I've got this same problem…had a spill on the keyboard of the MacBook Pro (A1226, late 2007), couldn't be helped. All was fine afterwards, at first…then, as the day wore on and the keyboard backlight came on, I saw the lower left keys (SHIFT-FN-CONTROL-OPTION-COMMAND) were not lit as brightly as the rest of the keys--or at all. So I set about to fix it. I disaseembled the MBP, took apart the keyboard and cleaned the several layers of thin plastic that make up that assembly.
I reassembled everything--the keyboard was now lit properly, but that's when the fans started running at 6000rpm each, NOT right after the spill as one might expect. And, after installing and running the SMC Fan Control app, I saw that there wasn't an overheating issue.
I did the SMC Reset, Zapped The PRAM...it didn't matter.
After some effort I was able to run a copy of the AHT CD (even though I had the original install disks for Tiger). My MBP has Mountain Lion installed, and it refused to allow a boot into the Tiger Install CD (which is the OS that shipped with this computer). When I got all that corrected I received error code 4SNS/1/40000000:TsOP -128 000. From what I've read, it's the Palm Rest Sensor.
Okay, now this is where my sense of logic kicks in. Previous accounts had held (http://www.henrycipolla.com/blog/2011/05/macbook-pro-fix-4sns140000000-tsop-by-replacing-palm-rest-sensor-fixes-fan-constantly-at-100/) that it was the connector that attaches the keyboard assembly to the logic board. The author of the link says that he accidentally tore off some of the foam rubber that forms the top of that connector, while removing the Kevnar (yellowish) tape…and when he replaced the sensor (by replacing the underneath keyboard ribbon assembly), he found that it fixed the problem.
The problem with this diagnosis--and what I can't get my mind around here--is that I ALSO TORE THE TOP OFF THE "PALM REST SENSOR" of my MBP---SIX MONTHS AGO! I was careful to replace it back on the keyboard connector and tape it back down…and I had no problems.
I've purchased a new Ribbon Connector for the MBP "just in case"--and while I await its arrival in a couple of days, I was still unconvinced that was the source of the problem. So, I kept looking on the Internet…and found my way here.
So, there might be some merit to what 2Lazy says…I only wish he could say it a little better. Meaning absolutely no disrespect, as none of us is perfect…I read and re-read his unpolished response several times…and as I thought he might be on to something (and I obviously also haven't found the answer I'm looking for), I decided to post what I've found on here.
I'll examine the sensors as he describes, and when the keyboard ribbon assembly arrives I'll install it, and while I've got the MBP apart I'll take a look at that sensor …and I'll post when I've found on here.