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Message: <blockquote data-quote="EFN" data-source="post: 327241" data-attributes="member: 1416">As most of us have already known, 4A-GE 20V specially ST are notoriously easy to experience pre-ignition problems or more known as knocking/pinging - specially when the AC is on.One of the reasons is that 20V are designed to run on Octane Level 100 - so the system are optimized to run Advanced Ignition Timing. But in Malaysia, with RON97 and sweltering hot operating condition, Pre-Ignition are bound to happen more frequently.Other cause for Knocking/Pinging are Lean Condition due to the following factors:- Injectors clogged- Fuel Filter clogged- Fuel Pump weak- Fuel Pressure Regulator weak- Vacuum leaksAnd I found another one cause that I have overlooked for a very long time -PCV Valve slightly leak.- Yes, after troubleshooting my 20V fuelling gadgets, I have decided that none of them are the real contributor to my engine's knocking problem. So I began looking elsewhere and just today I decided to experiment with the PCV Valve which has been "senget" for a very long time and I never bothered to fix it up before. The Oil Seal surrounding the PCV Valve were somewhat worn out (13 years old engine - what to expect huh) and this has forced the valve to lean out exposing a very tiny bit of gap which might have allowed some air to seep into it. Fixing it up is easy, just take out the whole PCV Valve and wrap a healthy amount of Plumbing Tape around the lower socket and snug them back in. Check that the PCV hose itself does not have any leak and reconnect them all. Upon testing out my car, i immediately noticed the difference as my 20V does not knock that easily again when the AC is on, and it took me only 15 minutes to fix the problem! - should have done this long-long time ago.So you guys 20V owners out there, go ahead check your PCV Valve, if it is a bit senget and start to expose a tiny bit of socket, better get them fixed.Hope this helps.</blockquote>