I recently picked up a 95 960. For the first couple of months it was basically fine, though occasionally the engine power would drop out on hills. Now the car starts fine and runs fine for the first 5 minutes, but as the engine warms the RPMs start 'jumping' at idle, making the car move forward or backward depending on gear. Then the car will start stalling when stopped.

We pulled the codes and got 212 and 233, which I guess have to do with the O2 sensors and IAC. We swapped the IAC unit out of his 850 and switched it in, but the problem was still there. I'm not sure where to go from here and can't find any threads where there's a similar problem, so I'd appreciate any help.

 

Both of those codes are just clues but not necessarily faulty components.
Your test with the 850 part is not conclusive either, unless you know they share part numbers.

You could try cleaning out the idle valve and see if it helps, there is an ohm measurement that can help with that, don't have my volvo manual with me at the moment.

I would start by inspecting the air ducting for any leaks, the fit of the connections of the hoses for the oil recovery system. Many places where a bad hose or connection could allow unmeasured air. Another item to looking into is the MAF, especially the electrical connector, check too the vacuum hoses taking note of the rubber elbows, the will deteriorate and collapse with age.

Volvo electrical connections under the hood are not the greatest at keeping out the weather, so they will oxidize in time and allow for greater resistance which can throw off a sensor or two.

But I am betting on an air leak in the intake system, could even be a bad intake gasket, a very, very common problem with the six cylinder engines.

DanR '94 964 362,000 miles (128,000 on the new engine)

 

Try TPS (throttle position sensor) This is located on the side of the inlet manifold close to the throttle plate.

O2 sensor test would be to turn off the engine, allow to cool and retest when cold in the morning.

If the first 20 secs of operation are OK, then begins to give you a bad idle, you can confidently assume the O2 is bad. This is because the ECM manages idle speed etc until the O2 warms up and gives its readings back.

Of course nothing is as good as getting a scanner such as an Autel that can give you live O2 sensor readings.

 

Yeah, as I do more research a vacuum leak makes sense. I don't know if or when the PO replaced hoses, but he kept pretty good records and there's nothing. Would it be normal for the problem to get worse as the engine warmed? Maybe cracks expanding as the rubber heated up?

The IACs did have identical part numbers, so I guess that can be ruled out. The connector was a little oxidized so I guess that will get replaced.

I was worried about the O2 sensor as well, but the car will run normally until it warms up, usually about 5 minutes or so. Also, the engine restarts easily but the same problem starts immediately.

 

The connectors can be cleaned and tightened, so you won't have to replace any of them. The car computer does not even take measurements from the O2 sensor during warm up, so that means your problem starts when the computer makes the switch. But the other side of that is during the initial start up the fuel mixture is rich, so once it warms enough, it slowly leans out and then you have the stumbling idle. To me the richness of the cold start allow the engine to idle smoother, once it starts to warm up and lean, then any extra unmeasured air cause it to stumble. So that points to an air leak, either a hose, a crack in the air intake ducting or a leaking intake gasket.

Can you determine what cylinder is missing when it is idling badly?
Check where the flame trap fits into the air intake.

DanR

 

Ok, that makes sense. I'll check into it and post back. Thanks for the help.

 

not to hi-jack this at all.....but my new 95 960 is doing a similar thing only opposite bills....starts beautifully.....[when cold or 30-40 minutes after last run] 5-10 seconds in she starts stumbling ....now for the difference....after 5-10 minutes of warming up stumbling along she just smooths out and runs with no issues at all until its shut off and sits for 30-40 minutes or over night

note: from a "warm" start the rough idle only lasts a couple minutes as opposed to the first start of the day which can last 15 minutes - - -oh and don't even try to move it while its having its fit....almost like theres no peddle response or anything

note 2: its never died while doing it...just runs rough and then smooths out

189,000 on the clock

thank-you ill be following the thread for ideas......good luck Bill

 

I am not sure those codes relate to the IAC. Code 212 is AFR is rich / lean at Idle. 232 is O2 Sensor Signal.

You need to check for kinked O2 wires, but most likely sensor is bad.

You can check O2 sensor for voltage fluctuations from 0.1V-1.0V. It it supposed to fluctuate up and down in that range.

 

Those are different problems. When you have a poor idle like that: I would check first for fuel pressure, or leaky injectors, then for ignition (such as bad spark plugs, or wires).

One other thing -- when we ask for advice on problems like these, it would be helpful if we indicate status of Stage 0.

 

So we checked around for vacuum leaks. All the hoses were in decent condition, no visible cracks, no hissing when idling, and the idle slowed when we created an artificial leak. Replaced the plugs because we were in there, cleared and reset the codes.

I took it out for maybe 20 minutes and the problem was completely gone. No surging at idle, no CEL, better pedal response. Towards the end of the drive the CEL came back, but still no idle surge or stalling. The pedal did feel a little softer but who knows.

So to me it seems like there's no vacuum leak. Does that mean the O2 sensor is the likely problem?

 

What codes are you getting now?

 

what is "stage 0" ?

i dont want to steal bills thread ...ill start another thread this evening "the other broke 960"...lol

 

Original condition of car, reasonably-speaking. http://www.matthewsvolvosite.com/what-is-stage-0.html

 

The only code it's throwing now is 2-1-2, the O2 sensor.

I should also mention that we disconnected the battery for about 5 minutes yesterday, which I guess clears the adaptive fuel mixture?

 

You may not get the rich/lean codes until it occurs a certain number of drive-cycles. You will eventually get that code too.

It is clear that ECU reads a fault with the O2 sensor. Either there is a problem with the wiring or the sensor itself. O2 Sensors or not expensive.

The worse problem with this problem is that a faulty O2 sensor damages the catalytic converter in short order.

 

Yeah, that's what I've been reading. The OBD1 960s only have one oxygen sensor, correct?

 

I think CA cars had both -- pre- and post-Cat. Regardless, code 212 points to the front one.

 

Ok. I'm also having some trouble locating the connector-I've read it's blue and near the oil disptick, about halfway down, but all I see in that location is a grey, 2 circuit connector. Am I missing something?

 

Connector should be up on the firewall. Brickboard (here) has a nice section on 02 Sensor, but for some reason they say 3-wires. I think your sensors are 4-wires.

 

Alright, I got under there this morning. The connector was clean, but the part number I got gives me a completely different sensor, with 2 wires rather than 4. This is the one I need to order, right?

Amazon.com: Bosch 15098 Oxygen Sensor, OE Type Fitment: Automotive