i have a 1990 crx with pr4, oxygen sensor isnt connected and no check engine light so im guessing it was setup to not run one. but heres the problem, idle goes up and down at random times, maybe 1400rpm, maybe 1100, and when i start it completely cold, it idles very low and rough. makes no sense. any ideas or suggestions?

 

i meant it idles low and rough then dies, but when warm runs good, but decides to idle high at random times

 

Check your fitv as cold idle is what it is made for:
Trouble Shooting Vacuum Leaks

 

OBD1 cars are designed to run on a 4wire o2 sensor. It needs to be hooked up. If you have no CEL then something else is wrong, make sure the light comes on when you first start the car and goes off. If not the light isn't working.

 

my check engine light works just fine. my ecu isnt blinking any codes either. there arent even any wires running to the o2 sensor on the manifold...im really confused

 

what engine is it? ecu?

 

His sig says B18a and first post says pr4.

 

no one has any clue? i dont know what to do bc i feel like i should be running an o2 sensor but it seems ok. minus the idle problems it runs fine.

 

I already told you, the o2 sensor HAS to be hooked up or it will run like crap.

 

theres no o2 sensor hooked up though and it runs great. i thought i was trippin out but there really isnt one hooked up. i get 25mpg too

 

ok sorry big mistake! my stupid *** friend told me the ecu was obd1 but i jus found out there are obd0 and obd1 pr4 ecu's. so it isnt converted, but still doesnt have an o2 sensor hooked up and no codes

 

anyone know what color wire is the o2 sensor?

 

White in a grey Sheilding shroud. Its possible if you dont have the stock manifold that the O2 sensor is further downstream follow the exhaust and see if you have one.

 

i dont have one anywhere! i have the stock b18a manifold, o2 sensor is in but no wires or nothing. also the knock sensor isnt hooked up but that isnt causing a problem either. im just confused, it should be throwing codes and running bad but it isnt

 

obd0 ecu's generally don't throw o2 sensor codes. i've left mine unplugged by accident before, and the cel never came on. if you cant find the wire then worst case run a new one from the ecu, pin c16.

also, the ls does not have a knock sensor. you're probably looking at the oil temp switch. it was used in the integra to run the fan if the engine was still hot after you shut the key off. it's not needed, don't worry bout it.

 

oh well thank you so much for clearing that up! could that be why my fan is on all the time? like when my key is in the on position with the car off, the fan is on

 

it's possible that it may be related.

in this pic you'll see an empty big green connector with 2 pins sticking out. that is the coolant fan switch. the wires for your fan that are behind the block need to go to this switch, not the one currently plugged in in the picture. the person who posted that picture originally couldnt figure out why there fan wasn't working, and it was because the previous owner wired it up incorrectly to the oil temp switch.

 

there arent any wires running to that switch on mine

 

sure they're not just hanging around back there, or taped up to another harness? they would have been there originally. i can't imagine someone would have just cut the wires for it clean out.

 

theyre just loose wires?

 

pretty much. looks like this