9-5 idles rough & smokes a little after half hour of driving
I just purchased a 2003 Saab 9-5 (2.3L) cheap, but had to buy it sight unseen because of its location. The Previous Owner (PO) said it started fine but then idled low and rough, and sometimes would not restart easily after warming up. He said it always started easily when cold. Prior to purchase, I had a mechanic go out and check the compression, and he reported it at 180 on all 4 cylinders. He listened to it run, and said it sounded great mechanically. He said he had to run it about 45 minutes (not driving, just running) before it started running rough. Both the PO and mechanic reported the check engine light to be on. Neither the PO nor the mechanic had the means to check the codes.
On that basis, I suspected a crankshaft position sensor going bad when hot, or other electrical problem. I am new to Saabs, but a competent diagnostician and mechanic, and it was so cheap I thought I'd take a chance. (I understand the risk I was taking was pretty significant, but again, it was so cheap there really wasn't much downside.)
The car has 86k miles, but the PO has said the engine was swapped out with a used engine in the past 6 months, and not driven much since. He thinks the turbo was rebuilt, but is not sure. The mileage of the used engine is unknown. It is also not certain whether the turbo on it is from the original engine or came with the used engine. I did get a spare turbo with the car, but it is toast. I'm not sure I'm getting the whole story from the PO.
The car arrived, and I've spent only a few hours on it, changing engine oil (Mobil 1 0w40) & filter (Bosch), and checking the car out. It is in surprisingly good condition overall, and at first I thought the problem must be intermittent, because it drove so good. I've started it several times, and have let it idle for up to 20 minutes. I drove it for 20 minutes when warming it to change the oil, and afterward it drove awesome for about 30 minutes. I saw nothing unusual. Boost builds just as expected, runs all the way to the right edge of yellow under load, and doesn't go into the red. (I didn't drive it hard or run the revs very high.)
However, after about a half hour of mild driving (some stop and go, some 50mph roads), it started idling rough, and I had to keep my toe in the throttle a little to keep it running when stopped at a light. Exactly as the PO had described. I pulled into a parking lot, and noticed a bit of white smoke drifting with the wind. I rolled down the window and asked a bystander if the car was smoking, and they responded yes. Back at the shop, it was idling rough but kept running in Park, and I got out and looked at the tailpipe. Sure enough, a little white smoke that smells like burning Mobil 1. (I know what burning Mobil 1 smells like from having spilled some on the exhaust manifold of my Chevy truck. :)) This perplexed me, because the Saab had not smoked before, nor had the mechanic or PO mentioned any smoke. After letting the car sit a while and cool down, when I restarted there was not the slightest hint of smoke, nor did the exhaust have any burning Mobil 1 smell.
This leads me to believe that the turbo is leaking oil past the bearing seals. Perhaps leaking on the exhaust side, and the rough idle and check engine light are the result of the oxygen sensor being inundated with hydrocarbons. Or perhaps leaking on the intake side, and the rough running and engine light are from burning oil in combustion. (although this seems unlikely because of the lack of smoke on cool start-up.) I suspect the turbo, and not rings or valve guides, due to the complete absence of smoke until well-warmed, along with the compression report given by the mechanic.
So, what I'm asking here is:
a) Does my theory of bad turbo seals sound likely?
b) Are there other scenarios that would fit these symptoms?
c) Any other feedback or input?
d) Suggestions, please! :-)
Thanks for any input you may have!
