Mbtech

Hey all, purchased an 01 civic lx 5 speed sedan about 4 months ago for my commute to work and wow has it been a money saver! The only issue Ive had with it is it has been plagued with a rough/almost stalling idle that gets worse when the vehicle is warmed up to operating temp or with a/c or any type of load on the engine. The main issue I have is when coming to a stop the engine drops to about 200rpms then revs up to about 1000rpms and then settles at about 600 rpms but not always, sometimes it just barely makes it to 400 rpms and just stays there and has a terribly rough idle, hood shaking, dash shaking, door panels rattling. I began by searching forums including this one on what could be causing the idle problem and did not find anything that seemed to be similar to my situation especially having no fault codes. To date here is what I have found/tried/tested:

Spark plug tube seals leaking, replaced seals and valve cover gasket and installed new ngk single platinum spark plugs and installed new honda coil on plugs. Did not make any difference. Also checked valve adjustment and all were right in the middle of spec. per my haynes manual and alldata

Replaced throttle body with new throttle body assembly from Honda and performed idle relearn. Did not help any.

Had a fault set for thermostat performance randomly and thought surely this would fix my problem, replaced faulty coolant temp sensor and performed idle relearn, Had no effect besides no more cel/fault.

Performed cylinder balance test and found no dead/weak cylinders.

Checked compression dry and all 4 cylinders at 135psi wet all at 150 psi ***is this ok? Found different specs between haynes manual, online, alldata etc.***

Replaced all 4 engine mounts with honda engine mounts due to being worn/torn.

Replaced fuel pump because it was cheap and felt like throwing a part at it lol Had no effect.

Installed new gates timing belt, water pump, and tensioner pulley. Replaced oil pan gasket and crank seal due to oil leak. Timing belt etc. Had no effect.

Tried driving around with upstream o2 sensor unplugged because there were a few people that had a bad upstream o2 and that seemed to work to prove it was the sensor causing the issue, had no effect. Also checked output voltage using my scan tool and it is sweeping correctly anyways, just figured it was worth a shot.

Removed upstream 02 sensor entirely to see if vehicle ran any better which may point to a clogged up cat, had no effect.

Checked for vacuum leaks using smoke machine and spray test with brake cleaner while monitoring o2 data and did not find any evidence of a vacuum leak.

Sorry for the long post but Im about at the end of my rope on this one, I have no idea what else to check.I appreciate any and all insight.

Aug 14, 2016#1

Wankenstein

Did you try cleaning the idle air control valve?

Mbtech

I did try that but it didn't seem to help any so I ordered a new Honda throttle body. It came with a new tps and idle air control valve and did the idle learn procedure and it didn't help any at all.

Wankenstein

There's a couple no cost things you can do that may help:
1) Elevate front end and bleed air from coolant
2) Clean and retighten all chassis and engine grounds.

You've ruled out a lot so it may be leaning to a timing issue.
Worn primary o2 or A/F sensor that is not throwing a code is a possibilty

Mbtech

Ok I'll give those a shot thanks, I checked the timing before I did the timing belt etc. and it was right on according to my haynes manual, and when I put it all back together I did a double take to make sure it was all lined up correctly. I replaced the upstream o2 a couple days ago with a denso and I haven't noticed any improvement.

Mbtech

Update on this: found that the head gasket was leaking slightly between cylinder 4 combustion chamber and cooling jacket. Replaced the head gasket and re tested it and no more leak, however still having the same rough idle issue.