93wrx, K&N, TSL centre section & backbox - ongoing problems. Main problem is that I can go for a run and car will boost to 0.8 bar, perhaps over twenty non-dual carriageway miles or so, then will only boost to 0.5. Sometimes it will boost up again and sometimes not. Did also have CEL codes 23 and 24 - MAF sensor and Idle Air Solenoid. Checked MAF sensor readings with multimeter (OK), took it off, looked at it and put it back on - no more code 23. Same with idle air solenoid, took top off - which was magnetised - twiddled spindle thing underneath (which felt quite free)and replaced. Cleaned Boost control solenoid with carb cleaner, worked ok in test mode. Same boost problem and CEL code 24 appearing. When the CEL illuminates it doesn't coincide with lack of boost. Fitted new spark plugs - I'll be quicker next time - boost problem persists but no CEL. Sorry, long-winded, but here are my queries: 1)If it's checked using a select monitor, can problems be diagnosed that may not even display in the CEL system? 2) Should I suspect the ECU, if so what do I do to establish if its faulty? 3) What should I try next?

Try swopping the "MAF" sensor if you can, as have found these to "check out" on the bench, but when under engine running conditions, have failed, surely someone local to yourself has a similar motor, its worth a try first and may cure it.

Lots of water can do what you have descirbed, fools MAF sensor, which screws up idle, and the valve can't compensate.

Chugging along on idle, keeping the revs down can throw a ISCV CEL code too, as it can't get the idle revs correct.

The older MAFs are usually very robust. ONLY error I have ever seen was mechanical, under the square lid, that is siliconed in place, is a sheet metal EMI shield, which was dented and shorting something. I removed the lid (cut round silicone first) des soldered the shield and flattened it, resoldered, resiliconed lid, good as new.

Paul

Meant to add, the reason the fault was diagnosed, is the car could be made to stumble on idle by squeezing the maf sensor, indicating some connection inside was suspect.

Paul

Had same problem on my 93 wrx first check what level the oil in the engine is should be half way not on the full mark otherwise you will just keep contaminating the solenoid valve next clean all the solenoid pipe work to remove any particles of oil the connect the test plugs under the dash and the solenoid will start clicking now spray in cleaning fluid this will thoroughly clean solenoid out i think it is the green plugs you connect i may be wrong if you do a search then you can see.I had exactly the same problem though car would run 1.1 bar boost for a few days and then all of a sudden only 0.5 bar cleaning the solenoid out on cycle mode must have removed the oil that was making it stick as i have not had any problems since.

Mark