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Discussion Starter #1
1997 Saab 900 2.3 150000 miles
car has been running great!
On my way to a Thanksgiving gathering I filler'er up with Mid grade gas(89 octane). About 30 miles into the trip the engine starts, seems like miss fireing when I slow down for stop lights (very gerky). car is still running fine at higher RPM's ubove 30 MPH. So I finish my trip about 55 miles total. This morning I cleaned all plus wires & distributor cap. I did have an extra set of NGK plugs in the trunk so I put'em in.
Unpluded the battery to reset & when I restarted the engine, still have the same problem. Thinking about picking up a cap/ rotar and plug wires at Wallmart before going home just to see if that helps. Would like to use OEM but nothing open on Thanksgiving Day.
So anyway seems car has a very bad idle. But runs fine at higher RMS.
Any other ideas or suggestions would be great!
Happy Thanksgiving to all!
John
 

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Vacuum hose from the TB to the FPR, is the most obvious (and cheapest, at 50 cents per foot) guess. IAC valve, needing cleaning, if it only happens at idle, with foot off the gas.

Evap canister purge valve and associated hoses, are a possibility, lots has been posted about that.

Crankshaft position sensor, if it seems like the engine cuts out now and then, like a momentary stall. The sensor can start to fail at either low, or high RPM, depending on tyle of failure. Eventually this will produce a CEL, or the car will fail to start.

Good luck, and safe Holiday driving!
 

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If the cap and /or wires were really bad, the CEL would have been ablaze..These items do last a long time....I was thinking "IAC', but, I believe that Mr PMI is correct...
 

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Discussion Starter #4
Thanks!
Finally got to looking at it along w/ changing to snow tires.
Thats exactly what was wrong!
TB to the FPR hose was disconnected.
Thanks again!

p.s. Because of this awome site & the people associated with it.
My next vehicle will also be a Saab!! :)
 

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jbbcd said:
Thanks!
Finally got to looking at it along w/ changing to snow tires.
Thats exactly what was wrong!
TB to the FPR hose was disconnected.
Thanks again!

p.s. Because of this awome site & the people associated with it.
My next vehicle will also be a Saab!! :)
What do TB and FPR stand for?
Could this cause a slightly high idle? (about 1000 rpms)
 

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wingnut said:
What do TB and FPR stand for?
FPR = Fuel Pressure Regulator.
TB = Throttle Body.

The throttle body is cast aluminum, with a spring loaded throttle arm, and a throttle position sensor (potentiometer). On the 2.3L n/a engine the crankcase vent line leads directly from the valve cover to the TB. A 4-mm inside diameter rubber vacuum line leads from the TB to the FPR, which is mounted on the driver LH side of the fuel rail.

The vacuum lines run in areas subject to heat. The FPR vacuum line is mostly hidden. It dries out and cracks or breaks frequently, or just slips off the nipple at the TB. Then the FPR can't regulate fuel pressure properly.

Although the fuel pressure is nominally 3 Bar, it is regulated to be 3 bar above the manifold pressure via the vacuum line. If the line breaks, the fuel pressure will be too high. Although the ECM can compensate for that partly, especially on the n/a engine, on the turbo it also causes low fuel pressure during boost, and the A/F mix leans out to the point of causing a CEL and an engine running lean fault.

wingnut said:
Could this cause a slightly high idle? (about 1000 rpms)
It could, but the most common symptom on the n/a engine would be rough idle.

My car idles at 1000 rpm also, even with a clean IAC (idle air control valve), and good vacuum lines. I have been told that the ECU has to be recalibrated to the TPS (throttle position sensor) once or twice in the life of the car to fix that. That can be done by a mechanic with the right tools for about 50 bucks.

Replacing the vacuum hoses and cleaning the gunk out of the IAC valve and throttle body is a good idea every few years, although not as critical on the 2.3L n/a as it is on the turbo, because the turbo usually has much more oil in the air intake.

(bit long, sorry)
 
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