Hey guys im new here, i heard this is the best place to ask for help.

I got a 91 CRX with a JDM d15b vtec.

I finally got it running yesterday and everything seems to be working fine EXCEPT..

when i start the car it idles at 1200 which is normal because the computer reads the engine is cold. after about 5 min the temp gauge starts to go up slowly and my idles drops down to 800 where I have it set at. So everything is working so far.. untill i start driving.. As soon as i begin driving the car the temp gauge suddenly drops down to cold. and my idle is at 1200 again. So the computer is reading that my engine is cold.. ????? i thought maybe a connection was loose or something so I checked everything. and started it up.

again it takes about 5 min for the temp guage to start to go up and the idle to drop down to normal. but as soon as i begin driving the temp guage drops to the bottom, and when i stop to check the idle its at 1200rpm again.

anyone have any idea why its doing this. Thanks

 

It could be your thermostat. Would you know if it's the original? Pretty easy to change.

 

How new is your thermostat? It could be your temp sending unit going out too.

 

i dont think it would be the thermostat.. im pretty sure it works fine. if it didnt, why would it cause my temp gauge to not work at all when im driving, but only work when the car is idling.. i drove the car for about 20 miles and the temp gauge never moved at all. it stayed at cold the whole time. as soon as i park it and let it idle for about 5-8 min the temp gauge starts to go up slowly.. along with my idle dropping to normal rpm at 800.

 

bleed ur coolant system sounds like u have a nice air bubble in there

 

maybe.. but after 20 min of driving the temp gauge never moved a tiny bit from cold. it stayed at the lowest possible spot on the gauge the whole time.

 

Sounds like the gauge or sending unit is bad or you hooked up the coolant temp sensor to the temp sending unit. Did you do a lot of wiring recently? I would get a mechanical gauge and hook it up to make sure the temp reading is even correct.

 

I know the gauge works fine, it did with the stock engine. my buddy helped alot with the wiring since i dont know much about it. what is the sending unit?

So far this is what i know of.. the sensor in the back of the engine by the oil filter is the sensor for the radiator fan. then there is 2 sensors by the distributor. one is a 1 wire sensor the other is a 2 wire sensor. im guessing one is for the gauge, the other for the ecu?

this is so confusing and doesnt make any sense. i start the car and after a few min the temp guage starts to go up slowly. everything seems to be fine. but AS SOON as i start driving the car the temp gauge drops to cold. then my idle goes back up to about 1200 instead of 800.

 

You are mistaken the one on the rear of the block is for the engine oil pressure. The coolant temp sensor and temperature sending unit are almost always on the head for pretty much all motors. There are reasons but I am not explaining them right now. What controls the radiator fan and ECU is the coolant temp sender. The temp sender is only for the gauge. The coolant sender is the 2 wire sensor. The temp sender is 1 wire. It almost sounds as if the sender is bad or wiring is crossed. I can't remember if the coolant temp sender is normally open or closed. Either way put a mechanical gauge on it and go from there stop trying to do bench (a.k.a. H-T) testing and do some testing on the car. That is the only real way to figure it out. Or you could get a multi-meter and test resistance and voltage...

 

I started my car cold and felt the lower radiator hose and after about 2 min it was already warm... so i took it out and sure enough. it was stuck open halfway. it was closed at an angle, half open/half closed. So i put a new one on started it up. let it get warm, drove it around. perfect. temp gauge reads a little less then halfway and stays there...


but as always with my luck as soon as i fix 1 thing, something else goes wrong. my idle was surging from 500-1200 rpm. Im guessing its the iacv right? I unplugged it and the idle went back to normal again. that means my iacv is crap right?

and then.. I was reving it a little and i noticed ALOT of blue smoke coming out of the exhaust, and it almost looked as if gas was shooting out as well??? you could almost see it in the air too like a hazy mist.. It has not done this until now. does it have something to do with the engine being warm now so the computer is changing the fuel/air mixture? I know it cant be burning oil because it never did. and now all of a sudden after i switch to a new thermostat its doing this...

 

anyone?

 

Blue smoke = burning oil
White smoke = burning coolant
Black smoke= too rich

Fixing the thermostat (in a somewhat long shot kind of way) could now let your motor warm up enough to let oils past the rings or valve stem seals. When before it was keeping it cool enough to not burn oil... Somethings toast...

 

hmmm. would a compression test prove if its burning oil.. last time i checked all 4 cylinders were 180-190. that was about 200 miles ago..

any idea on this idle issue? like i said the idle starts bouncing when the engine is warm. from 800-1200rpm. but if i unplug my iacv sensor it idles perfect at 800rpm.. does this mean my iacv is bad?

 

No a compression test would not "prove" it was burning oil. If blue smoke is coming out then it is either going past the valve stem seals or the piston rings and possibly the head gasket.

Sounds like the IACV needs cleaned out or is bad. Check the FAQ there is a good thread on this in there.

Also I have a hard time believing a D15 has 180-190 psi in the cylinders, they have around 9:1 compression...

 

alright guys a lil update. I took off my intake and started the car cold. It idles at about 1600. NOTE: temp here in Minnesota is about 20 degrees. So thats probably normal for it to idle like that at cold. I can feel air sucking in both the IACV hole and the FITV hole on my TB. after a few minutes the idle will slowly drop and drop until its at about 1000rpm and it stays there. There is no longer any air sucking through the FITV hole on the TB. So that means my FITV is working properly. So just off curiosity i felt my lower rad hose and its cold. the temp gauge is about 1/4 the way up. I keept letting it idle and checking the lower rad hose... still feels cold. so i waited... 20 min goes by and the lower rad hose is still cold.. hmmm. I put a brand new thermostat in it the other day so it should work. (note: when i put the thermostat in the other day i didnt bother to check the lower rad hose if it even got warm) i assumed it did and now i see it does not. 25 min since i started the car the lower rad hose is still cold. the temp gauge sat right under halfway. something is wrong right? it shouldn't take that long for a thermostat to open.. I did notice tho..as soon as i turn the heat on, that anoying idling problem begins. it goes from 500- 1500 rpm. for about 30 seconds then it goes back to 1000rpm again.

i really dont know what to do at this point.. any ideas?