Bad drivability and vibration at idle

[nuclear944]

I've talked to numerous people on SC about a problem I've been having with the '89 sedan.

Nobody has been able to help me.

1.)
The symptoms are partially intermittent.
On cold starts, the car runs noticeably rich at idle. There is misfiring and vibration accompanied by an unmistakable smell of gasoline. These symptoms gradually disappear after about one-one and a half minutes of idling.
Occasionally the car starts up smoothly and doesn't run rich. This is not temperature dependent.

2.)
At any temperature, the car vibrates at idle. It vibrates more than father's SPG, so I'm assuming it's not normal. It doesn't "sound" right. The exhaust doesn't blow unevenly and the misfire isn't the kind that you would see when you pull the cord on a sparkplug. But there is a noticeable "shake" if you really look at the engine or the things attached to the engine.
This might attributed to the worn engine mounts and the noisy drive belts which contribute to the sensation of a misfire through sound.

3.)
When applying throttle at idle, the engine noticeably shakes to the side and shudders. Hesitates. This is not heavily pronounced, but it is noticeable to me.
Under low load, when starting the car from a stop, there is excessive vibration that feels like "knocking". There is no sound, but the vibration is very heavy in the pedals and steering wheel.
I swapped an air mass meter from another car (turbo), which runs the ECU richer. This eliminated the hesitation and drivability problems, but the bad idle remained.

What I've checked:
-replaced distributor cap
-checked, cleaned, tightened ALL grounds
-cleaned intake manifold and throttle body with various solvents
-cleaned AIC
-cleaned AMM
-checked for vacuum leaks THOROUGHLY
-checked for loose wiring

What I've confirmed:
-no coolant loss
-no oil loss (other than a rear main seal leak)
-I just calculated that I burn 2.8 gallons per 110 miles

I don't know what to tackle from here on. I have no funds to buy any parts.
This is not preventing the car from driving, but it is annoying the hell out of me!
I am trying so hard to prevent the car from becoming a "clunker".
I tried to replace the fuel filter. I couldn't because it's impossible.

Any help is appreciated. Winter is here and I don't want to keep driving it like this.

[sab]

Is it a normally aspirated 1989 900? If so this year and the non turbo ECUs were especially prone to having dodgy/flakey ECUs that fail... I would try putting back the original AMM but replace the ECU with a known working unit from the same year. The ECU is located on the drivers side (RHD)... so your passenger side between the firewall and door.

Try that and let us know how you go!

Vibration at idle is probably broken engine mount(s) as well as the dodgy ECU... check the mounts by popping the bonnet, hand brake on, select a gear and throttle down a bit/ clutch off but don't stall it... and see if either side of the engine rises too much. Can check visually for any cracks too.

Good luck and cheers from a sunny down under
sab

[euromobile900]

I swapped an air mass meter from another car (turbo), which runs the ECU richer. This eliminated the hesitation and drivability problems, but the bad idle remained.

The AMM doesn't run the car richer. There is no difference in AMM between Turbo an N/A. The difference is in the ECU itself. As Sab mentions, the 1989 ECU is dodgy. Since you have LH 2.4, you can get a replacement ECU from any other LH 2.4 N/A. Check out this compatibility table and then go on ebay! Shouldn't be too expensive.

Only other thing I can think of doing is checking for exhaust leaks too. And if the AMM made a difference, then one of your cars' AMMs must be bad.

[nuclear944]

Sorry, I was assuming that the turbo AMM makes it run richer. The thing is, the turbo AMM made the car virtually vibration free at low load. With the old AMM, the car vibrates a lot under load.

sab you are right; my mounts ARE gone. I resealed the front one with soft silicone as a temporary fix. But I truly need new mounts.

Damn that ECU! It's not fair- I have to spend money on something that can't be confirmed.

So I guess the verdict is that:
-it runs rich when cold
-runs lean when warm

I'll try to get my hands on an ECU.

[nuclear944]

Will this work:
87 88 Saab 900 Fuel Injection Computer Control ECU ECM - eBay (item 110565979611 end time Dec-25-10 03:24:19 PST)

[sab]

Don't think so... looks like that is for LH2.2 (87 and 88 cars) and has a 25 pin connector. You need a LH2.4 non turbo (1989) with 35 pin connector. Also the case looks a bit funny... should be an aluminium case (from what I have seen here at least... maybe they are different in the US).

Any wreckers near you where you can go to grab your own? Maybe try one of the large US wreckers like goldwing etc.?

good luck
steve

[nuclear944]

Well the rest of the ECU's on ebay are 80+ dollars. Ridiculous!!!!

I'm going to have to check the local junkyard, but the problem is everything is overpriced.....I might be in a bind here....

Thanks anyway, Steve.

[euromobile900]

Don't think so... looks like that is for LH2.2 (87 and 88 cars) and has a 25 pin connector.

Not quite--even earlier! That's a Lambda Control module for a K-jet 8v!

[nuclear944]

Never mind chaps.

Today it started horribly and spewed blue smoke. Smelled like burnt oil, coolant, and excessively rich mixture.
It smoked for most of the 10 mile drive. White smoke. It's not cold out at all. Terrible, terrible drivability, even more vibration and tendency to stall at low load. No power.
Checked dipstick and Merry Christmas- thick white substance in the oil and a lot of residue on the dipstick itself.

I will check compression if I can but with family problems I doubt that I'm going to be doing a head gasket change.

I have no facilities. There is almost a 0% chance that I'm going to be able to convince my father to do this.

Thinking about using the head gasket sealant until I can change the gasket in the spring...I know there are a lot of risks but I have no choice.

What a Christmas! Just perfect..

[sab]

Might not be a head gasket as you can get the white gunky stuff on the dipstick when the outside temp is really cold... it is a condensation effect. Drive it for a while and then check for the gunk. Also check the coolant reservoir for any bubbles coming from the feeder hose to radiator and also any floaty oil stuff on surface. I had this on my 1988 900 Aero.

You can/should also check compression to make doubly sure.

Blue smoke is an excessively rich mixture not HG failure. HG failure will show as clouds of white smoke at start up and cold driving.

Still think the issue is the ECU.

Those prices you list are pretty cheap... down here second hand ECUs start at around $250 and go up from there!

steve