakes issue – when I took out the throttle body there was this metal tube connected to it – I didn’t really see anything that seemed like black flakes, but maybe I’m not doing it right – I think what I’ll do now is research more on the black flake issue
It’s strange for me to think how black flakes would be involved in a high idle – but I guess there’s something to it – thanks for pointing me in that direction again
Yeah, here in California they don’t mess around with the smog – it has to be really right for them the pass yours - I really want to get this van back on the road soon – I find that the Previa is a super cool ahead of its time van – but I also get the feeling it’s good/requires to have mechanical skills to keep it going
Mine does have 220k miles - hoping to go another 220!

Did you already find this thread?
'97 Previa RWD VERY HIGH IDLE Warm Engine

Thanks for the tip on that link – I’m now reviewing it and going to try the most likely causes first after I read through this – thanks

Did you figure out what was causing your high idle? I cleaned my throttle body, replaced the IACV, and can't find a vacuum leak. No improvement. I'm still idling around 1500 in park, 800 in drive, and getting 12-13mpg.