Full history - car has been in about 7 times for a P030X - usually cylinder 2. They've replaced the coils, plugs, etc. WHen they replaced the plugs at 30-ish thousand miles, they were sooty. Since then, the misfire has come and gone. It only surfaces as a MIL. The car now has about 46,500 miles.

Anyway, I was ready to list the car on ebay, so I washed the engine. And promptly took out the knock sensor. Replaced the knock sensor (went ahead and replaced the plugs again), and it ran fine. But, the car is rarely driven anymore, and now it seems to be causing two problems. One is a P1540 code (air bypass valve circuit) that is transparent except for the MIL. The other one is the TCS intermittently malfunctions. So, two problems:

P1540 - is this the idle air control valve (aka idle speed control valve, aka IAC, or ISC), or is this the recirculating valve from the blower to the low pressure side? I initially think that it is an IAC, as the recirc valve is entirely vacuum operated. But, IAC should throw a 1504 code.

TCS. This is a bigger issue. The vehicle slows, and has a very hard time accelerating. Then it has a hard time shifting. I can reset the malfuntion by keying off, then on. I can do this even in neutral while the vehilce is rolling. Any ideas?

Other notes. I'm a pretty competent mechanic, and an engineer for Ford. But unfortunately, I don't have access to a lot of the Mazda specific stuff. Any help anyone here can give me would be greatly appreciated.

 

PLUGGED CATALYTIC CONVERTER?

WHEN THE COILS GO AND THE PLUGS LOOK "BURNT"...USUALLY THE O2 SENSOR AND CATALYTIC CONVERTER ARE ALSO BURNT

 

P1540 is the ABV solenoid, here is a quote from another forum I belong to;

"OK I have the same problem and have traced it back to a faulty ABV solenoid valve (vacuum) which is on the the back of the engine with two other valves and a small air filter. It is the valve on the right side as your looking at it. If you have a multimeter take a reading across the posts should be 22-26 ohms, if higher (mine is 138 ohms) then you have to replace it. If it cannot read then it is also finished, dealer only part , but only $62 CAN. It is not a normally stocked item so they, of course, have to order it and make you wait! I have the 12V going to the valve, but not enough to move it becasue of the high resistance. This acts as a block in the vacuum system, and therefore reaks havoc on everything. " P1540 Troubles

Hope this helps. It took me a long time after replacing the Supercharger(the seals blew), and the complete vacuum hose system to find this one solenoid!
But it gave lots of other codes too.