1998 honda civic cx HB

B16a gen 2 swap
virgin p72 obd2a ecu
end of the week i am switching over to a obd1 p30)

so, i recently changed my alternator and battery, car was having small surging issues on cold starts between 1300 and 1500 rpm, when driving i could feel the surge to below or over that rm range. decided to clean the throttle body, ficv, and iacv.
cleaned throttle body, ficv, and iacv, were pretty much immaculate. the ficv piston though was prbly unscrewed about half way, screwed her back down reinstalled everything.

upon installation cold start was about about 1000 and warm idle was just barely 600, any kind of load would nearly stall the car out.
I dislocated the iacv cable, reset the idle screw so it idles with no load, no iacv sensor @ 650 +/- 50 rpm.

turned car off, reset ecu via obd2 scanner, removed hazard fuse, waited about 30 seconds, reinstalled hazard.
started car, cold idle was 2000 rpm and dropped to about 1600 rpm 10-15 seconds after.

got warm and went to about 700 ish, but was surging again, 700-1000, up and down.

i touched the throttle, and it shot up to 2000 rpm and drastically is surging up and down between 2000 and 2500 rpm.

if it ouch the throttle again say raise it to about 3000 rpm it sits there fora second, drops to 2000, hold for a second and then slowly drops to 800 then surge idles very lightly.

things i have done already:
-finger over iacv and ficv holes.
iacv stalls on cold when choked so im guessing it is alright, i can feel air sucking slightly from ficv when cold and nothing when hot, im guessing that is ok as well.

-i don't wanna touch the idle screw until i get the surging stopped other wise i feel like i could just confuse things. but it has been adjusted since the reinstall.

could an air pocket in the coolant system cause this much of an idle issue?

could tightening the piston in the ficv all the way down (snug NOT torqued im not dumb)
cause this problem?

checked for vacuum leaks, could not find any

placed hand over throttle body mouth, car stalls so im guessing no leaks, via gaskets etc.

what else could this be? any ideas of what else to check.

( iacv has been converted to a 2 wire from a 3 wire properly via orange wire cut and a12-a14 wires switched at the ecu.)

symptoms i know of, i am throwing a iat sensor code, giving me a high voltage reading.
i know to fix this BUT i really feel like the iat sensor would not throw it off this bad consider it was giving me this code before this insane surging started.

any ideas would be helpful

 

air pocket, incorrect ecu. i would try the correct ecu first before anything else.

 

i am in the process of bleeding the coolant now.

the ecu if someone could help me understand as to why that would cause such a problem??

a gsr ecu either way i feel like should not idle like that.

haynes says cold idle on a b16 is about 1600, warm is 700 on load between 780-800.
so ecu confuses me, either way ill know when it shows but i still need to get the idle fixed, i feel like and ecu may fix idle rpm but not surging.

any other idea's?

 

Use your finger to cover the hole inside the throttle body leading to the IACV or FITV. Does covering either hole stop the idle surge?

If not, you have an intake air or vacuum leak.

 

(i ahve been researching, search engines, forums, etc. for idea's decided to post because im running out of idea's as to the problem)
no it does not, the top hole though causes the car to die, being the hole to the iacv. so im assuming it is working correctly from the behavior?

*update*

did a coolant bleed ( i did not replace coolant, just bled it)

idle seems more normal now, cold was 1600 with a slow decrease as warming down to 800rpm. is a little high for no load but a step forward.

no the issues it when i give it slight throttle, to about 200p rpm and let off the throttle, the rpms drop to 1100, surge 1100,1200,1100,1200, then back down to 800.

so to be clear.


800-throttle-2000-throttle off-prm drop-1100-1200-1100-1200-1100-1200-900-800 steady idle.

what in the world???

and what does it mean by covering the top hole (iacv) when the car is at operating temp. it drops 100 rpm to about 710-740 idealy where it should be with no load, it my idle just set wrong?

 

You have the wrong ECU for your engine, but the OBD2a P72 ECU base idle speed is 480 rpm not 650 rpm.

