Great news! I got the exhaust centre section replaced (coroded) and
while I was there I asked the garage to replace the main fuel relay
because I also had an intermittent restart problem (once in a while
after stopping the engine to pop into a shop it wouldn't restart for
about a minute).
Now my rough idle, intermittent stall and intermittent restart problems
are all gone ! Dont know if it was the exhaust or main relay that fixed
it. Hope this helps someone else out !


Chris wrote:
> I've had a stalling problem for the past year on my '93 Prelude Si
> VTEC.
> It idles rough and sometimes stalls when warm and the revs drop
> (typically when stopping for traffic lights).
> The distributor recently failed and I was gutted that a replacement
> didn't help me with the stalling problem.
>
> So, from searching the web I reckon it might be the Idle Air Control
> (IAC) valve (aka EACV Electronic Air Control Valve).
>
> Can someone please tell me from this photo where this component is
> located?
> http://63.218.54.74/prelude/airvalves.jpg (200KB)
>
> I've placed a red X where I think it is located.
> Also, where is the fast idle control valve ?
>
> While we're at it, is the EGR valve where I've marked EGR??? ?
> And, finally what is the black think where I've written "What is this
> ?"
>
>
> In case anyone is interested in helping me further, this link points
> to a
> movie of the rough idle.
>
> http://63.218.54.74/prelude/roughidle.mpg (2MB)
>
> I increase the revs 3 times
> 1. Initially the fan is on so it's quite noisy (ignore this one).
> 2. Fan stops and noise level drops. I pull throttle chord again,
> engine runs ok.
> 3. I pull throttle chord the third time, idle drops very low and
> engine almost stalls, then revs pick up to normal again. When on the
> road it sometimes actually stalls (a few times a week). There is also
> a rattle, this is coming from a vibrating heat sheild.
>
>
> Notes:
> There is one ECU code (code 12 - EGR lift valve). Local dealer has
> checked vacuum and thinks it might be a bad ECU or bad wiring but
> hasn't been able to find out for sure.
> Local dealer hasn't been able to successfully diagnose the stalling
> problem and after 2 visits has sent me home with a new battery and
> distributor (which had failed).

 

Chris wrote:
> because I also had an intermittent restart problem (once in a while
> after stopping the engine to pop into a shop it wouldn't restart for
> about a minute).
sounds like the main relay, yes?