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Replaced Dash Cluster - Now Car Won't Idle ('89 SAAB 900)

Since the odometer had long since stopped on my 900, I figured I’d replace it since I was already under the dash to replace the heater control valve. Long story short: I got the heater control valve installed fine, pulled the instrument panel and replaced the dash cluster. Everything lights up, the gauges work, it’s all fine.

Except one thing. Now the car won’t maintain an idle.

Things I’ve tried/checked to diagnose or fix it:

- Ensured all electrical connections on the cluster are fine (particularly speedo and speed sensor)

- Checked to ensure all connections to dash instruments are good

- Recharged the battery - just in case

- ?

Possibly related, but not likely, is a recent change of the fuel filter. I verified that it was connected correctly, plus it ran fine when I tested it, which was before the cluster/heater control valve installation.

None of these things have yielded in a running car. It still cuts out after a few seconds of idling and responds poorly to the gas pedal - indicative of a vacuum leak? My concern is that somehow the AMM or TPS got fried. I have tried a replacement AMM and no change, though I haven’t re-calibrated or changed the TPS yet. My hope is that somehow I bumped a hose while I was under the dash and it’s causing some mysterious vacuum leak. Can anyone confirm this as a valid hypothesis? If I’m overlooking something glaringly obvious, please let me know!

Well, they do have a maze of hoses in there and I would advise connecting a vacuum gauge to an intake port to verify if there is a vacuum leak or not.

Some of the most likely trouble spots for vacuum leaks could be the mode control switch. (the one with the multiple vacuum line connector that attaches with the 2 locking ears. Fully seated with ears locked?)

Cruise control disengagement hoses near the pedal assembly.

Turbocharged car? If so, is the boost gauge hose connected to the cluster?

Likewise, if the car is turbocharged there is an overboost switch near the clutch pedal that has a number of vacuum hoses. It’s easy for these hoses to get knocked loose or crack due to age and dry rot.

Those are about the most common sources of air leaks and hope some of that helps.

Whoops, I should’ve mentioned that it’s a non-turbo without cruise.

The mode control was previously disconnected, but I did get it fully seated with the metal locking collar. Unfortunately, that didn’t make a difference yet. Tomorrow, I’ll delve a little deeper and see if something is off, without making it worse, hopefully. Is it possible that any HVAC leaks or disconnections could be causing this? It doesn’t seem likely to me, but my understanding is these cars have a very delicate balance and won’t run if it’s upset.

SAABs are pretty cantankerous when it comes to air leaks so it’s entirely possible a vacuum leak could be behind this. Lacking a vacuum gauge, you could try pinching off the vacuum source between the engine and the vacuum resevoir to see if the problem goes away.

I went through something like this a year or so ago with my Turbo when it developed an air leak. Wouldn’t idle well, stumbled badly, etc. and as luck would have it the leaks were due to cracked hoses at the overboost switch.
As you no doubt know, access underneath a SAAB dash is pretty much for munchkins.
It only involved about 3 pieces of hose totalling about 5" altogether but it was a minor nightmare to get in there to change them.