94 850 stalls when coming to stop

volvodude850 · Post by **volvodude850** » 03 Dec 2020, 17:40

My 94 850 is stalling when coming to a stop. It starts back up fine and will idle fine as long as it's not in gear. It also will intermittently "buck" at approx. 35-40mph, and then smooths out and runs ok but will double or triple buck every few minutes.
I just replaced the MAF Sensor, the MAF housing rubber boot (hose) that comes out of the filter box and the fuel pump relay.
Any clues? Thanks, in advance, for your feedback.

93ForMe · Post by **93ForMe** » 03 Dec 2020, 18:37

Perhaps your idle air control valve is gunked up? It controls the air going into your intake when your foot is off of the accelerator and the throttle is closed. It is pretty easy to get to and remove to check . It sits in front of your vacuum tree and it has a hose going into it from the tube that goes from your filter box to your throttle body and a hose that then goes into your throttle body. You also need to remove its sensor cable by pushing down on the wire locking piece on the cable side and pull it out. If you remove it and shake it ( gently ) by twisting it side to side is should clunk back and forth. Look in the holes where the hose goes in and see if the float is moving freely, or if it catching on gunk. It should be very springy and should move all around very freely if it is in good condition.

I cleaned mine out by soaking it in carb cleaner with the IACV standing up so that the carb cleaner only goes inide the holes at the bottom, but does not travel up to where the sensor connector goes. Use cotton swabs to clean out any gunk with car cleaner until the float moves freely. They can get very dirty!

volvodude850 · Post by **volvodude850** » 03 Dec 2020, 18:58

cant thank you enough for your suggestion 93ForMe. Not really knowing what Im doing, but not afraid to try, it's always awesome to get solid advice. I will post the result in spirit of sharing. thanks again!

93ForMe · Post by **93ForMe** » 03 Dec 2020, 20:10

Hey no problem. I was having one second thought, you should probably use throttle body cleaner for it instead of Carb cleaner just to be safe. I don't know if the IACV has a coating like throttle bodies do, but throttle body cleaner will work just as well, and won't remove any protective coatings if they are present.

Also, if the hoses have not been removed before, the hose clamps will have been crimped on at the factory. They will have to be snipped off where they are joined, so you will want a couple of adjustable hose clamps to put back on.

Good luck! I hope this is your problem, because if it is, it will be an inexpensive and easy fix.

volvodude850 · Post by **volvodude850** » 03 Dec 2020, 23:27

Thanks for the heads up on the throttle body cleaner. I do have a can of maf sensor cleaner. Do you think that would be safe to use? I also hope your suggestions lead to a resolution here...inexpensive is always a good thing! If cleaning everything out still doesn't resolve the issue I may attempt to access the ECT valve as suggested by JIm Peisker in his blog that Matthew published on this website. It refers to a 97 850 wagon that suffered from the same stalling issues as my 94 850. I am assuming there wouldn't be much difference in the engine specs thereby allowing me to safely suspect that ECT to possibly be the culprit; in your opinion is that a safe assumption? ...thanks again for attempting to help!

93ForMe · Post by **93ForMe** » 04 Dec 2020, 08:28

MAF cleaner should work fine for cleaning your IACV.

As for the Engine Coolant temperature sensor. Those can cause a lot of problems as well. When they start to go you may notice things like the fan going non-stop and hard starts. They are easier to diagnose because they should throw a code on your OBD1 computer. Port A7 should flash a 122 code ( I believe ) if it is going bad. Also you can check the Ohm reading by unplugging the connector and inserting the leads of a Volt/Ohm meter. Below is the expected ranges for a good sensor:

COOLANT TEMPERATURE SENSOR RESISTANCE TABLE
Temperature – F ( C) Ohms
32 (0) ………………………………………. 7300
68 (20) ……………………………………… 2800
176 (80) ……………………………………… 300
212 (100) …………………………………….. 150

The connectors can get pretty corroded as well, so those are good to clean as well if they are turning green.

volvodude850 · Post by **volvodude850** » 04 Dec 2020, 10:08

Ok, understood. Now it's time to pop the hood and get to work. Thanks again 93ForMe for all the great insight and data. I will let you know what I find.

volvodude850 · Post by **volvodude850** » 27 Dec 2020, 12:09

Sorry for the delay in the response...a trip to Mexico and holidays have kept me from my 850. After putting in new MAF, boot and fuel pump relay, I pulled the IACV and inspected it and just as you suspected the mechanism inside was frozen. The cleaner freed it up and restored it to the springy state where by it rotated and moved freely. I cleaned the pins and the lead as well, reinstalled and fired up the volvo. Wow, it idles great at start up and maintains at approx. 900 rpms. with a minor amount of rough idling that seems to get better as it warms up to norm op temp. . . however it will eventually and slowly decrease in rpm and die. If I drive it it will run fine but dies when coming to a stop. I can keep it running if I keep the accelerator involved with shifter in neutral and then back into gear to get going again. I tested the pins with voltmeter and it's in range 10-14 ohms, tested the leads and out of each lead (1,2,3) I get battery voltage. Should I suspect the ECT? Cam sensor?

93ForMe · Post by **93ForMe** » 29 Dec 2020, 15:23

Just for kicks, before you start in on more part swapping, pull the IACV again and see if it has refrozen. I just remembered that when I cleaned mine, the first time I sprayed it out it seemed to move freely at first, but all I really did was loosen the gunk up and it re-hardened when it dried. To really get it cleaned out, I stood it up in an plastic container and soaked the mechanism part overnight in mineral spirits.

If that doesn't work, I'm really not sure what else would be affecting the idle. The ETC does cause a number of issues when going bad, but I can't say that I have heard of it causing your specific problem. I am, however, not an expert!

Cookeh · Post by **Cookeh** » 30 Dec 2020, 04:03

Both cam and crankshaft sensors can cause idling issues leading to stalling. To my knowledge, ECT faults typically cause rich running and hot start issues more so than stalling problems.

Both can be tested in the car with a voltmeter. Crankshaft you simply unplug and test for resistance, the camshaft however requires backprobing with the ignition in PosII. Can't recall the resistance and voltage values you're looking for off the top of my head, though a quick Google should reveal all. When I have a spare minute later I'll update this, if you haven't already found it!