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Edward
Edward, ASE Certified Technician
Category: Volvo
Satisfied Customers: 3136
Experience:  I've had 10 years of experience on the car line at 2 Volvo dealerships, Quality level Volvo tech.
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volvo stalls infrequently

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My '97 volvo stalls when I come to a stop or slow down in traffic. The car will start back up shortly after, but then stall again if I slow down. This only happens for a couple days, and then it will be fine for a month. I have taken it to 4 mechanics including the dealership, and no one knows what the problem is! The dealership said the thermostat needs repairs, but that it would only improve my fuel efficiency, not fix the problem. Any thoughts?


Edward :

Hello and thanks for your question. My name is XXXXX XXXXX I will do all I can to help.

Edward :

Let me first ask, did you have the throttle body cleaned by chance?

Customer:

I did a full tune up, and not sure if that was included. The report says they did an inspection for the carb throat and choke for cleanliness..?

Customer:

It also says inspected fuel injector throttle, and I did the carbon clean system flush..

Edward :

Alright, It's possible they cleaned it, but, I can't 100% sure. They process isn't that difficult. You basically remove the fresh air hose from the throttle body, and spray some carb cleaner into the throttle body where the throttle plate is, take an old tooth brush, and scrub the body until all the carbon and deposits are clean from the aluminum housing.

Edward :

What happens is, there is a set amount of metered air that is suppose to bypass the throttle plate, but, overtime it gets dirty, and not as much air can bypass the plate.

Edward :

Is this turbo or non turbo?

Customer:

It is an 850 stationwagon

Edward :

Alright, station wagons can be turbo's as well, but it would have a turbo boost gauge in the center of the instrument cluster.

Edward :

If it's not turbo, then there will be a corrugated plastic pipe coming from the air filter box to the engine,

Edward :

I have seen that plastic pipe get holes in it, and deteriorate over time. Down in the plastic pipe in the corrugations it will crack and break and you spread that pipe apart and you can see cracks in it. That can cause your problem.

Customer:

I don't think it is turbo. Do you think a dirty throttle body would cause the car to stall intermittently and then be okay for week?

Customer:

One mechanic did check "the vacuum seal?" but found no problem except for my gas gap which he replaced.

Edward :

It's possible. but, it may be only part of the problem. The idle valve is what controls the bulk of the idle speed when you let off the throttle.

Edward :

Is the check engine light on now when driving?

Customer:

no

Edward :

Alright, if the light isn't on, then most likely there are no trouble codes stored.

Edward :

Which is good.

Edward :

What I would do first, is, inspect the fresh air pipe, from the air filter box, to the engine, and make sure it has no holes in it, If there are any holes in it, the mass air flow sensor gets bypassed and then the computer can't monitor how much air is coming into the engine.

Customer:

It also will skip and lurch sometimes when driving, which usually indicates that the car is going to stall when I come to a stop or slow down.

Edward :

If that hose has holes, then replace it, If that hose doesn't have any holes, then remove the fresh air hose from the throttle body at the engine, and spray it with carb cleaner and wipe it clean with a rag. Make sure where the throttle plate returns is clean.

Edward :

That lurching is the idle valve supplying full bypass air to the engine trying to make it keep running..

Edward :

It's possible the idle valve itself could be defective, but, I would check the fresh air hose for holes, and clean the throttle body first.

Edward :

That usually fixes 850's. but I have had to replace idle valves for being stuck as well.

Customer:

okay, so I should check the fresh air pipes for holes, the throttle body for cleanliness, and check the idle control valve.

Edward :

That is correct.

Edward :

and in that order.

Customer:

Okay, I might be back tomorrow.

Customer:

Thanks

Edward :

I have also seen the mass air flow sensor cause a stumble at idle, however, that usually sets off a check engine light, and if yours is off, then I doubt that is the problem.

Edward :

Alright, Thank you. Let me know if you have any further questions.

Customer:

Do you think a broken thermostat could contribute to the problem?

Edward :

Does the temperature gauge run about 1/2 way up when the engine is warmed up? or does it only run about 1/4 of the way?

Edward :

When they break, the gauge will run about 1/4 of the way up, it should ride in the middle usually.

Customer:

The dealer said that the thermostat needs to be replaced, but that it would not fix the stalling problem, only help with fuel economy. I was just wondering if it is possible that it might actually fix the problem.

Edward :

No, it won't fix the shutting off problem. But, it may set a check engine light if the engine doesn't get up to operating temperature. If the gauge doesn't run in the middle, then I suspect it's broken, however, if the gauge does get up to the middle, then I would say the thermostat is alright. If you follow the upper radiator hose to the engine, Those 2 bolts that hold the thermostat housing to the engine need to be taken off, then the thermostat is right there, It only takes me about 15 minutes to put a new thermostat in an 850.

Edward :

and the factory Volvo thermostat is a Wahler 195 degree thermostat.

Customer:

Thank you so much! one last question. They mentioned the mode selector switch and the aux drive belt. Do you think these could be related?

Edward :

the mode switch is for transmission Sport or Economy, it would not contribute to the shutting off problem.

Edward :

The drive belt, (if cracked) should be replaced, you can look at the ribs in the drive belt and tell if it is cracking or not. If it's not cracking, then I wouldn't replace it, but if it is I would, however again, the drive belt whether cracked or not, would not cause the vehicle to stall.

Customer:

Thank You!

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