 

well the only reason why i set it there was my obd2a to obd1 conversion will be here in 3 days and i have the p30 ecu sitting right here, i set it for 650 for the p30 install.

SO from that, do you think an ecu swap will fix this problem?

and i just checked by putting my finger over the top hole, reving the engine, idles up and down smoothly. no finger on hole it has the small surge problem at 1100 then goes back to 800

 

If the P72 ECU is installed when adjusting the base idle, then why would you set the base idle speed to that of the P30 ECU?

And I do agree with Kyden that you should first install the correct ECU.

 

well my logic was, set the idle according to the p30, so when the p30 is installed easy going,

but i do agree with out and just went to set it for the p72, problem is after dislocating the iacv, the idle will not go under 800 rpm for base idle, screw was as far in as possible.

so right now, even if i want to set it for 480, i simply cannot. given i feel 480 is way to low for a b16, it was near stalling at 500 rpm

 

The engine-ECU mismatch has come back to bite you. The ECU expects something that the engine cannot deliver.

 

ahh, well i mean the idle is much better compared to before so thank you for your help,


couple of days and the ecu harness shall be here then testing all this out shall confirm everything or not. either way i will be posting back here whether it works or not.

my last question though is the surging. my finger over the iacv hole idles smooth and rpm tranistion is smooth, no finger over the hole, there is the flucuation at 1100 for a few seconds. you think this is ecu as well?

thnx for the help either way greatly appreciated

 

I think the problem is the ECU, which is unsuccessfully trying to lower the idle speed due to the mismatched engine.

Other possibilities are a faulty ECT sensor or TPS.

 

do you know what manual that info is in for a b16 ( the tps and ect) i should check them either way. but you/kyden are right ill wait for the ecu and see what changes.

it is drivable now, so i would say this is 50% fixed sorta.

grab a new iat sensor, throw in the p30 and i shall be posting back i a couple days with results and ill check the ect and tps as well.

 

ECT sensor - 200-400 Ohms with engine fully warmed up

TPS - 0.5V output at closed throttle, ~4.5V output at WOT

 

thank you kindly.

 

Alright, so it's friday, got my ecu harness (obd2a-obd1).

installed the jdm p30 ecu

installed a different iacv

double checked the fitv ( tightened all the way down the back off 1/4 turn)

fixed the iat sensor (it was mangled i am assuming from the previous owner having the iacv and iat plugs backwards)

the car idles much much better now but there is still problem.

cold idle is 1600 that is perfect BUT!!

warm idle is 900-1000 and whenever i touch the pedal or put her in neutral the rpm's fluctuate at 1100 and 1200 for a couple seconds.

so same problem just not as bad.

throttle on- 2000 rpm-throttle off- rpm drop- 1200-1100-1200-1100-1200-1100-1000-900 idle. idle is high i cannot seem to back it off anymore.

so what else could this be?

btw here is the iat sensor, i was like... WOH!!! :O

 

Try bleeding the cooling system.

Is the FITV pulling any air when the engine is fully warmed up?

 

will be flushing and bleeding cooling system this weekend.

the FITV is NOT pulling air when the engine is warmed up. BUT I am gonna double check this just to confirm again it is not just to be 100%
double checked all vacuum lines as well.

i feel like the coolant flush/bleed may solve this BUT i wanna keep this open just incase it is not, as the high warm idle is still a little curious being at 1000rm and unable to drop it lower with a proper idle adjustment, according to the haynes manual.

i should note as well, car does stall out and die with my hand over the throttle body, so no leaks, car drops idle by about 240 +/- rpm when i block off the iacv hole inside the throttle body mouth, so i am guessing that is working correctly AND i made sure the throttle cable deflection is about 10mm and is not holding the throttle open.

 

alright coolant system is bled. still hunts for a few seconds around 1100-1200

ill be making a video tonight or tomorrow sometime so you guys can see exactly what it is doing.
everything seems normal, but letting off the gas when it is around the 1100 mark it is not smooth and although does not seem to be effecting DD, it is very annoying