2001 Legacy cold start stalling and 02 CEL questions

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Car is a 2001 Legacy 5MT with 127k on the 2.5 engine swapped in just before the PO bought it, 233k on the car. What it does is stall when cold the first time or two I come to a stop. Just drops like a stone past where it should recover and idle. Once warming up, it drops a little past idle and recovers, once warm it idles like a kitten.

I've looked around on the web and it appears there are some recommendations for this problem, such as temp sensor, plugs and wires,
fuel system cleaner, fuel filter. I've changed the fuel filter, added some Lucas fuel system cleaner, and ordered NGK plugs and Denso wires and a temp sensor.  Awaiting delivery from Rock Auto.

My only remaining question is how sensitive the Subaru fuel injection system is to vacuum? On a Bosch (early Volvo for example) FI system, it is extremely sensitive to vacuum and this could be a small crack in a vacuum line that closes when it gets warm. Any time I bought a Bosch FI car, I always replaced all the vacuum lines on general principles.

 

I should mention that the CEL is on for the 02 sensors, details on the CEL are below.

 

The CEL's have been on since the PO bought the car (maybe since the engine was swapped in, can't say), he had them scanned and they were related to the 02 sensors. I replaced both with the correct Denso units for a manual trans 01 (front is called an air/fuel on the box, rear is called an 02 on the box).

The CELs (my generic OBDII scanner shows 2x P1133/front 02 sensor heater from what I can find on the web and 2x P0141 bank 1 sensor 2 sensor heater malfunction, I assume this is the rear?) come on immediately as soon as I start the car after I clear them. Key to on, CEL off - key to start, CEL on. As soon as the car starts, it appears that the codes are set.

A local Subaru guy mentioned that there were problems or a TSB for ECU problems related to 02 sensors or a possibility that the ECU may be behind the problems? I searched the web and can't find any official TSB's for ECU's for this year of Legacy. Does anyone have any knowledge of this TSB? Is it possible that the ECU is responsible for the problems? The Subaru guy checked the wiring when doing the TB service and did not find anything wrong. I just find it odd that both of the codes show up immediately as soon as the car is started, that doesn't sound like wiring to me.

 

I couldn't find any fuses or relays for the 02 circuit that wouldn't affect something else?

 

Thanks for any comments/suggestions.

 

Interesting tidbit - I actually have two Legacy L wagons that are exactly the same colors inside and out, mine is a 2001 manual and my son's is a 2002 automatic.  Mine has a few more options but otherwise identical.  i was looking into the changes in 02 sensors between 2001 and 2002 and when comparing VIN's, I found that these cars were 189 apart on the assembly line (9 hours based on SIA web site).  The 2002 went to North Carolina, the 2001 stayed in Ohio, and both ended up in my driveway in late 2014. 

 

[Fairtax4me]

I don't remember if those have fuses for the O2 sensor heaters. Check the fuse box.

The codes setting immediately says the heaters may not be getting power, or the heater circuit could be shorted to ground. I would suspect a power problem since you have those codes for both front and rear sensors.

 

Plugs wires, basic tune-up is a good place to start.

Vacuum leaks do have an effect on these but a small leak sometimes isn't noticeable at all.

 

If that engine has the small idle air control valve on the side of the throttle body, remove it and clean the cone and the bore in the TB. A sticky IACV can cause it to stall.