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Vacuum Leaks and Poor Idling FAQ

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Generously maintained by William "Chip" Lamb (

While these are not guaranteed fixes, they are common trouble spots on older (or "Classic") 900s and some 9000s. Over a period of 10-20 years (can you believe that there are 20+ year old 900s out there??) rubber vacuum lines become brittle and/or swollen and can become so bad as to leave you stranded. Sometimes, EFI or turbo-related components can go bad and leave you stranded in Manhattan, Kansas. Here are some good things to look at:

up-to-1988 99s and 900s with 8 valve 2.0 litre engines: Big thing here can be a broken auxiliary air valve, which is the component between cyls #2 and #3 on a B motor (through 1980 99s and 900s with CIS injection) or on the left side of the cylinder head on an H motor car (1981 900s on). When cold, the internal thermostatic spring should be contracted and have the valve half-open, allowing extra air to supplement the 5th injector's extra fuel. Related thermoswitch can also keep fuel from coming out the cold start injector but failure here is less common. Warmup regulators (two small fuel lines running to and from it) can also go bad and not deliver more fuel to the injection block when cold.

1985 and later 900s and 9000s, poor cold starting: the Air Mass Meter, especially on LH 2.2 (1985-88 turbos, 86-87 S cars) equipped SAABs. Not much you can do here except adjust the screw as mentioned in the Adjusting Base Idle FAQ and check CO output or duty-cycle on the O2 sensor. Baseline setting for the LH 2.2 AMM is 380 ohms, measured between pins 3 and 6 of the connector on the meter. This is NOT a definitive setting but it can get you closer, every car's mixture requirements are different, just because the Bentley manual says 380 is the end-all, that's only partially correct. Now, if you've not had the AIC/IAC (air idle control) valve off and cleaned it in the last, oh, 10 years, it's probably time to get all the crud out. Pop it off, two lines and a 10mm bolt holding the clamp down, release the 2 or 3 pin electrical connector, and hit it with some good-quality carburettor or throttle body cleaner. On LH 2.4 cars you can work the little flap back and forth a little to work out the gunk. On LH 2.2 cars you cannot move the flap but tilt the valve upside down so that the insides are able to soak in the cleaner for a minute or so, toss it out, and clean out the insides as best you can with a LINT FREE RAG. If you've got a warm hunt this can be an instant cure. What, you ask, clean the throttle body too? Absolutely! Sometimes oil and carbon residue can collect near the throttle butterfly or on the throttle position sensor, so spray it out with the throttle plate open (same carb/TP cleaner) and use your lintfree rag again to wipe it clean. This is another warm idle hunting fix.

All 900s: The quickie-lube guys are famous for knocking off vacuum lines over by the oil filter, those little ones with the T fitting going to various locations. That can be a big leak as the feed for that is right over by the throttle body or just after it. Turbos, you have lines-a-plenty both small and large in more locations. Torn boots to the intercooler, turbo housing, throttle body and mass meter are common on high mileage cars. Also the little fitting in the plastic tube in front of the clutch cover can come loose, I saw a guy at the Keystone convention in 1999 who thought he needed a new AIC valve, this fitting was it. Oh yeah, don't forget those plastic fittings with the rubber grommets right there on the intake manifold, take really good care of those.

Here's a new one on me, applicable to all 900s, which I fixed tonight to the chagrin of my wife and prompted me finally to write this FAQ. Our "new" '86 SPG (900 turbo, LH 2.2) had a bad cold starting problem, where it would hunt when cold and stall out occasionally. I replaced the air mass meter with a known good one. No change. While driving the car yesterday and today, I noticed that with the climate control knob at the 6 o'clock position (OFF), that under boost air was coming through the vents. Remember that the flap controls for the cabin vents as well as the dash control are vacuum operated. As the car is a turbo, and in boost, you have pressure, not vacuum. To counteract this, SAAB put a check valve on the vacuum canister which provides the climate control switch with vacuum at all times, even with the engine off. This canister is on the right side inner fender area, and on a 16v requires moving the power steering fluid reservoir, the recirculator vacuum solenoid and perhaps (permanently?) a SAAB guard alarm horn. Sure enough, the built-in check valve on the canister was no good. I recently retired my '82 900T and it had a fine vent system, so out came its canister. Now there is very little air coming through the vents, perhaps just from the foam having rotted away somewhere within the dash and allowing a minute amount to come through. Best of all, the cold starting problem is no more.

9000s: We had a fun time in the parking lot of our hotel in, you guessed it, Manhattan, KS, en route out to the aforementioned owners convention with our stalling 9000. Turns out it wasn't a bad problem like a torn intake boot (each cylinder has a rubber boot right beneath the manifold, yikes!) but the line to the crankcase ventilation system from the intake manifold. I substituted (temporarily, mind you) a windshield washer hose for the interim. NOW - when you go out to buy that mile and a half of small vacuum line, DO NOT use windshield washer hose. That stuff swells like crazy when in contact with power steering fluid, oil, et.c., the stuff all 8v and 16v motors like to leak just enough to ruin your day. One of the local dealers used it to completely reline a customer's car. That customer came to me with a high idle a week later. Sure enough, his pristine engine bay had a bunch of washer hoses on it, and it was merely the operating temperature heat which caused them to swell, crack and fall off in a number of different spots. Needless to say he was not impressed with the dealer. But aside from those intake manifold boots, 9000 folk need to look at the same stuff the 900 folks do, those small vacuum lines (no, you don't have a vacuum distribution switch for the climate control, relax) and the other intake boots as found around turbo components, mass meter, intercooler, throttle body, et.c.

I'll end with my special Turbo supplement. You Turbo guys gotta remember, that boost pressure does weird things to hoses which are not clamped down tightly or are really worn out. Towing a '66 96 over the West Virginia mountains on continuous boost, we popped one of those intake manifold grommets right out of the 88 900Ts intake manifold. Here's yet another one for you, symptoms are stalling out in traffic or on deceleration, uneven idle (more uneven than usual, anyway), and a "hooting" sound from the engine bay when coming off boost. Your problem is the Turbo Bypass (a.k.a. "Hooter") valve, and yes, all the pretty girls who work behind the parts counter have heard it before if they've been there over 6 weeks. If you think you have a bad hooter valve but are not sure, put the car in 3rd gear, rev over 2500rpm, get into boost if you can, then throw it into neutral or step on the clutch. If the car dies and you're rolling, put it back into gear and let off the clutch, go home, and replace your Hooter valve.

Questions? Need a hooter valve? Just email me -

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