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a) Check throttle cable. Make sure it's not tight and holding throttle open. You can just remove it while testing the idle too.
b) Check the thermowax and the fast idle cam. Possible the throttle plates are being held open.
What you can do is warm up the car to operating temperature. So that the thermowax has fully extended. Then shut the car off, take off the intake snorkle and see if you can see a gap between the throttle plates and throttle body. On mine it is pretty much closed/hair line gap when hot. Do this somewhat quick so that the thermowax doesn't begin to contract. FYI when the car is cold, this gap will be larger due to the thermowax. This is why when the car is cold the idle is high. Once the car warms up, the cam moves and plate closes and idle goes down.
You can kind of check it with the car off too. But if your thermowax isn't extending properly this way won't identify your problem. Car cold. Take intake snorkle off so the primary throttle plate is visable. With a flat head screw driver press down on the bracket linkage between the fast idle cam and thermowax (Doesn't have to be a flat head, as long as you can press down on a metal bracket). Press down and see if the throttle plates move from being slightly open to pretty much fully closed.
You would press down with flat head where red arrow is.
If cam roller (red circle) isn't moving to position shown when your car is hot, your idle will be high.
c) hmm other things I can think of but might not be the case but something to check.
- BAC letting too much air past. But from what I read when these are stick these stay CLOSED and would cause low idle. NA S4 BAC isn't really adjustable and shouldn't be touched (ask me how I know lol) But on the front there is a spot where a hex fits and this can control how much air the BAC lets in per pulse. If yours is factory though, I would not touch it at all. But never know if the past owner fiddled with it. If there's a little blue thread locker and plug is somewhat flush with the housing it should be factory setting still. If this plug is backed out (lefty loose-y), your idle will be high.
- Clutch switch. I know when you press down on the clutch the idle goes up. I think the switch that's triggered by the clutch pedal arm is the one that tells the ECU *clutch down raise idle via BAC*. I've read of people's springs breaking in the switch and replacing it with a ballpoint pen spring. But if the spring is broken, I think the car would always see the clutch pedal down and not raise idle. Does your idle increase if you press down on clutch? Your idle might already be too high that you wont see a change. So I wouldn't dig into this too much.
a) Check throttle cable. Make sure it's not tight and holding throttle open. You can just remove it while testing the idle too.
b) Check the thermowax and the fast idle cam. Possible the throttle plates are being held open.
What you can do is warm up the car to operating temperature. So that the thermowax has fully extended. Then shut the car off, take off the intake snorkle and see if you can see a gap between the throttle plates and throttle body. On mine it is pretty much closed/hair line gap when hot. Do this somewhat quick so that the thermowax doesn't begin to contract. FYI when the car is cold, this gap will be larger due to the thermowax. This is why when the car is cold the idle is high. Once the car warms up, the cam moves and plate closes and idle goes down.
You can kind of check it with the car off too. But if your thermowax isn't extending properly this way won't identify your problem. Car cold. Take intake snorkle off so the primary throttle plate is visable. With a flat head screw driver press down on the bracket linkage between the fast idle cam and thermowax (Doesn't have to be a flat head, as long as you can press down on a metal bracket). Press down and see if the throttle plates move from being slightly open to pretty much fully closed.
You would press down with flat head where red arrow is.
If cam roller (red circle) isn't moving to position shown when your car is hot, your idle will be high.
c) hmm other things I can think of but might not be the case but something to check.
- BAC letting too much air past. But from what I read when these are stick these stay CLOSED and would cause low idle. NA S4 BAC isn't really adjustable and shouldn't be touched (ask me how I know lol) But on the front there is a spot where a hex fits and this can control how much air the BAC lets in per pulse. If yours is factory though, I would not touch it at all. But never know if the past owner fiddled with it. If there's a little blue thread locker and plug is somewhat flush with the housing it should be factory setting still. If this plug is backed out (lefty loose-y), your idle will be high.
- Clutch switch. I know when you press down on the clutch the idle goes up. I think the switch that's triggered by the clutch pedal arm is the one that tells the ECU *clutch down raise idle via BAC*. I've read of people's springs breaking in the switch and replacing it with a ballpoint pen spring. But if the spring is broken, I think the car would always see the clutch pedal down and not raise idle. Does your idle increase if you press down on clutch? Your idle might already be too high that you wont see a change. So I wouldn't dig into this too much.
