dlx111

Car is 95 civic stock d15b7 220k miles. Been getting rough idle when engines warmed up or even when its just warm outside, and also rough "idle" when clutch is depressed and approaching stop. When coasting still in gear no issues and under throttle driving around no issues at all. Starts off mild then gets pretty rough and bad feels like cammed motor almost.

Replaced nearly every vacuum line i know of thought it was vacuum related. New injectors and FPR, new MAP sensor, TPS is good, IACV cleaned and working, PCV cleaned and replaced, intake manifold and throttle body all cleaned, new head on motor and new gaskets all over. Timing is correct, fuel pump is priming and car starts mostly no issues. Fuel filter replaced. Fuel pump still stock as is main relay but pump primes and starts so dont think its that.

Evap system was disconnected thought the purge valve was creating a vacuum leak but new lines on it and valve is disconnected. No catalytic converter. Havent replaced o2 sensor thinking it could be that but symptoms dont sound like whats goingg on.

anyone got any ideas?
car gets 34mpg consistently so not like its running really "bad" but when im stopped at lights sounds and feels like its gonna stall out it idles so bad

mk378

I assume the CEL is not on and you have tested and found no codes.

Test TPS with a voltmeter, very important to have the 0.4 volts with throttle closed so the ECU knows it should idle.

Valves that are too tight a clearance will cause misfiring at idle, so check the valve adjustment.

Vacuum leaks generally will make the Civic's MAP controlled engine idle faster (pull one of the hoses off and try it). This is different from most newer cars which are MAF controlled, on those a vacuum leak causes a slower rougher idle and/or stalling out. So I don't think it is a vacuum leak.

Idle speed should be set up by unplugging the IACV while warmed up and idling. This should instantly throw a code 14, which proves the CEL is working but otherwise you can ignore it. The speed should slow down. Adjust the air bypass screw, the big flat head screw on the top of the throttle body, for about 450 rpm i.e. barely running. Then plug the IACV back in and a normal idle should resume. DO NOT adjust the little screw that stops the throttle plate. Also make sure the throttle cable is slack and the plate all the way closed when no one is pressing the gas pedal.

dlx111

yeah no CELs checked it its clear. Previously the car was not running at all the dealer ended up figuring out it was the injectors and FPR so it ran after that, and they said they adjusted the idle speed too so I assume they followed the correct method. The thing is though it idles fine when its cold so wouldn't the set idle speed cause it to idle bad no matter what temp?

mk378

No. When cold, the valves are looser. Thus you often hear valve noise upon startup, but you're less likely to lose compression through a tight valve. Also when cold the ECU runs a different logic which has a priority to keep the engine running. After it warms up the ECU goes to "closed loop" mode which has priorities of mpg and low emissions, this tends to bring out runnability problems.

So go through the troubleshooting drill over again. After replacing so many parts with no results, it is best to forget everything that may or may not have been done before and check over the whole car like you've never seen it before.

dlx111

Adjusted idle, theottle cable was slack, seemed to make a little bit of difference but today after coming off the highway into city traffic idle went back. When getting on brakes coming to stop clutch in i can feel it start to bog and then at stop rough idle resumes.

Didnt adjust valves yet but i will say my old head the valves were adjusted and it was still doing this, came to find out though one valve was a little burned up. But havent adjusted valves on new head yet.

Doest the o2 sensor read at idle and low load? I had a subaru and i know the o2 sensor only accurately read AFR at idle and low rpm then a wideband downstream catches more. Just been thinking about that

dlx111

Got a CEL yesterday for the first time ever, got code 6 and code 14. i know 14 for the IACV is probably from me messing with it adjusting idle speed so im assuming maybe connector is just loose, but Coolant temp is an odd one going to check connection there doubt it has anything to do with the misfiring though

Megalodong

Test for possible lean condition:
Disconnect air intake from throttle body and at idle spray some throttle body cleaner spray into TB. Listen for engine rpms to raise for a short period of time and if rpms raise could indicate a lean condition.
Do the same test at a steady (as possible) 2500 rpms and see if rpms raise.
Pull spark plugs and inspect for fouling...lean fuel shows as dry, white buildup.
Have a freeze frame/live data scanner?

dlx111

I dont. I havent checked my spark plugs recently im going to tomorrow though because last time i did which was a few months ago when I was still having the idle issue they looked a little black like rich. Im going to test IACV wiring and ECT wiring this weekend too because i know the IACV is working but now the connector is being stupid, this morning car wouldnt start had to play with the IACV connection and then it was fine. On the way to work today too car felt great under load, idk if the fuel had corrected itself or what but felt quicker under throttle.

dlx111

Replaced ECT and o2 sensor, misfires and roughness seems to have resolved. No more CELs either.

Megalodong

Nice work. Thanks for the follow-up.