91 SI won't idle when warm

Need some help here. I have a 91 SI Civic with the 1.6. The car starts right up but after the car gets warm and the idle comes down the car will die. I can keep it running by feathering the throttle but once released the car will die. I just replaced the O2 sensor and it seemed to run better but it has not fixed the problem. Thanks in advance for any and all help.

check engine light?

My guess would be either the throttle position sensor or the IAT not sending the correct signal... either way, they're easily fixed/cleaned/replaced.

No check engine light. Thanks for the reply.

EACV could be dirty or broken, it happens to alot of people. Do a quick search of this forum to find plenty of info on it. If the car ran fine before then I wouldnt put much money on the idle adjustment screw, but it could have moved.

yeah i was gonna say try to adjust your idle screw if it was dying on you..

One more thing I didn't post was that when it is getting warm and the idle is coming down, if you do a quick tap on the gas when the idle comes down, it will just about die, then surge back up a little, then back down but not as far, and then even out. I don't know if I am explaining it right but it is like a surge up and down. Thanks again for the replies, I wanted to get some knowledgeable opinions before just replacing everything that might be the problem.

that's normally cam or ignition timing, that causes it to die when you hit the gas. it's basically that the timing is probably far enough off that it's "flooding" and when the engine spins over a couple times to get the excess fuel out, it goes back to a stoichiometric a/f ratio, and will burn better, so it "surges" up in RPM.. this usually takes just a second, as the engine is spinning quite fast, and expelling excess fuel into the exhaust at every exhaust stroke.

When you let the car warm up, and you're driving it around, feel down by the shifter on the floor, and up by the floor vents.. if your floor is hotter than normal, that means your cat is getting hot, it's either plugged or you're dumping fuel.

I second cleaning the EACV (12mm bolts I believe on backside of intake manifold. The little screen gets carbon deposited and then the dirty eacv cannot do its job (idle the engine).

Also, check all the hoses going to and from the intake manifold for cracks and wear. A trick is to spray the hoses with water and see where the bubbles form. You can use duct tape to temporarily fix these hoses.

just an addition to turtle's post... warm water and light soap mix tends to stick to the lines better, especially underneath, if there was a pinhole or something, and the bubbles are bigger, and easier to see.

Ok, pulled and cleaned the EACV (twice) and checked the vac lines. No affect. Still doing the same thing. Starts great, rungs great, warms up,,, dies. Thanks for the advice, I will keep checking.

Well, it could be a number of things. But before you start spending money on stuff you don't need, start with the cheapest/easiest things first. When's the last time you changed the spark plugs? Check all grounds and make sure they're clean and tight. Check your rotor button inside the distributor to make sure it isn't loose. If it comes undone, you'll be stranded somewhere shaking your head why it won't start at all. Check the power going to the ignitor (square thing on bottom of distributor) and coil itself. This link is for the Helms manual and it should help you out a lot...
http://www.crxpower.net/~silverkorn/manuals/CRX_Workshop_Manual.pdf

Ok, it's been raining and cold here in the Seattle area for months and there are motorcycles in the garage so I haven't been able to work on it. Its nice now so I adjusted the idle to keep it running and drove it to my father in laws so we could adjust the valves (yea, I should have mentioned they were ticking after a recent head rebuild). Turns out that there is a broken valve spring. The new part should be in Friday and we will do the install this weekend. I will post results in case it can help someone else. Thanks again for all the suggestions and advice.

Yup, that was it. One of the #3 exhaust valve springs. Running strong and smooth. Thanks again.

Well that would explain alot..its a vacuum leak. Cant figure out why it wouldnt idle only while hot but anyway, at least you got it fixed...Oh btw, reading a few posts up. The EACV doesnt have any vacuum lines. it has coolant lines. Maybe you had the wrong sensor.

try replacing the IAC valve

well, guess I shoulda read the whole thread huh, well good job dude, glad you found it, that woulda been my other guess.