I may give that a shot. I've had the intake off with the car dead cold before, and the throttle blades aren't propped open at all. Maybe a sign that it isn't functioning?
Also, is there a downside to deleting the thermowax on an S4 NA. I saw the writeup on fc3spro, but it seems like they imply to do it on a turbo model.
For reference, here is a video of my idle hunting. It will bounce then hold for a few seconds before bouncing again. My idle is consistently around 1200 to 1500.
Oh if the plate is closed when cold, then the thermowax/fast idle cam shouldn't be causing the high idle.
But yes it should be slightly open when cold, so something is off.
Downside to removing thermowax on NA S4... all I can think is you might have to hold the throttle down a bit while the car warms up. But if you're saying the plates are closed with the engine cold, removing the thermowax wont really change anything for you.
Because the way the thermowax functions...
Engine cold -> thermowax is contracted/resting state -> throttle plate held open -> higher idle
Engine hot -> thermowax expands -> throttle plate is able to close -> lower idle
Oh if the plate is closed when cold, then the thermowax/fast idle cam shouldn't be causing the high idle.
But yes it should be slightly open when cold, so something is off.
Downside to removing thermowax on NA S4... all I can think is you might have to hold the throttle down a bit while the car warms up. But if you're saying the plates are closed with the engine cold, removing the thermowax wont really change anything for you.
Because the way the thermowax functions...
Engine cold -> thermowax is contracted/resting state -> throttle plate held open -> higher idle
Engine hot -> thermowax expands -> throttle plate is able to close -> lower idle
Understood. So, I guess my next question would be:
what could be causing my high idle?
Intake was recently rebuilt. All vac lines are new.
EGR deleted
Sub zero deleted
EGR solenoid deleted
ACV is still intact along with it's associated solenoids on the rats nest.
The adjustable FPR I have installed uses the OEM FPR vaccum reference. The FPR solenoid is also still intact. Could this cause fluctuations in my fuel pressure?
Is there a downside to deleting ACV? In S4's I know the 5/6 port actuators are controlled by back pressure from the exhaust. So, am I losing anything by ditching the ACV all together?
Another update here, with some pictures and additional questions.
So I decided to pull the throttle body off and take a look at everything attached to it just to see if it was working.
First thing I noticed: my coolant level keeps going down. Only reason I bring this up is because I have no external leaks that are visible, and I doubt I've popped a coolant seal. What else could be wrong?
As for the throttle body, first thing I did was test the double throttle actuator. This guy:
I used a hand vaccum pump to pull vaccum on it, and I couldn't get any pressure to register on the gauge. So this is shot.
Next thing I notice is the thermovalve. My car is M/T, but it appears I have the thermovalve for an A/T car. Would this affect anything?
Lastly, I checked the thermowax itself. Appears to have been replaced at some point, but the fast idle cam does NOT work. It's locked in place, and won't disengage from the green pin. Any suggestions on how to fix this? I've soaked it in PB blast and tapped on it with a mallet, and still no movement.
I believe this is what has been causing my elevated idle, but from my understanding, the fast idle cam should prop the throttle blades open slightly at idle. But mine are completely shut. Any thoughts??
I don't know too much about removing the ACV. I live in CA so I try to keep everything on because of smog requirements. I wish I could take stuff off though.
Double throttle is okay if it's not working, just make sure to cap off the nipple/line coming from the thermovalve. If you had vacuum lines running to the double throttle before, possible it might of been causing a vacuum leak.
For thermovalve if your double throttle actuator is not working, I think you can just cap it off. I believe it's only function is to provide vacuum for the double throttle actuator. If it's from an AT, just cap and run lines to match the MT version per FSM.
Your fast idle cam. Yah that's too far past. It should be riding the cam. As shown below. A little hard to tell from your pic/orientation, but I think you're way past the 0°C mark in pic below. Is it stuck stuck? like the spring is frozen? Or just stuck on other the other linkages. If it's just stuck on other linkages/iteself, you should be able to press down with your thumb on the two flat heads show on left and right in your pic and it should let you spring the plates back and forth.
If you can take another pic of the thermowax and fast idle cam from the side that would be good.
12-16-21, 11:34 AM
