I'm hoping this is not the case and that I did something wrong during the install. I'll wait a day or so before I take another look at her. If all else fails I'll be taking her to a local mechanic. Just not looking forward to being jerked around and it ends up being a loose ground wire while they charge me $$$$ to tell me it was the FPS. I'll post again when I have an update. Thanks.

08 GS 350 P1235 P0200 problem solved! You'd never guess how...
 

I had been trying to figure this OBD code (P1235) out for the last few weeks since my car originally stalled out on me. I bought a remanufactured Fuel Pressure sensor (part # 89458-30010) from eBay for $21 as it appears to be a common culprit. I installed the part and kept getting the same code (P1235) which I would erase and it would almost simultaneously return. The car would run for a couple minutes and then die which had me completely baffled. I try my best to handle most issues with my vehicle as I've heard many horror stories when it comes to dealing with Lexus for an older vehicle.

I scoured the remaining forums and came across a number of suggestions. I read that many re manufactured parts can be defective. It was also suggested to back track my work to ensure all wires and connections were in good condition. With that, I decided to bite the bullet and buy the OEM part (89459-30011) from an online retailer for about $250. I also backtracked my work to ensure everything was status quo. I even cleaned my MAF sensor, swapped out my PCV valve and cleaned my throttle body.

Once it arrived I installed the new Toyota FPS Part #89458-30011. Once installed the car would turn over and die after a couple minutes like it did with the reman part from ebay. I was getting the same code( P1235) every time. I would erase the code with my scan tool and it would come right back in seconds. I was almost convinced it was not my fuel pump as the car would still start faithfully and I could hear it engage.

I reviewed more posts with the same issue and came across one from 2015 by Irfan1994 on the IS forum. His post stated the Lexus dealer completed the following to fix his similar issue:

"PERFORMED DTC INSPECTION, FOUND DTCS P1235, P0200
PERFORMED VOLTAGE & OHM TESTS
FOUND LOOSE CONNECTION AT DIRECT FUEL INJECTION DRIVER
SECURED CONNECTION, CLEARED DTCS & ROAD TESTED."

I went and unbuttoned the front of the vehicle to take a look at the Direct Fuel Injector driver. I noticed the driver was a bit loose as I had replaced the water pump back in Dec 16'. I removed the Direct fuel injection driver from its place on the block while leaving its connectors intact. I found the ground connections and cleaned its bolts and connector rings with a wire brush (one right above the driver and one on the block). I buttoned everything back up and figured if this is not it I'd have to get her over to the dealer.

The car fired right up and the code (P1235) came back on. I cleared the code and waited for it to return in seconds like it had previously but it didn't. I waited another minute or so and no CEL and she kept running. Happy and a bit apprehensive I tapped the gas and watched the RPM's rise in amazement.

I then test drove her in our development and she purred like her old self. My baby is back from the dead after three weeks!

So after all that, it was a DAMN GROUND WIRE and CONNECTION that had become corroded!! Thanks to this forum I have successfully maintained my DIY status. I appreciate you Guys immensely. Cheers!

You have know Idea how good it felt to not see that CEL light staring me in the face! On top of that the FPS has been installed so another potential future issue has been averted. Thanks again Guys, Your the Best!!