kanjozoku

hi, i've been having low idle at ~500rpm but it is supposed to go at 750+-50 rpm at idle according to manual (1993 civic CX CDM). timing was checked and is spot on 16+-2 BTDC. replaced O2 sensor (was getting cel 1 now gone), replaced PCV valve, replaced fuel filter, replaced air filter, replaced spark plugs, replaced spark plug wires, replaced iacv, cleaned TB countless times, check for vacuum leaks. I did try to adjust the idle with the adjusting screw but even with that screw completely off my idle still low at ~600 rpm. i did follow the manual steps to adjust, i.e. i disconnect iacv and then adjust screw, and then reconnect iacv and reset ecu by taking off fuse 7.5A under hood fuse box. sometimes it looks decent at ~700rpm but is not constant. it will drop down again to 500rpm after sometime, then go back to 600rpm then back to 500 etc. i have been having acceleration issues, a delay, hold back, hesitation. also did compression test. 170-180psi accross all cylinders. i dont think it has something to do with fitv because this one seems to work fine. when car is cold idle will be 1000rpm since the fitv is open. then warms up and idle gets low at 500rpm.

today i tested my tps, it read 0.47v at closed throttle and 4.47 at wot. manual says should be 0.5v at closed and 4.5v at wot. but could that small 0.03v difference be that significant as in having low idle and bad acceleration ?

maybe ill just replace my tps - i got a new one since i thought it was the problem but after today not sure anymore...

also cooling system is completely bled. used lisle funnel to bleed it. engine temp is perfect just a little below mid-mark and coolant level is spot on too at MAX mark in coolant overflow tank.
did change oil and filter lately too. put exactly specified amount and grade oil.

also did a regane gumout fuel clean through fuel tank... did a seafoam clean too. engine seems healthy overall and it has around 100k miles not even, maybe 90-95k.

this is a stock car, engine never swaped either.

one thing i notice when trying to adjust screw, is that while the car is running with iacv disconnected, i try to make it rev higher but as soon as it hits 1k rpm or so, the rev start jumping up and down. even if im not moving the pedal at all, just holding it to the point where it starts doing that. then i let it off and goes back to low idle 500 rpm. that happens while iac is disconnected and im trying to adjust. honda manual says to rev the engine to 1.5k rpm and slowly let the pedal till idle settles and then adjust screw. could be good information to diagnose the problem... i thought tps bad but now that i tested and got decent results im not so sure.

so what could be giving me low idle and acceleration hesitation ? any ideas ?

thanks guys

Former User

500 rpms when engine is cold? If so, clean the FITV.

TomCat39

In addition to Ron's question.

How are you measuring RPM of the engine?

mk378

+1 don't trust a stock dash tach to measure idle rpm accurately. If the engine is not shaking or stalling out, idle speed is not too low.

Warm up the engine turn all electrical devices off, unplug the IACV then adjust the air screw (big slotted screw valve in the top of the throttle body, NOT the little screw that stops the throttle plate) for a lower than normal idle (420 rpm if you have a good tach, otherwise adjust until it starts to shake and threaten to stall out). When you re-plug the IACV it should pick up to normal idle. Unplugging the IACV will turn on the CEL with a code 14 which you can ignore.

kanjozoku

no i said when engine is cold rpm is 1000 which is why i dont think fitv is bad. it's after the engine is warmed that rpm drops low 500.

Former User

Is the air passage clogged between IACV and IM?

kanjozoku

i am using dash's rpm... i trusted it lol. you guys made me think it could be the tach that is wrong. i have an external tach though. will test it out this weekend.

however, even if the tach is wrong and my idle is ok (which i doubt), why am i getting hesitating acceleration and also the symptom i described about the rpm jumping while reving up to 1k during adjustment (i.e. with iacv disconnected) ?

dont think so as i cleaned TB and seafoamed it too

Former User

Is the engine showing any symptoms of a low idle speed like vibration or stalling?

The other issues sound like basic engine misfiring. Have you done a tune up on the engine?

You should verify that it's open, assuming that you actually have an idle problem.

kanjozoku

if timing engine to spot on 16+-2 BTDC (spec), changing oil to spec, oil filter, fuel filter, air filter, pcv valve, o2 sensor, spark plugs, spark plug wires, flushing and bleeding cooling system is considered a tune up, then yes. and no the engine isnt showing stalling or vibration but i just know it idles low and i dont think my rpm gauge is faulty. anyways ill be testing an external tach this week end and see.

i guess im taking off the TB again and cleaning it... and replacing the TPS while im at it. doing it this week end...

could the pcv line be clogged at the breathing chamber or something ??

