1998 S70 T5 Sputters at Idle. on braking, poor acceleration

tatsnturbos · Post by **tatsnturbos** » 22 Jul 2013, 10:00

My 98 S70 T5 sputters at idle, whenever I brake and is throwing misfire codes on cylinder three and five. When I accelerate, it takes forever to get going. I sent it into a shop and they checked my whole ignition system, everything looks fine. No vacuum leaks either. My friend suggested it is the BCS but I am confused, as I was looking online on how to replace the BCS and am seeing that people are saying that 98's dont have a BCS, but a TCV instead.

Would a broken BCS/TCV cause my car to act like this? Does my car have a BCS or TCV? And does anyone have an installation guide for this? I am a beginner at doing repairs on my own, so please bare with me if the answers are obvious to my question.

Thanks!

Post by **mercuric** » 22 Jul 2013, 11:51

tatsnturbos wrote: Would a broken BCS/TCV cause my car to act like this?

Very doubtful. This valve controls pressure to the wastegate. If it's defective, your boost will either be above or below expected levels, depending on the failure mode. It does nothing at idle or during deceleration/braking.

Does my car have a BCS or TCV?

Yes. BCS refers to "boost control solenoid" and refers to the older-style boost pressure control devices found on 850s. TCV refers to "turbo control valve" and references the newer-style boost pressure control device found in the S/V/C70 cars. "Officially", in the parts guide both are simply called a "solenoid", but folks tend to refer to them as BCS/TCV. The operational concept is similar, just an updated design.

And does anyone have an installation guide for this? I am a beginner at doing repairs on my own, so please bare with me if the answers are obvious to my question.

The valve is extremely simple, it is a small device near the passenger's side of the airbox with three air hoses connected to it. Attached is the turbocharger parts pictorial which depicts the valve as item #16. The only consideration for replacing it is to connect the hoses to the same ports as they were disconnected from. Mark the hoses and/or take a picture before removal.

Regardless, your problem is likely elsewhere. Given it is throwing cylinders 3 and 5 only, and not the random code, I'd start by checking the condition of the plugs, and comparing plugs from 3 and 5 to the others, noting if they look different.

As far as the shop, looking fine and actually being fine is a different matter. When was the last time the plugs, wires, cap and rotor were replaced? What sort of plugs are in the car now?

Post by **rspi** » 22 Jul 2013, 11:52

To start, if the car is misfiring you need to figure that out. What is the fuel pressure at idle and while driving? When was the car last tuned? How old are the wires? Do you have a turbo boost gauge?

Not sure what your friend calls the BCS but I don't think the TCV would cause misfires.

tatsnturbos · Post by **tatsnturbos** » 22 Jul 2013, 12:45

Plugs were done about 2 months ago as well as the wires. I have NGK plugs in right now. The shop regapped them last week when I took it in. They also replaced the cap and rotor at this time. I do not have a turbo boost gauge.

He said he thinks its the BCS because it still spools up fine after accelerating for a while, theres so much more lag now. He checked for vacuum leaks and nothing. I'm thinking I should replace the fuel filter. Should I even attempt the BCS?

Post by **matthew1** » 22 Jul 2013, 12:51

Did this behavior appear after you had the shop work on it?

tatsnturbos · Post by **tatsnturbos** » 22 Jul 2013, 12:59

What happened was my boyfriend installed my suspension for me and he was driving it around trying to break in my suspension. He said it started misfiring and hiccuping hard.

I got it towed to the shop and they checked over my ignition system. They said it was working fine. It was showing random misfire, misfire on cylinder three and five. He cleared the codes and scanned it again after cleaning my MAF and the random misfire code was gone, as well as misfire on cylinder 5. I went to the shop to pick it up, as it is my only means of transportation and he scanned it again before I took it, the misfire on cylinder five code came back. He unplugged my MAF and said to drive around with it unplugged till I can get it back in the shop.

I didnt have enough money to bring it to the shop again, so my mechanic friend offered to look at it. He checked my vacuum lines and found no leaks. This is when he suggested I replace the BCS.

And now here I am... completely confused.

Post by **matthew1** » 22 Jul 2013, 13:15

The problems started before the shop. This is important because we're tying to eliminate variables to narrow down the source of the misfires.

If it happened after the shop, I would have said take it back, it's their problem.

Let's eliminate plugs, wires, distributor, and ignore TCV for now. Look at fuel, like RSPI suggested.

tatsnturbos · Post by **tatsnturbos** » 22 Jul 2013, 13:24

How do I check the fuel? What am I looking for? Sorry, like I said I am REALLY new to this.

Post by **matthew1** » 22 Jul 2013, 13:35

Buy a fuel pressure gauge at an auto parts store or online.

tatsnturbos · Post by **tatsnturbos** » 22 Jul 2013, 13:49

Ill try that, thanks Matthew!