Hello everyone, new member here..
I've had my '89 CRX Si since 2005, it has 166K on it,
and it's always ran very well until fairly recently.

NOTE: The car has always had a low cold idle, ever since I had to block off
the unit on the back of the intake that controls the cold idle speed (IAC?)
because the idle began flaring up & down and up & down. Blocking it off
solved the flaring idle problem, since a new one was a few hundred bucks,
and finding a CRX in a boneyard is about impossible around here.
To compensate for the loss of a faster cold idle I'd just hold the engine
at about 1000 RPM for a minute or so on cold starts, no big deal.

>>> Back to the problem: The car began to have a light misfire when
the engine was cold. The miss would continue from start-up till
the temp gauge just started to move, then she'd smooth out.

I checked the plugs, cap & rotor, all were in good condition.
I replaced the plug wires, as they were about 4 yrs old.
The light misfire on cold starts continued, the only code flashing
on the ecu light was 17, which is vehicle speed sensor (VSS).
Of course a VSS was unavailable, and I doubted that a failed speed sensor
would lead to a miss that decreases & goes away as the engine warms.

As time went on, the misfire when cold got increasingly worse,
and then one day the car would barely idle, cold or warm.
I now had a code for the o2 sensor, which I replaced that evening.
Replacing the o2 sensor got it to idle again,
but the heavy miss (until the temp gauge started to move) was still there.
The only code I get at this point is still 17 (vehicle speed sensor).

Would a failed speed sensor lead to a miss that decreases
& goes away as the engine warms?

If it has a bad fuel injector, or a bad sparkplug,
wouldn't I get a code for those problems?
What would cause an '89 CRX Si to have a heavy miss that decreases
as the engine warms..?

I'm pretty handy with cars in general, but I admit I know very little about
later-model computer-controlled cars, I grew up on big old cars
with big old carbureted V8's..
All I've really done to the CRX is simple regular maintenance items.
I do like the car very much, and would like to solve this problem with it.
Thanks in advance for your input.

 

I would put the IAC back on, the computer may be trying to compensate for it missing. Also you could try cleaning your old one. After that tackle the vss.

 

I understand what you're saying, that if something's been changed the ECU might try to compensate.
The thing is: The IAC has been disabled for literally years (at least 4, if not 5),
and the car ran fine for all those years,
so it's not like I disabled the IAC and immediately thereafter it developed a miss.
But I appreciate your response. Please elaborate on cleaning the IAC..
Remove it and use carb or throttle body cleaner on it? I've never had it completely off,
do they get gummed up or carboned up & stop working right?
Is there a diaphragm in an IAC? If so, harsh cleaners could damage it (or maybe it has already failed).

Disconnecting the IAC (years ago) resulted in a low (but smooth) cold idle speed, but no misfire.
It's the heavy miss (until the temp gauge starts to move) that's a new problem and the one I'd foremost like to address..

 

While again searching the site for info,
on the "CRX & Civic FAQ Version 2.0" thread,
I saw a link with the following title:

"How to fix your idling woes! FITV IACV"

Hey that's great, I thought - Might be some very helpful info there..

But clicking the link only leads to a thread about light bulbs