Check engine light codes

code p0443 refers to EVAP canister purge valve--circuit malfunction===causes --wiring---EVAP canister purge valve--ECM

code p0451 refers to EVAP pressure sensor --range/performance problem===causes --EVAP pressure sensor

code p0135 refers to heated oxygen sensor(HO2S) 1 bank 1 heater control --circuit malfunction===causes --fuse--wiring--HO2S ---ecm

basically the HO2S sensor is not stable and altering the air/fuel mixture settings for the ECM and this is not being helped by a faulty EVAP purge valve and pressure sensor.

Check plugs leads , compression , Check petrol pump , And filters .

throttle has a lot of carbon build up need cleaning. if check engine light flashing code scan for code.but more likely could have clogged air filter.idle air control passage clogged dirty.check make sure throttle body linkage not binding sticking.

scan computer for codes auto zone does it for free

Do you have a check engine light? If so have Autozone tell you what engine code is ( free). Sounds like could be cranck shaft position sensor. Symptoms sound just like what ours was doing before we replaced sensor.

hey if necessary repairs were done and light stays on, chances are it is registering a "hard-code" that will have to be erased by scanner only

If you are getting a CEL (Check Engine Light) then figure out the code. This is an OBD-I engine so you need to connect the appropriate test connector and count the blinking lights. (Google Subaru OBD-1 codes).
Now as for your problem. Most common cause is the MAF (mass air flow sensor). The square box on the air intake. Try tapping it with a screw driver, the connect inside is joined only with solder and years of stress can crack the solder joint. If your engine stalls whenever you tap it, get a new one or rip off the cover and resolder the connect. Also check the IAC (Idle Air Control solenoid).

the idle air control valve is responsible for engine idle.
this is a common failure on ford's. but I don't think yours is bad because it does idle high befor it dies.
you stated you had codes p0171 and p0174 these are lean codes for bank one and two, you said you found a vacuum leak and repaired it, the vacuum leak was mostly likely the cause of the lean codes, however the pcm has calibrated the fueling stategy for this lean mixture, what you need to do is erase the KAM "keep alive memory" this is done by unhooking the negative battery cable for 60 seconds, this is the only way to erase the KAM the $6000.00 machine I use wont even do it.

once the KAM is clean the computer will go into a relearn state and all operating values will be adjusted for the vehicles current condition, during this relearn session the vehicle may have some driveability issues (low or high idle, stalling, poor fuel economy) the relearn should complete within 10 minutes of idling and then 10 minutes of driving.

good luck and keep me updated

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you probably need to check the butterfly. its the compinent that controls how much air goes into the engine if it is weared than in idle state air leaks into the engine sometime more sometimes less and cause fluctuations in rpm

secondly there is a rpm switch which controls the rpm you can replace that switch and check

You will need to check the Mass airflow sensor and the Idle position sensor.