Bad Idle Air Control Valve? - '96 850 Topic is solved

JeffHicks · Post by **JeffHicks** » 15 Feb 2016, 10:18

Hey Gents (and hopefully some awesome gals) -

I've got a buddy's '96 850 sitting in my driveway. I've done a lot of work to it over the last couple years (mostly suspension), and it has a ton of miles on it but is a good runner.

He recently has been having all kinds of issues with it starting and running. When it's cold (15 degrees or colder), it's a bearcat to start. Then it has no power at all until it is warmed up. Take your foot of the accelerator and the engine dies.

Then, when warmed up, the engine will surge and often run up to high rpms.

I've got no codes.

Is this possibly the Idle Air Control Valve? I'm going to take it off and thoroughly clean it, but am looking for some input.

Post by **benpineapple** » 15 Feb 2016, 12:09

I was under the impression the IAC is only operating when the car is in motion. IAC might not be the only thing acting up.

Post by **theWIFES_S70** » 15 Feb 2016, 12:16

How's the Mass Airflow Sensor? I'd give that a cleaning while your at it, too.

JeffHicks · Post by **JeffHicks** » 15 Feb 2016, 13:35

I thoroughly cleaned both the IAC Valve and Throttle Body, in that order.

After cleaning the IAC Valve, the car started fine by surged. After cleaning the Throttle Body, it ran beautifully.

Upon driving, it periodically went into complete dysfunction. Would kind of idle, but could not accelerate. Then would die.

I'm hoping the IAC Valve is shot. Or is it more likely that it's the Throttle Body?

Post by **erikv11** » 15 Feb 2016, 15:03

No codes right now, even with all this engine stumbling?

Testing the MAF is free, I would do it: unplug that MAF, then start the car up and drive it around. If the problems are gone (or improved) then the MAF is bad. Of course this test will set a CEL wth a MAF code, that you will need to reset. Cleaning the MAF is mostly an exercise in contributing to the company that makes MAF cleaner; using it rarely helps unless the MAF is like visibly oily and dirty.

"Bad throttle body" is not something you hear much (at all?); how would it go bad? It seems you would be able to see any TB issues by inspection. IAC does seem possible bt a lot of things do. Hopefully it will throw some codes.

I would also check carefully for air/vacuum leaks.

JeffHicks · Post by **JeffHicks** » 15 Feb 2016, 16:59

erikv11 wrote:No codes right now, even with all this engine stumbling?

Testing the MAF is free, I would do it: unplug that MAF, then start the car up and drive it around. If the problems are gone (or improved) then the MAF is bad. Of course this test will set a CEL wth a MAF code, that you will need to reset. Cleaning the MAF is mostly an exercise in contributing to the company that makes MAF cleaner; using it rarely helps unless the MAF is like visibly oily and dirty.

"Bad throttle body" is not something you hear much (at all?); how would it go bad? It seems you would be able to see any TB issues by inspection. IAC does seem possible bt a lot of things do. Hopefully it will throw some codes.

I would also check carefully for air/vacuum leaks.

So the bizarre loping and surging is back. I unplug the MAF Sensor and it improves immediately.

No codes.

Sounds like the MAF Sensor, by why isn't it throwing any codes?

Post by **erikv11** » 15 Feb 2016, 18:00

Hmmmm well the ECU should definitely set a code when you unplug it, something is awry there. Are you sure the CEL bulb is working, does it come on when you turn the key to position II?

Regardless, it does sound like a MAF problem. Don't bother with anything other than Bosch when replacing the MAF. A used MAF will be a lot cheaper if you don't want to spring for a new one, e.g. I have a few from the junkyard waiting in the wings for if/when one of my cars has MAF trouble.

FYI I do not like to unplug the MAF when it is running, I always shut off the engine first for plugging/unplugging.

JeffHicks · Post by **JeffHicks** » 15 Feb 2016, 20:36

erikv11 wrote:Hmmmm well the ECU should definitely set a code when you unplug it, something is awry there. Are you sure the CEL bulb is working, does it come on when you turn the key to position II?

Regardless, it does sound like a MAF problem. Don't bother with anything other than Bosch when replacing the MAF. A used MAF will be a lot cheaper if you don't want to spring for a new one, e.g. I have a few from the junkyard waiting in the wings for if/when one of my cars has MAF trouble.

FYI I do not like to unplug the MAF when it is running, I always shut off the engine first for plugging/unplugging.

Thanks Erik - I'm going hunting at the local U-Pull-It salvage yards early in the morning.

If I don't find a used unit, my next question is this: Is "going Bosch" a matter of longevity, or is it more than that? I ask because I can get a lifetime warranted Dorman MAF Sensor from RockAuto for $65.

Post by **erikv11** » 15 Feb 2016, 21:57

Unfortunately, more than that. It's not longevity, the non-Bosch MAFs simply do not work in the P80 cars, they sputter and stumble to varying degrees, throw codes etc (although maybe no codes for you!). You will find reports on the forum of some people getting the Cardone or other makes to work, but those are the exceptions. It is a crap shoot and most people crap out.

If you can't find one I would send you a working one for cheap, let me know.

Edit for at the yard: the 94 and earlier MAF is different, any 95-98 will be the same as your 850. They are basically all good at the yard though I might pick up 2 if they are cheap, just to be sure. In 99 the MAF changed again. Grab a TPS while you are there, throttle position sensor on the throttle body. Those are pesky to troubleshoot, much easier to just swap one in.

JeffHicks · Post by **JeffHicks** » 15 Feb 2016, 22:20

erikv11 wrote:Unfortunately, more than that. It's not longevity, the non-Bosch MAFs simply do not work in the P80 cars, they sputter and stumble to varying degrees, throw codes etc (although maybe no codes for you!). You will find reports on the forum of some people getting the Cardone or other makes to work, but those are the exceptions. It is a crap shoot and most people crap out.

If you can't find one I would send you a working one for cheap, let me know.

Edit for at the yard: the 94 and earlier MAF is different, any 95-98 will be the same as your 850. They are basically all good at the yard though I might pick up 2 if they are cheap, just to be sure. In 99 the MAF changed again. Grab a TPS while you are there, throttle position sensor on the throttle body. Those are pesky to troubleshoot, much easier to just swap one in.

Fantastic- thanks for the information! I had a feeling longevity wasn't the issue with the off-brand MAFs.

And I do the same thing you do when I'm at a salvage yard and I see parts for one of my Volvos. That's why I have about 8 boxes of parts for cars I no longer have...

If I can't find a MAF sensor, I'll probably PM you. Thanks again!