94 850 stalls when coming to stop

[abscate]

Remember that resistance testing on Hall effect type sensors give you confirmed failures if open or shorted , but don’t give you good indicators of a proper functional switch.

Resistance on coolant sensors is definitive, though

Condition of the electrical connectors and wiring is just as important as sensor parameters

[Cookeh]

Very good points, thankfully Volvo also provides details on how to test the wiring in the troubleshooting of these items. This link contains crankshaft testing, and the attached link covers camshaft.

[volvodude850]

Well, you may not be an expert 93ForMe but your intuition was right on the $$. I removed the IACV and soaked it overnight in mineral spirts, gave it another good clean mineral spirt rinse, dried it out with a blow dryer and reinstalled it. It fired up and idled much better with little to no tach wobble. I had to let it warm up to norm op temp before I could put it in gear without stalling however. Once it allowed me to put it in gear without stalling I test drove it at various speeds conducting abrupt stops. The first couple of x's it did stall but then after about 5 miles it remained at idle with every stop, with just a couple of exceptions. A couple of x's when coming to a stop the tach dropped down to zero as if a stall was about to occur when suddenly the engine surged back up to 1000 rpm's and maintained idle. The other symptom is a bucking that occurs when accelerating, after a complete stop, to approx. 35-40 mph and approx. 2500 rpm's. The engine will sputter buck as if either it was deprived of fuel or a spark misfire. This symptom is intermittent and doesn't seem to be consistent in the pattern. Any ideas about that one? Thanks again for helping solve the IACV problem and thanks also to Cookeh for the input regarding the crankshaft sensors. I will test those to get the readings on both the cam and the crank as directed. I will need to lookup (Google) the method of "backprobing" as I'm not familiar with that move... lol, I'm learning new things every time I attempt a DIY repair on this Volvo. I'm thankful to Matthew for establishing this site, as it's been invaluable to me in my effort to keep my 850 out of "the shop".

[93ForMe]

I am glad that things are getting better for you! I was thinking about your problem the past couple of days and I was wondering about your throttle position sensor. This is another idle thought ( pun intended ( sorry )). If your throttle position sensor is getting dirty it could be giving bad readings causing the bucking issues and possible loss of power at times. It may also not properly sense when the throttle is full closed, leading to stalling issues. My 93 850 was having bucking issues at around 2100 rpms until I removed the throttle position sensor from the throttle body and gave it a good cleaning with electronics cleaner ( your MAF cleaner should also work just fine ). It was really oily and dirty. After I cleaned it, the bucking problem did go away. It is a very easy part to remove and clean, although I do forget the size of allen wrench that I used to remove it, unfortunately.