Former User

You didn't mention distributor cap and rotor. Did you install the NGK plug indicated in the owner's manual?

Don't replace anymore parts until you bleed the cooling system properly and thoroughly.

https://honda-tech.com/forums/honda-.../#post38664177

kanjozoku

yes installed ngk zfr5f-11

also i bleed my system with lisle funnel which i find better than using the bleed bolt procedure which i did in the past and there is always air bubbles no matter what. my cooling system is perfect right now. i bled it 100%. fluid is spot on MAX mark in overflow tank. coolant temps are perfectly set just a little below the midmark on temp gauge... trust me, i tuned it good. i think it's either the tps or the pcv line clogged... by the way, do you know if there is supposed to be noticeable vacuum from the engine valve cover vaccum line? last time i checked there wasnt noticeable sucking vacuum from this line. this is why i think i might have a clogged pcv line at the breathing chamber or between breathing chamber and pcv.......

by the way i forgot to mention but yes, i did indeed replace the distributor. got a brand new dizzy for $75... including rotor and cap and coil... i mean the whole dizzy is new. so yeah tuned pretty good right now.

Former User

Properly gapped?

Is there still an idle surge like seen in video?

Are any CEL codes currently thrown?

kanjozoku

yes they all 1mm gapped i measured twice each spark plug.

cap and rotor, well they are good i mean it's an OEM new distributor. i inspected it and everything looks fine, i mean it works fine too.

only surge is when i disconnected iacv and then rev engine over to 1000 rpm. when it get to 1000 rpm it starts surging up down up down, then i bring rpm back below 1000 at say 900 and engine idles normal. but the honda manual says that when iacv disconnected, you should bring rpm high to like 1.5k and then slowly depress the pedal for it to settle at the normal idle, and from then on you go and adjust the screw. but me i try to rev it to over 1k but the surging appears and then when i release it, the idle settles at 500... think my tps is f*cked. but at the same time i tested it today and got reasonable results...

btw no cel codes. i had a O2 cel code coming on at times before, but changed new O2 and now its gone and never came back.

Former User

Are there any problems, such as the surging problem at 1k rpm, when the IACV is connected?

If so, did you check for new CEL codes at that time or after bleeding cooling system in video?

kanjozoku

no, there are no surging problems when iacv connected........

Former User

So what's the problem? This also rules out a TPS issue.

Please answer all questions.

kanjozoku

wait, now that i think, there is small surging when iacv is connected. i feel it sometimes when at a stop light the engine goes up down but its very minor, unlike when iacv is disconnect and reved to 1k.
however, this could be cause by a bad tps ? anyways i tested the tps voltage today and got 0.47v closed thrtottle and 4.47 wot. also got 4.96v feed line. those results are kinda reasonable. so im not sure if my tps is bad...could it be my map sensor ?

Former User

Please don't mix old and new information. Currently, since replacing the ECT sensor and switch and bleeding the cooling system, what problems have you observed with the IACV connected?

Please also return to post #15 and answer all questions.

kanjozoku

low idle
hesitating acceleration

no surging problem at 1k rpm with iacv connected

no new cels - no cels at all

Former User

How do you know the idle is low?

Hesitation - Have checked/adjusted the ignition timing?

TomCat39

1mm is under gapped:



It's actually better to have them slightly over gapped then under gapped. It exposed more spark to the air/fuel mixture, while under gapping obscures more of the spark from the mixture.

1mm is 0.039" FSM states .043" minimum or 1.1mm. My gapper only has .044" and that's what I use and have had zero issues for years. 0.044" is 1.117mm.

kanjozoku

i know idle is low because of external tach

yes adjusted timing, right now spec at 16+-2 BTDC

rechecked and now gapped at 1.1mm

still hesistation and low idle

Former User

What was the reading using an accurate tach? Was the engine fully warmed up?

Explain how you could adjust the ignition timing correctly if the idle speed is actually low? See diagram for setting the ignition timing in the FAQs sticky.

kanjozoku

yes engine warmed up reads 500-550 rpm on tach

i adjusted it with a timing light, and also as the idle was low i used a plier to hold the throttle at 1k rpm for doing so

i did both without holding the rpm and with pliers holding at 1k and for both it always settles at low idle when timed at 16+-2btdc

Former User

Okay. That's low. Do you know what spec idle speed should be? Now return to adjusting the idle speed correctly. Read diagram in FAQs sticky.

When idle is adjusted to spec, set the ignition timing properly.

Read the diagram! You did not adjust it correctly.