Intermittent rough idle or no-start; no codes (96 850)

mc510 · Post by **mc510** » 05 Jun 2011, 14:14

I have a base model 1996 850 wagon with about 180k miles. Maybe 1 time out of 100 when I start it up, the idle is crazy rough; it can barely keep running. Usually if I shut it off and start up again it will be fine, though sometimes I have to do this maybe 2 or 3 times. On a few occasions, it has refused to start at all; it kind of seems like this is the same thing as the rough idle, except to such a bad degree that it can't even start up (though this is totally a guess). Yesterday I had to crank maybe 25 times before it started, and then it seemed to run normally. But I'm now a little wary of driving it anywhere I can't walk home from.

Check engine light is not on; my el-cheepo OBDII readers shows no codes; VOL-FCR shows no codes.

I've had the car since 140,000 miles, and I've not replaced any of the sensors. I suspect that the previous owner was not very diligent either. I've been assuming that when a sensor goes bad that I'll either get an error code or fail California smog check, neither of which has happened. So maybe a sensor is shot but somehow isn't giving a code? Or???

mc510 · Post by **mc510** » 06 Jun 2011, 14:00

After reading a lot of threads about rough idle, it sounds like I should try cleaning the MAF (cheap, easy, and can't hurt). It also sounds like maybe low fuel pressure, a vacuum leak, or a faulty ECU might be at play ... at least, these solutions came up for other people with rough idle. Do any of these sound like likely culprits for my intermittent rough idle with no error codes? Thanks

mc510 · Post by **mc510** » 11 Jun 2011, 12:07

Okay, I just cleaned the MAF. It didn't look dirty, but who know, maybe it will make a difference. I guess I'll just keep driving and see what happens. I'd be most appreciative, though, if anyone has any other theories ... or, especially, any tests that I should apply the next time it turns all stumbly on me or refuses to start. Thanks

Post by **pkc303** » 11 Jun 2011, 14:05

It sounds like a vacuum hose leak. They are hard to see, especially the elbows. I'll feel all the vacuum hoses, and if one crumbles or gets your fingers black with rubber, then replace it. Your problem sounds exactly like a vacuum hose going bad.

mc510 · Post by **mc510** » 11 Jun 2011, 19:18

Thanks pkc303; I'll check that out. I guess I need to find a vacuum hose diagram, then inspect all of them ... should I do it with the engine running to see if fiddling with the hoses triggers the stumbly idle?

[edit] Aha; MadeInJapan posted a vacuum hose diagram already (thank you!!) and Bay 13 has a nice writeup. Only three hoses; should be less of a headache than I had feared.

mc510 · Post by **mc510** » 19 Aug 2011, 15:41

Well, it's becoming much more frequent now that the car won't start. It cranks fine for maybe 3 seconds, then stops cranking, as if the battery is dead ... but it isn't; I can try over and over again to crank it, though each time it stops by itself after a few seconds. Eventually it will catch and start, run rough for a few seconds, then settle down.

Still no codes. I've cleaned the MAF; checked the vacuum hoses; checked for fuel pressure (at the schraeder valve in the engine compartment). Any other suggestions before I throw in the towel and start throwing money at the local mechanic?

Greybeard · Post by **Greybeard** » 19 Aug 2011, 20:08

I cleaned my MAF sensor yesterday afternoon. It still ran terribly. Surging and dying. There is a test for MAF when this is happening that I read somewhere else on this site. Unplug the lead to the MAF. Start engine. If it runs smooth, it's probably the MAF. So I did the test and it ran smooth. I quit working on it for the day and then came home tonight and tried starting the car again. It ran smooth all hooked up. I read somewhere else on this site that a guy had his car running rough after cleaning the MAF and he attributed it to the cleaning fluid not being totally dry. I think that was what might have been wrong with my MAF too, because after 24 hours of sitting in the drive in the sun, it is running smooth. The fluid must have totally dried. Who knows? I also closed one eye, stuck my tongue out and crossed my fingers when I started the engine. Maybe that did it!

Post by **Ozark Lee** » 20 Aug 2011, 05:14

They will always run very rough right after the MAF gets cleaned. The ECU may also need to re-learn if the MAF was on the edge of its limits. You will need your radio code of course but you can disconnect a battery cable for a few minutes and force the ECU back to its factory presets. For the first tank of gas after that your mileage will suck as the ECU re-calibrates.

...Lee

alexk243 · Post by **alexk243** » 18 Feb 2013, 20:20

Quick question. How do you clean your MAF? Just spray carb and choke on it?

Post by **erikv11** » 18 Feb 2013, 22:54

Not carb cleaner, that is way too harsh. Buy "electronic parts cleaner" that will leave zero residue or CRC even sells it in a can labeled "Mass Air Sensor Cleaner"

Here ya go https://www.amazon.com/CRC-05110-Mass-Se ... B000J19XSA