P0172........
 

been searching for a while, on my old 2000 4runner 5spd 4x4 supercharged with 7th inj, it just started to run rough here & there, seemed like it was mostly after it was warmed up, now idles low & chuggy, and surgy when accelerating & threw a p0172 - system to rich. From what ive found... the culprits for po172 seem to be:

MAF - already replaced dealer item
Front 02 sensor - Replaced dealer item
Injector leak/blockage
Engine coolant temp sensor
Fuel Pressure
Gas leakage on exhaust system
Heated oxygen sensor - bank 1 sensor 1
Ignition system

So thought it might be a simple maf & 02 sensor, so i switched em out for dealer new ones for my vin#, left batt disconnected for an hour, hooked it up and drove for 50 miles....still same prob. I had my injectors cleaned by witchhunter about a year or so ago, and ive got the walbro 255 fuel pump in the tank due to the blower. Ive checked all the wiring to the pnp harness for the 7th inj, even unplugged it and just used the stock ecu, but still same prob. Plugs are clean, in fact new IK22's as of a month ago.
Ive never heard of the FPR (fuel pressure regulator) go bad on these motors, but how do i check? Would the coolant temp sensor really make it run rich?, cant see how. Any input is appreciated. thx.

When coolant temp sensor fails open (not uncommon), ECU thinks motor is cold when it's hot, thus going into open loop and forcing a rich mixture. Running better at start-up tends to say this IS your problem.

On the 3.0, the FPR has I think 2 hoses, one return line and one vacuum line that goes into the intake. Find that hose that goes to the intake and pull it off the FPR and wait to see if fuel drips out. IF SO, your FPR is bad, causing your engine to flood. . Just remember to pull of the correct hose :)

sounds reasonable, where is the coolant temp sensor located?

http://tacoma.site40.net/4Runner_96-.../ects/comp.pdf

http://tacoma.site40.net/4Runner_96-.../ects/insp.pdf

Awesome, thx. Will break it down this weekend.

Before doing that....what I would do is get your hands on something that can live scan...Scanguage II or Android with Torque (what I have), whatever. It's a good investment even if you have to buy. Then watch your reported engine temp and closed/open loop status as car warms up. You should be able to tell pretty easily if the ECT is whacko enough to throw off the ECU into open loop. It's a big job to do just on a guess. If this is the problem, it's not off by a few degrees, it's off by a LOT.

well i put a new engine coolant temp sensor - the one for the EFI as pictured above, and no difference after battery reset and driving 50 miles. Maybe i can describe the prob better.
Now as i accelerate gently/normally (not wot) it chuggs then drives normal. It still feel like its fighting open/closed loop. Im completly stumped on this, and i usually figire things out pretty easily. Unless i give in and take it to the stealership...im at a loss & i dont have access to any live scan gauge.