teddy2828

Hello folks,

i've got a 97 civic lx manual. 115.000 miles.

When i have the car idling for a few mins at normal operating temperature the engine starts rumbling. the rpms go to about 600 when it does that. normally it idles around 8 to 9. i can kinda reproduce the effect when it's not doing it by turning on the AC. when the compressor kicks in the rpms drop and it starts rumbling but it catches itself and stops. what helps is when i tap the gas just a wee little bit and the rumbling goes away.

it also is worse the colder & wetter it is outside.

i dont know if this is related but it drives sluggish and i noticed the car only gets about 16 mpg and i dont drive aggressively.

there are no CEL codes. i noticed when i replaced the air filter that there was moisture in the intake that smelled like motor oil. i dont know if thats normal or not.

thanks for reading and i hope someone can help!

Jimster480

Sounds like a issue with the IACV possibly for the idle or just an ECU issue in general. I have the same problem with my 96 EX and I have messed around with it and it seems to be an ECU issue (atleast that is what I think).

teddy2828

aw that doesnt sound good. i wonder if i can get an ecu from the junkyard switch it and see if the problem persists.

Jimster480

yea tell me if it fixes it. When i get a chance im getting one too.

fleabag

Thoroughly clean all of your electrical grounds (Bolts, Washers, eyelits) until they are shiny. Sand down (clean) aluminum mating surfaces (like the ground for transmission/thermostat, etc.) until they're shiny as well. If a part is painted (like body parts), don't sand/scrape any paint off!!!

Telecatster

Agree with fleabag and also if you haven't already remove and thoroughly clean your throttle body and IACV. Check (fuel pressure) and/or replace fuel filter if you have never replace it. Replace PCV valve if it hasn't been done in the past 10K miles.

You said it's running sluggishly as well as improper idle so could be a number of things, but test the following parts before throwing money/parts at it. Check Ron's useful links for testing https://honda-tech.com/forums/members/former-user-999573189/

Distributor's ICM , coil, cap and rotor
spark plugs
spark plug wires

teddy2828

awesome guys ill check out what you recommended. i changed the distributor cap, rotor, wires and plugs - no change.

pcv valve hasnt been changed at all. i was thinking that maybe because it's crapping out im getting a lot of crap in the air intake? is that possible?

DeLSoLRo

im having a similar issue, i replaced cap/rotor/wires/plugs, corrected timing, cleaned iacv/throttle body, replaced gas filter, replaced pcv valve, and ive noticed when I adjust the idle and I unplug the IACV the rpm's dont drop like it states it should in the haynes manual. Also I've gotten a cel code a few times that is associated with the IACV. like stated either ECU or IACV.

Jimster480

nah that wouldnt do it. I chaanged that on mine and it had no effect.

fleabag

If you have a 3 wire IACV, you're not suppose to disconnect it, but if you have a 2 wire IACV and it doesn't drop the idle, then that could mean the IACV is dirty, the idle speed is set too high (therefore adjust it) or you have a slight vacuum leak somewhere.


just because you didn't see an improvement with changing the PCV valve, it doesn't mean he won't.

Telecatster

teddy2828: The PCV valve is kind of a PITA to get to and it's much easier to replace when doing an oil change and the oil filter is off. If you shake the PCV valve and it rattles it's good, if it doesn't it clogged. It may not solve your idling issues, but either way if you haven't changed it, it's good to do so and they're only about $3 or $4 at autozone.

Even though you purchased new wires, plugs, cap and rotor you may still want to check spark strength and both coil and ICM. Usually, just cleaning the throttle body and IAVC will take care of most idle issues, but why not go the extra mile and do all things that don't cost money and hopefully improve performance.

"i was thinking that maybe because it's crapping out im getting a lot of crap in the air intake? is that possible?"

Have you checked or replaced your air filter recently? Also, it's possible you could have a vacuum leak somewhere such as fractured, split, pin-hole or missing vacuum line. If, after checking and cleaning all the given suggestions the next possibility is the first (engine side) oxygen sensor being weak or bad. Again, you definitely don' t want to throw parts and money at it first so you may want to tackle it one by one and evaluate each time.

Jimster480

well our cars have the same problem. PCV doesnt affect idle quality anyway so..

teddy2828

thank you for the input. i'll have a go at cleaning the iacv and replacing the pcv valve and then maybe check for vacuum leaks. i'll report back asap.

teddy2828

ok a little update. i made sure all the grounds were good and i followed one fog light wire that was touching the metal frame. i taped everything up and then reset the ECU by pulling the fuse and now it seems to run a bit smoother. not much just a little bit.

i checked the oil and it is way low, i had it changed maybe a thousand miles ago? the dip stick smells a bit like gasoline as well. the low oil warning light doesnt come on so i'm not sure whats going on there either.

i ran some lucas fuel injector cleaner and for the last week, whenever i started the car it sounded like it was cranking even when the engine was already running. like when you turn the ignition when the cars already running but that went away after filling up a couple of times.

one thing after another, ill post more when i'm done with the pcv valve and the iacv

fleabag

There is no low oil warning light, it's an oil pressure light and when that comes on, it's serious business. Never want to wait for that light to come on.

fleabag

Well when the car is warmed up and idling, I'd try wiggling wires that are in connectors in various places in the engine bay and see if the idle changes. Do you have a multimeter? Maybe you should check your ignition wires and measure their ohms, if they're over 25K ohms, they're bad. I think for the ignition wire running from the coil to the distributor cap it's suppose to be less than 15K ohms. How long have you owned this vehicle and when did it start doing this issue?

teddy2828

wow, fundamental misunderstanding on my part here. my previous car had a yellow low oil indicator and then the red oil pressure warning. good to know :D

the car belongs to my girlfriend. she's had it since 1998. i asked and she said it started pretty much at 100.000 miles. i went through her records and i saw that she had the input shaft bearing replaced a couple of thousand miles ago. no timing belt records though which kinda freaks me out.

fleabag

Man if you had a scangauge II, ultragauge or something that could read out fuel trims, GPH, map sensor readings, etc. that would be immensely helpful.

Btw the fact that you're getting 16mpg really scares the ever living **** out of me! 16mpg is like what you'd get if you had a bad map sensor. Do you have the service manual for this vehicle? How does the car operate with the Map sensor connected vs. disconnected? I suggest downloading the service manual for this vehicle and doing some reading for the ignition and the EFI system. But let's just assume for a moment that all of your electronic sensors are working 100% a-ok and you don't have any electrical issues...


Well then, I'd say aside from a bad o2 sensor (can't confirm due to you not having a OBD-II reader), this could be a valve lash issue, fuel pressure issue (FPR is going bad), fuel injector issue (leaky/clogged/whatever), or and I think I've read anecdotally that if the timing belt is going out on these cars, the car will run badly. The valve lash and the timing belt are probably two things that likely have not been addressed on this vehicle and so are overdue.

teddy2828

a little update on my part. i replaced the fuel pressure regulator and then had the injectors cleaned at a local auto parts store.

the car runs soo much better now its not even funny. there are still some issues with it but i think they are unrelated to my post.

thank you fleabag and all the others who took time and looked at my problem.

fleabag

Well I'd like to thank you for taking the next step and posting a follow up!