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Fast idle

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Old 05-19-17, 08:37 AM
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Fast idle

Hello everyone,
I own a first gen gsl-se, but am posting here because I have an S5 intake. The problem is that the adjustment screw for the fast idle hat rests on the thermo wax never seem to separate even after the car is fully warm. If I push down with a screwdriver on the fast idle cam the car will want to stall. M thinking is that somehow by the thermowax plunger not opening all the way and not having separation it's allowing air into the intake. This may be the reason why I cannot get a perfect idle. The FS2 says that after the car is fully warmed the screw should not be resting on the thermowax plunger thingy. Can anyone confirm?
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Old 05-19-17, 12:05 PM
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The screw always rests on the plunger, as it heats up, the plunger moves up and pushes the screw, which moves the cam, which separates from the peg on the throttle body shaft. If the engine is hot and this cam is all the way rotated out, which with a working setup should, the screw isn't your problem

Source
Page F1-36 for NA
Page F2-35 for Turbo

If you look at the pictures, there are 2 tick marks for using the adjusting screw to set the thing with the engine cold. If the cam separates, as it should, once the engine is warm, you might have something else holding the throttle plate open just a crack, or you might have a vacuum leak.

I don't know if this is the same problem on your car, but here might be something similar. On my car, I have a problem of the top throttle plate not closing all the way because the throttle return spring is weak. Haven't heard of this problem elsewhere, and the mods might call me dumb, but at fully warmed up, the throttle plate returns to rest about .010-.015" away from the idle set screw. The idle hangs high and sometimes bounces. Not harmful, just drives me nuts. If I take a long screwdriver and push the plate back the rest of the way, it goes where it is supposed to. My return spring is just out of tension at the end of it's travel. I have tried to order the Mazda set of throttle springs and they are apparently made of fairy dust as the kit cannot be found on this planet. Gonna turn a mandrel in the lathe and try to make my own.
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Old 05-19-17, 02:43 PM
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Note:The TB is an S4.
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Old 05-19-17, 07:38 PM
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Works the same.

S4 pages
4A-56
4B-62
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Old 05-19-17, 11:47 PM
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Good reply---thanks! I'm going to take the TB off, so I can clearly see the marks on the cam and better understand what's going on.
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Old 05-20-17, 09:16 AM
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As far as adjustment, the marks are just approximations. If it's anywhere close, and the thermowax still works, it will rotate that cam clear out of the way. If you don't want to have it hot while you're working on it, you can easily remove the cam from the system so the plunger is separated mechanically from the throttle shaft. Then you can check to see what is holding your throttle open. If that was what was doing it, just put it back on and adjust and you should be fine.
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Old 05-20-17, 09:11 PM
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I took the TB off and checked everything on it according to the FS2. I put the TB back on and managed to get a pretty good idle. I still have to play with the fast idle to get it to where I want. But at least it's fast idling and then coming down to idle. Anyway, right now the idle is fluctuating between 800-900 rpm's. I can live with that. But what is driving me nuts now are two things: When I push in the clutch to come to a stop, the rpm's drop drastically. It used to stall on me, but now at least it's not stalling. Secondly, when on very light throttle-----I mean like barely touching the gas pedal, it will want to buck a little. My thoughts are that to help with problem 1, I probably should, first, change the spark plugs. If that doesn't solve it, I'm wondering if I can bump the throttle plates open a hair (that set screw with an 8mm nut that's on top of TB) to see if that helps with the rpm's dropping so much. Of course I know that I may have to reset the TPS--no problem. For problem 2, I guess I'll just have to play with the TPS?

I read somewhere (can't remember where) that the TPS is best set on the lower kohm side like around 1,000. That's where it is now when fully warmed (1,050). I know that if setting the TPS with the two light bulbs, most guys set it somewhere in the middle between the low and high kohm range. I'm just thinking that even though my TPS is set within range, I may want to play with it and perhaps set it somewhere in the middle or closer to the high range and to see if that helps with problem 2.

Lastly, I noticed that in order for me to achieve a somewhat steady and smooth idle, I had to set the lean-rich set screw all the way to rich. Any thoughts on this?

Thanks!
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Old 05-21-17, 09:26 AM
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Sounds like a vacuum leak.
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Old 05-21-17, 07:34 PM
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Originally Posted by Acesanugal View Post
Sounds like a vacuum leak.
Certainly wouldn't hurt to check that. Thanks
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