1996 850R Occasional Hesitation at Idle

wackenhut · Post by **wackenhut** » 08 May 2018, 22:10

Hi,

I am not sure what could be causing this. The best way to describe what is happening is when the car is running and shifting through gears everything runs smoothly. I notice that occasionally when I am stopped at a light or when in traffic and idling, I feel what is a slight hesitation from the engine (similar to the feeling when you shift from Park to drive or to reverse). Because it occurs when idling, I do not think it could be related to the transmission. Could this be a spark plug issue? If the intervals are 30K for spark plugs, then I am due for them to be changed. Any help is appreciated.

Thank you

Post by **erikv11** » 09 May 2018, 08:30

It's not the radiator fan turning on, is it?

I would check the MAF. Drive around for a couple days/hours without the MAF plugged in.

Plugs problem seems unlikely.

Post by **rspi** » 09 May 2018, 09:28

I'm having the same issue. My guess would be the MAF. Every once in a while my idle drops for a second and goes back to normal.

wackenhut · Post by **wackenhut** » 09 May 2018, 21:02

It is strange cause the MAF sensor is brand new.

Post by **erikv11** » 09 May 2018, 21:23

Is it Bosch? If it's brand new and not Bosch, that points squarely at the MAF. There is a long, long history of aftermarket MAFs not working on P80 cars.

wackenhut · Post by **wackenhut** » 11 May 2018, 23:02

It is a Bosch. If I unplug the MAF, won't the car shut down? Also, is there a way to know if it is the radiator fan? I do not think it is though.

Post by **erikv11** » 12 May 2018, 00:22

Unplug the MAF before you start the car. Then start it up with the MAF unplugged. This will set a MAF code but the car should run fine. It is just running a little rich. Drive it around for a few hours or a few days, see if the problem persists. Turn the car off before you plug the MAF back in.

If it is a new Bosch MAF (not a remanufactured one?) then I would expect it to be OK, is it is the right part number. Also the MAF connectors can be an issue on these cars, see http://volvospeed.com/volvo_repairs_how ... ensor.html.

Another thing that can cause this kind of behavior is a small vacuum leak, could be hard to track down if it is intermittent. Is the elbow intact on the passenger side end of the intake manifold?

Post by **abscate** » 12 May 2018, 05:06

Pull out those plugs and have a good look at them

You don’t need fancy ones on these cars, Bosch copper are fine, single electrode.

While doing this job, look hard at the wires, cap and rotor condition too.

Post by **jreed** » 12 May 2018, 06:06

It might also be worth removing the automatic idle control valve and inspecting it for excess residue build up near the rotating plate that controls the air flow. When the plate sticks, the car can't keep the idle steady. On my car ('97 855 205k miles) it has happened at idle during hot weather--cleaning it out fixes the problem. It's pretty easy to access and clean.