engine light is on and wont idle.

After doing a engine swap, I found that my car once its warmed up wont idle, and after it gets to near running temp, the check engine light comes on. Other than that it runs great. Would this be caused by the o2 sensor on my exhoust maybe not working properly? or is there any other opinions? thanks alot.

Check the CEL code. And what do you mean it won't idle, it has an unstable idle?

Whenever the clutch is in or its out of gear and just left sitting there, after it has reached running temp, it wont idle. But while its warming up with the auto choke on it will idle fine. How do i check the CEL code?

You mean like, the rpms surge?

Whatever you call it when instead of when your rpms go down and stop at about 800rpm, it just goes to zero and stalls.

I had a similar problem with my 4th gen only my rpms would surge, but my engine light still came on at running temp. Anyway it turned out that I had a bad vacuum line and that fixed it right up.

do you know which vacume line it would be? Thats a very posible problem, concidering I just changed engines and maybe didnt hook up a vacume line properly.

Please read this and help me if you can!!!

I rebuilt my 1988 prelude engine and am having problems with mixture! It is a B20A5 engine,fuel injection 2.0l. Symptoms:

With no check engine light:

-runs rough
-as soon as it hits 3750 rpm it has a definate iBIG JUMP in horse power!!!!
-smells like it runs rich


After check engine light comes on:

-runs better!!!
-no big jump in hp @ 3750 rpm
-does not smell as rich

Apon rebuild I replaced the o2 sensors with new NGK o2 sensors, new distributor cap and rotor, plugs(platinum), ect...

please help me !!!!!!!!!!!!!! The biggest thing I noticed is the gain of HP when the light is off (weird)????? Could it be the o2 sensors ...egr valve??? pcv valve???? I confused????

Thank you
Steve