I got 3 codes, p0303 cylinder 5 misfire, p0343 camshaft position sensor, and p0139 02 circuit slow response, mechanic saying to swap engine??!

 

Swap mechanics.

Ah perhaps I better add something more subtantial than a smart aleck (but I think in some ways appropriate) comment...

The engine may be toast but the error codes do not point to that.

Misfires and the other errors you listed can arise form a number of causes. Not all require an engine be replaced. Without knowing the history of the car plugs and coils can certainly be a contributor as far as misfires go.

P0139 is Aging of oxygen sensor behidnd 3-way converter bank #1 (cylinders 1-3). Briefly the recommendation is to clear the code (which clears all codes) and road test the car. If the P0139 error returns replace the indicated sensor. My advice would be to replace both the "bad" sensor and its counter part on the other bank and if the car's miles are "high" replace all 4 sensors. (When a sensor on my 2003 Turbo started tripping an error I had all 4 sensors replaced. They had lasted 132K miles and I felt I got my money's worth. Might add the engine ran a bit better after new sensors, too.)

New sensors might (might...) help with the misfires.

P0343 is Camshaft Position Sensor 1 – Above Limit.

Potential causes:
– Short circuit to B+
Check the connector/wiring.
Check signal wire from DME control module, pin III/20, to CMP sensor for short circuit to B+.
1. Connect special tool 9637 to wiring harness (DME control module connector).
2. Remove connector of CMP sensor.
3. Connect voltmeter to special tool 9637, pin III/20, and ground.
Switch on the ignition.
Display: 0 V
If battery voltage is displayed, check wiring harness for chafing and pinching damage.

The above shows there is a set of steps to go through that help one make a proper diagnosis. Some knowledge of the engine is needed along with the special tool 9637 (kind of a glorified break out box for Porsches).

There's more - and I can supply you with it if you want -- but the point is this is most likely bad sensor or possibly a connector/wiring problem none of which require an engine swap out to address.

 

get a second opinion. if you are anywhere near Orange County Ca try Bbi Autosport.