I have a 1990 Civic Si, with the stock B16A6 engine.
Here's what happens:
1. I shut off the engine after its all warmed up.
2. I leave it off for 3 to 5 minutes or even up to 10 minutes.
3. The next time I start the engine, it idles at 250 rpms and then eventually it will just die. If I try to give it gas at 250 rpms, the engine will just die.
4. If I wait a few seconds, and then start the engine, it might stay and idle at 500 rpms, or it might die again. After I can start the engine and get a good idle, it drives perfect.

I can start the car perfectly when the engine is cold and the idle is always perfect.

I have new spark plugs and a new fuel filter (changed about a month ago).
I checked the battery and its voltage is great 12.80 V.

What should I look at to troubleshoot this problem?

 

The ECU looks at several sensor to adjust the air/fuel and idle. Your TW (coolant temp) sensor may be sending false information. You intake air temp sensor could also be the cause. The throtle position sensor could be flaky when warm, but you state your idle is perfect at other times.

I would suggest you make sure there is no air in the cooling system and that it's full. (An air bubble could screw up the reading from the TW sensor, making the ECU think the engine is cold, and dumping too much fuel into it.) The TW and intake air temp sensors are just resistors that change in value with temperature. If you had the time and patience, you could connect an ohm meter to them when the engine is hot and watch the readings as it cools. If it suddenly jumps around, the sensor is bad.

That's where I'd start looking. One final thought, make sure it's not something stupid like a loose screw on the rotor under the distributor cap.

 

try checking to see if your coldstart valve and that area isnt leaking any coolant. or anything is diconected. that valve ***** with your mind if its going bad. definatly has bearing on how your car idles. mine was bad on my 93si motor and i couldnt figure out why my idle was all skrewed up for a month..hopfully this info can help in some way

 

Thanks.. Any more tips?
I'll need to start troubleshooting this on the weekend. I'm too busy during the week.
Its just odd that the idle is messed up only after startup and the rest of the times it idles fine.

 

Maybe a cat is crawling under your hood (when your engine is warm) to keep warm and is blocking your intake! Hate when that happens.

 

Before you do anything,get an intake cleaner and clean your throttle plate,itll mess up your idle like that if its dirty in there.

 

I've heard of this problem alot with 90-91 CRX's. Then last summer it happened to my 90 CRX Si. All the same symptoms you just described.
Well I did a little research on Resource.crx.org and found out it was the main relay (located under the dash on the drivers side behind the change drawer). I am not too sure how similar 90-91 CRX's and 90-91 Civic Hatch's are, and I don't know if the main relay is your problem, but it just sounded all too familiar for me not to post anything. Here is a link on how to replace the main relay just incase...
http://www.angelfire.com/ny5/7psicrx...placement.html
Hope that helps!
Later On!
-Kin

 

The main relay powers up the injectors and the fuel pump. If the car is running, it's unlikely to be the problem since it's either making contacts or it's not. That's not to say it couldn't be crappy contacts, though. The relay is mounted above the hood release lever. It's a PIA to get out, but if you're ambitious, it wouldn't hurt to resolder the circuit board contacts on it just to rule it out as the problem.