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Old 11-25-2011, 01:59 PM   #11 (permalink)
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Long post. If I wrote someting incorrect, straighten me please.

For quick info go to Chapter 2.

Chapter 1.

Some time ago I had iddle issue. 93' Civic VX, 250000km.
- cleaned EACV
- adjusted iddle
but the real couse was Purge Control Selenoid Valve (PCS) vacuum pipe was cut a bit, PCS had oslo some small crack causing air leak. Constant vacum control valve (CVC) had some crack hidden close to manifold vacuum pipe (someone had to pull the pipe causing crack or someting).

After some time the iddle problems came back to me .
I started digging forums again and I've found a lot of useful info and long stories about iddle issues. Every case looks a bit different so I'm pretty far away from saying "check this and that, it will fix you problem" but I'd like to share some thoughts and observations.

Temp went down from 15'C to 2'C (arround -5'C at night) during last weeks. After starting 1500rpm's - acceptable, no fluctuations. Once it got warm iddle went down to about 600rpm's. When I stopped on lights the iddle fluctuations appear (from arround 400rpm to 1100rpm) . I always try to think what has changed:
-maybe some valves got dirty too much to work as before
-maybe some sensor died
-outside temp. went down

Chapter 2.

Again I've checked all the piping for vacuum leaks - no leaks . I looked at vacuum diagrams for long time, I even created some kind of Ishikawa diagram . I knew my Electronic Air Control Valve (EACV or EAC) called sometimes Idle Air Control Valve (IACV or IAC) is clean, PCS and CVC is repaired, i don't have vacuum leaks for this part of the system. I went to other parts of the VX system. I've read about PCV valve which is located deep under intake manifold. I took a look (it's not easy to find it for the first time) and reach it with pliers. PCV was clogged (which seems like common problem) but I noticed PCV rubber is very hard (can't blame 93' car) and there were oil leakages arround the PCV hole. I've cleaned PCV and decided to swap hollow elbow with PCV, put new long pipe from elbow to PCV. Hollow elbow rubber was also hard so I had to use some thin sticky rubber tape to seal it. The best way would be to change all rubber parts for sure (that's the plan). Last thing was iddle adjustment (standard well known precedure: engine on, unplug EACV, make short circuit on diagnostic plug, adjust screw on TB (set iddle - fot VX 420 +/-50 rpm), turn the engine off, unplug short circuit on diagnostic plug, plug in EACV, take out back-up fuse for a minute, wait to cool down, start engine, wait until the radiator fan starts, take a ride).

So far it works but what makes me think is the rubber parts and vacuum leaks. They are also crucial for the iddle issues and pretty "cheap" and easy to verify at the first place. I could change plugs, wiring, check grounding, clean TB, change ECU, try to adjust iddle etc. without any success.

Chapter 3.

I totaly agree that sensors fail, good ground is crucial for all electrical devices, welds are important, vibrations can wear down the wiring insulation.
Although I think at the beginning it's worth to remember what is the sytem based on - air, electrical signals, rubber, plastic, metal etc. As we all know most of the holes made in engines (e.g. aluminum alloy) are getting bigger while hot. Rubber could get more flexible but it's not expanding like aluminum alloy.

Everytime I'm looking for causes of failure I try:
- start from basic things (like is there vacuum, power etc. at all)
- to go back (step by step),
- think what has changed,
- when exactly it started,
- what was the exact situation,
- who was fixing IT (who? how? where? when? with what?)
- how all of this could influcence my problem

Unfortunately lots of failures appear as resultant of different small failures and that's why they are so hard to solve. The only way is to trace them separately and try to eliminate them each after another.

The End - sorry for long post.
I'm also sorry if I sound like I knew more than I know

Thank you to all who shares the knowledge - I would be in dark forest now without YOU!
I wish you all patience and time.

Last edited by cnc; 11-26-2011 at 03:13 PM..
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