Picked up an 850 Turbo about a month ago with 85k miles. Replaced the motor oil with Mobil 1, did a tranny flush, and ran Seafoam treatment. Also, changed the serpentine belt and installed a boost gauge.

Some service history:
60k mi.: Front o2 sensor
62k mi.: Ignition coil, fuel pressure regulator, dist. cap/rotor/wires
65k mi.: Timing belt, shift lever lockout switch, & coolant cap
67k mi.: Air mass sensor & turbo drain pipe seal
84k mi.: Both front CV axles & upper engine mount bushing

I cleared a long list of codes on the computer. The only one that keeps on coming back is 443 (Three Way Cat efficiency); it doesn't throw the check engine light. I can tell when the code is present when turbo boost will not go above 6psi. Once the computer is reset, I can boost at 9.6psi for a few days until the code comes back. Does it appear that the cat needs to be replaced?

Perhaps the results to the emissions tests may help:

Feb 2006
15 mph; 1725 rpm
%CO2 MEAS 14.8; %O2 MEAS .1
HC (PPM): MAX 84; AVG 21; MEAS 23
CO (%): MAX .49; AVG .06; MEAS .22
NO (PPM): MAX 692; AVG 150; MEAS 238

25 mph; 1717 rpm
%CO2 MEAS 14.8; %O2 MEAS .1
HC (PPM): MAX 49; AVG 13; MEAS 13
CO (%): MAX .46; AVG .05; MEAS .19
NO (PPM): MAX 711; AVG 136; MEAS 305

Jan 2005
15 mph; 1767 rpm
%CO2 MEAS 15.10; %O2 MEAS .11
HC (PPM): MAX 84; AVG 21; MEAS 59
CO (%): MAX .49; AVG .06; MEAS .21
NO (PPM): MAX 692; AVG 150; MEAS 359

25 mph; 1739 rpm
%CO2 MEAS 15.00; %O2 MEAS .07
HC (PPM): MAX 49; AVG 13; MEAS 33
CO (%): MAX .46; AVG .05; MEAS .20
NO (PPM): MAX 711; AVG 136; MEAS 321

 

Could be time for a new cat.

Also make sure the Rear O2 is working normally.

Is the car missfiring at all?

 

I had front O2 sensor tripping CEL a few times -I would clear the code (so the car does not run in retarded ignition mode), and it would come back after a few days. After a while, it gave "inefficient cat" code -changed the sensor, and no more problems.

PS
Seems too much service for the mileage- front O2 at 60 K miles? Both axels?
What year is your 850?

Also, some reported getting wrong replacement O2 sensor (from Autozone, etc) -was your O2 OEM replacement or not?

 

Tech: The only time it misfired on me was when I installed the wrong model spark plugs that Autohauz shipped. Other than that, besides have no cold/high idle speed, everything has been running smooth.

Yurionel: 1995; most services were done by an independent shop. I believe that oem parts were used. Looks like only the CV boots were replaced and not both axles. Front o2 sensor ($180) was replaced in June '03; codes 443 and 435 (front o2 sensor slow response) were tripped. I've cleared the codes and nothing else comes up now except for 443.

 

Usually that code will come up with a missfire code of something that makes the computer make the car run rich.

 

did it pass inspection? If not, I believe, aftermarket cat (direct fit) is about$200-250.00

 

Yes, the car passed the emissions test.

I've bolded the numbers in my initial post of the measured readings from the car. Numbers that are below the MAX are passing.