1995 850 rough idling continues, att J Blackburn

Buffalo Surfer · Post by **Buffalo Surfer** » 13 Sep 2011, 13:06

I tried your advise JBLACKBURN to disconnect the neg batt connector, pressed the break pedal , reconnected terminal, and the car still idles ruff at times after sefveral trips. Notice sometimes not always. So it has not changed (Remember MAF Trouble and open air flow?). It coughs at times when idling and sometimes purrs like a kitty. Very unpredictable, but when it coughs it such I have to put in neutral to alleviate the knocking, seems like it stops considerably when i do that. Actually its like if it was the transmition messing up ( I flushed the trans a year ago). Could it be the distributor cap and rotor? never chanhed those since I have had the car (3 Years).

Post by **vjaneczko** » 13 Sep 2011, 13:46

Checking your previous post; do you still have the cat error? It sounds like you may have a plugged cat, which means the materials inside are falling apart. Give it a few 'love taps' with a rubber mallet or your show and listen for anything rattling around inside.

Other things to check would be the spark plug gap: .028 on plain ol' copper plugs is best.

May want to make sure that your airflow is clean; idle control valve, throttle body, etc. Carb cleaner should do it. I just used 1/2 a can on my ICV alone, so be prepared to use a lot of it!

The MAF: you mentioned 'rebuilt' in your last thread. Volvo's have problems with anything other than Bosch. You can try cleaning it but make sure you use MAF cleaner for it - anything else will destroy it.

Any work done on the fuel system lately? May be the fuel filter or the pump (check the pressure at the fuel rail).

I'd think if the car idled poorly all the time, it might be the distributor but I don't think that's your problem.

Could be some vacuum hoses are shot, which are always fun (not!) to check/replace. Check out Stage 0 steps and use it as a checklist:
https://www.matthewsvolvosite.com/2009/0 ... s-stage-0/

Post by **jblackburn** » 13 Sep 2011, 21:24

Vjanesko's got a good list for you above. I'd start by double-checking there are no vacuum leaks (a can of carburetor cleaner sprayed around vacuum lines will help you find small cracks).

Other question: does the erratic idle happen only once the engine is warmed up, or on a cold engine as well?

Buffalo Surfer · Post by **Buffalo Surfer** » 15 Sep 2011, 11:44

once its warmed up it starts

Post by **jblackburn** » 15 Sep 2011, 12:40

OK, good...you can probably cross some things off of your list now. That means it's happening when the car goes into closed loop mode once the engine and O2 sensors warm up.

Vacuum leaks are even more of a suspect now. They can fool the O2 sensors into giving bad readings.

Fuel/ignition problems are probably not your issue. Something is off with a sensor - if you cannot find any vacuum or exhaust leaks, this may well be a bad O2 sensor.

Buffalo Surfer · Post by **Buffalo Surfer** » 16 Sep 2011, 11:42

is the O2 sensor the MAF? or the CAT( Both of them?)

Post by **jblackburn** » 16 Sep 2011, 12:55

Nope; the O2 sensors are affixed on top of the catalytic converter under the car. You would only be concerned with the front one, just after the exhaust pipe swoops under the car.

Your car doesn't sound obnoxiously loud, does it? An exhaust leak can cause all of this same stuff to happen by tricking the sensor.