This is a dumb idle question but I have to ask

[Gstclipse69]

Hey guys, I know this is another DREADFUL idle question and I have racked my brain for hours now and I have yet to get any insight into my problem. The problem being simply I now have developed idle surge again. I say again, this is like the third time in my history with this car that I've had this issue.
I will start by saying I have looked and studied the vfaq time and time again and searched as much as I can.
I also do not have an ISC or an FIAV. I have a 1g throttle body with the bottom half completely blocked off for the sole purpose of not having any idle surge problems. I have a gm maf sensor in the upper intercooler pipe. I know the o2 sensor is working, I see it fluctuating in my ecmlink log. I do not have any boost leaks. The throttle cable is not too tight. I have ecmlink and I have the "simulate idle switch from tps" box checked.
I have avoided this problem for awhile but now I'm trying to dial in a setup and not having the car idle correctly is driving my crazy. Once I start the car, the idle isn't too jumpy, but once its warmed up its good and surging. Any insight or advice would be helpful. Thanks, Chris

 

[BrokenTsi]

Without any ecu control over your idle, this is going to get tricky. I never liked it when I've had to tune car without an ISC, but I've managed to get around it a few times.

Let's start with the basics. You said there are no boost leaks, so I'm going to take your word for it. However, a boost leak of any sort will cause a huge idle surge, even without an ISC. A friend of mine has the exact same setup you do.....1g throttlebody, no ISC...everything blocked off. It idle surged worst then any car I've ever seen. The problem was the intake manifold gasket.

I'm also going to assume that your 1g throttlebody is in good shape. Also, I'll have to assume that your ISC blockoff plate is secured and the gasket is good, and there are no leaks.

The reason your car idles good at first, is because it runs in open loop for a minute or two before going to closed loop and then it surges. The ECU is obviously trying to compensate for something.....hmmmmm

Sometimes, non IAC users will try to crank down the idle adjustment screw to keep their cars from stalling out. If its screwed in too far, it will idle surge. According to your TPSvolts, it looks as if maybe its screwed in a little bit..? Your TPS volts are .69, and it should be at .63.

While in closed loop, try these few tuning fixes in this order.

1. I see that your coasting FC offset is 190. I know the dsmlink wiki says to try an offset of 200, but that doesn't always work with every car. If the offset is too high, it will surge. Try to lower it and see if the changes go away.

from v3 help files: Target idle This is the RPM that the ECU will attempt to maintain via control of the ISC and ignition timing whenever the ECU sees a closed idle switch (or simulated idle switch), and the engine is at normal operating temperature.
When setting Target idle above 900 rpm, it's a good idea to raise the Coasting FC offset setting as well, typically setting the offset to Target idle minus 900. (yours is 190)

Coasting FC offset is used to raise the rpm above which fuel cut takes place when the idle switch is closed.# This setting is often changed to avoid fuel cut at light throttle with Target idle values above 900 rpm.

2. Timing also plays a role in idle control in our cars. Try to pull some timing out in the areas that your car idles at. Look at your timing DA table in the Direct Access part of v3. See that big variation between 1000 and 1250 RPM? Try picking some values that are closer together. If you track the datalog, you'll see that 10* is highlighted at 950rpm, but the 16* cell right next to it also affects the 10* cell. When it surges into the 16* cell, the 22* cell will also be used. I personally use 14* in all those cells at idle. Give it a shot. Lowering the timing at idle will help control your idle.

3. This is a last resort fix. Try to lock the car in open loop in the Misc tab. Did the idle surge go away? If it does, you can configure OpenLoopThreshholds in Direct Access to run open loop during idle only. It will switch back to closed loop during closed loop driving conditions so you can still tune your car for good fuel trims if you choose to. I have not had to do this on my car or any other car I've tuned, but like I said....its a last resort. Let me know if you get to this point, I'll go into it further if I need to.

a little more info.......

Its tough to see whats going on because of the surging, but your CombinedFT is a bit high. This can cause an issue in closed loop idle conditions because the ECU is making changes based on o2 feedback. Try to increase the injector deadtime a bit and see if it comes down a little.

 

[Gstclipse69]

Man, I really appreciate the reply. That gives me a lot to go off of. I just got off work so to start Im going to try another boost leak test and go from there. Thanks!

 

[BrokenTsi]

Do it up!

 

[Gstclipse69]

So the boost leak test went pretty well. I might have found a miniscual leak that I think is from the throttle body shaft seals. Thing is I just replaced the darn things like 2 years ago. Anyway, I changed the timing cells in the DA tables to 14 and I changed the coasting FC offset to like 60 I think. And it idles much better just by doing that. I added a bit of deadtime as well, so as of now I am very pleased. It idles a bit high but heck this is night and day from what it was yesterday. Thanks a lot man. I guess I'll just order another set of shaft seals and replace them. It'll give me a reason to take the throttle body off and clean it well and make sure my blockoff plate is good and sealed.