Saab 9-5: engine runs rough and wants to die. Engine light is on.

[DarthBoots]

Did you check for Limp Home mode? I had a broken brake booster vacuum hose-fixed it and I had the same symptoms. A couple mechanics said it was a crimped vac hose-but that didn't sit well- so I checked and sure enough, it knocked itself into limp home mode. I reset it, and so far so smooth

[borderwave2]

I've had a similar intermittent problem lately and I was just about to post a thread when I found this, so I'll ask here instead.

2006 9-5 "Aero"

Symptoms seem to be the same. I'll be driving along, and when I close the throttle, or have it just a bit open, the car struggles to find the idle speed. It'll drop to 500-750 RPM (or even 250 on occasion, causing it to almost stall). Once it did stall just as I parked, and that was the only time that a code was thrown (P0300 Random Misfire). I've read a number of posts on various forums about this and the following were done, either by me or a mechanic:

Cleaned throttle body - wasn't overly dirty
Cleaned MAF
Checked for vacuum leak - none found
Checked spark plugs - a little black, but nothing that should cause concern (NGK PFR6H-10, installed about 9 months ago, used for about 40,000 km so far)
DIC appears fine, no code, brand new OEM unit installed same time as spark plugs

This issue has happened 4 times so far. The last three times it's happened, it occurred right after filling up at the same gas station. I think the 1st time was there too, but I can't be sure. I always fill up with their premium (91 octane), which is advertised as containing no ethanol. Could this be due to bad gasoline? It happens right after I fill to max, after I drive for ~10km and let it sit for a bit, the problem doesn't return.

Any advice would be greatly appreciated as this is driving me nuts.

The 9-5 aero calls for 93 octane IIRC right?

[ile2010]

Did you check for Limp Home mode? I had a broken brake booster vacuum hose-fixed it and I had the same symptoms. A couple mechanics said it was a crimped vac hose-but that didn't sit well- so I checked and sure enough, it knocked itself into limp home mode. I reset it, and so far so smooth

Not in limp home mode.

[ile2010]

The 9-5 aero calls for 93 octane IIRC right?

The 91 is the best available at most pumps around here.

In any case, I've eliminated the bad gas possibility. It's probably my filler neck or purge valve. If I keep filling until the pump shuts off, it's already overfilled (I know because attempting to top off will result in spillage immediately). Since I started filling to 90%, the problem disappeared.

[Ohioan]

A few ideas, ile2010:

1. Is the throttle body in "limp home" mode, perchance? Have you checked it lately?

2. Even though it's "clean," the throttle body could still be bad. (Mine looked clean, too.) I read elsewhere on here that a common failure mode for the throttle body is degradation of the wires/electronics inside it. I'm thinking this was the failure mode of my throttle body, though I've never taken it apart to look at it.

3. It's doubtful this is the culprit, but I am wondering if poor idle could be caused by low fuel pressure due to a clogged fuel filter or faulty fuel pump. Has the fuel filter ever been replaced?

Edit: Oops, I see that some of my questions have already been answered. Sorry about that...

[Ohioan]

Oh, and just a follow-up:

I replaced the throttle body two and a half weeks ago, and the engine runs perfectly. So I'm guessing that was the culprit.

I still have the old throttle body. Not sure what to do with it. I'm thinking about taking it apart to look at the electronics/wiring to see if I can identify the root cause of failure.

[DanielZ]

I had a "rough running" engine for a while but it was so intermittent I didn't want to start switching parts.
Is it uncommon for water to get into the fuel lines? The wife drives this car and usually won't get a full tank and instead just gets a smaller amount of fuel. this can cause water to gather in any tank and the way the weather has been these last months here ... cold and damp is only the start of it.

So I forced her to get full tanks and tipped some Kemetyl (ethanol, 1- propanol, 2 propanol mixture) to bind any water.
And it's been fine since...

Anyone else who's had issues with water buildup in the fuel? Didn't want o start a new thread on this.

[nordwulf]

So I forced her to get full tanks and tipped some Kemetyl (ethanol, 1- propanol, 2 propanol mixture) to bind any water.
And it's been fine since...

Anyone else who's had issues with water buildup in the fuel? Didn't want o start a new thread on this.

I had a hard starting engine once and used a container of Isopropyl alcohol (Heet). This seemed to have fixed the problem because it was fine after that. I assume Kemetyl and Heet are the same thing.

[DanielZ]

I had a hard starting engine once and used a container of Isopropyl alcohol (Heet). This seemed to have fixed the problem because it was fine after that. I assume Kemetyl and Heet are the same thing.

Probably is.
Anyway, my problem was also a worn battery. Replaced with a new one a few days ago and now it all works fine. Winter has come...