Moonspin

Hi guys,
I have a S5 fc t2 for almost 2 years now and it always has this stall and over boosting issue. I am going to find a way to fix it in the spring and hope I can get some help here.

When I get the car last year, the car stalls when I come to a stop and leave the car in gear. I figured that the problem came from the leaking seal in the clutch master cylinder. After replacing with a new cylinder, the stall problem was much better but still happens frequently when the A/C is on. I did some research on the forum and found something called "clutch cut switch". If that switch is worn out, it can cause your car to stall when A/C is on. I'm wondering if anyone here has experience ordering it and replacing it? Meanwhile, even with A/C off, sometimes I still had this stall issue after driving a bit aggressive (say rev up to 6k for few seconds.....), maybe it is related to the overboosting? Anyway, the cause of this stall issuse seems to be a mix of multiple things. I've fixed the leaking master cylinder, now I hope replacing the clutch cut switch will solve it once for all.

So the other problem is the over boosting. The car is running almost on stock now with a rtek 2.1(going to replace it with PFC or adaptronic in the spring) and HKS boost control. It had a 3 inch straight pipe installed and I switched it back to stock exhaust hoping the overboosting will be gone (I thought the boost is restricted under 7 with the stock setting)....didn't work. Now I have to be really careful when putting my foot down. The boost goes up like crazy and it can get to 11 easily. If I floor it, the boost can reach 15 or higher.... With a stock exhaust and boost controller, the only thing that I can think of is the waste gate. But isn't S5 turbo's wastegate big enough for stock settings? I'm really confused now........any ideas?

Mlammert

Your stalling problem could be a number of things including the BAC.

Go check the switch to see if the clutch switch is the problem, its really simple, here's what the FSM outlines for adjusting and checking it.
clutch switch adjust/check
I know or no reason why overboosting would be related to the stalling you described and can't think of any reason why so personally I don't see it being an issue with this.

As for overboosting itself any intake/exhaust modifications can lead to it. The more free flowing you make the engine the worse the problem will get. climate (i.e cold weather) also can have effects.

You can however check a few things like making sure the wastegate actuator is operating by blowing 10ish psi into it via compressed air to see if it opens and checking the rubber line on the turbo that goes to the actuator for any cracks or leaks(I guess this would be your boost controller instead).

If your wastegate is working and you're overboosting the only fix is to port the turbo wastegate orifice itself by disassembling the turbo and using a die grinder and carbide burr to enlarge it. You can find details about how to do this along with picture here.
FC3S Pro v2.0:&nbsp How-To - 1989-1991 Kouki FC3S Turbo Wastegate Porting

These are the cheapest and most simple options I can recommend.

Molotovman

iTrader: (49)

Check the operation of your IAC valve regarding the stalling and check the rubber hoses around the turbo and wastegate actuator regarding the boost issue, it sounds like your wastegate is not opening.
If your car and engine are 100% stock consider replacing all of the rubber hoses around the engine and having your fuel injectors cleaned and reinstalled with new o-rings and grommets. Your car is 28-30 years old, things rot and require maintenance.

Moonspin

Thank you so much Malmmert. I'll check the switch this weekend. Since it's -20 here in Canada and really snowy, I cannot start the car. Will test it in the spring.
The overboosting happened in summer so I guess the wastegate or the rubbers will be the problem. Again, thanks for the kind help and detailed suggestions, appreciated.

Moonspin

Thank you Molotovman. The car idles fine, never stalled when idling, so the IAC valve should be fine? I would definitely check the rubber hoses and injectors. Do you have any idea where can I get those rubber hoses?