LS Idle question

[wblanton]

I have an LS motor from Turnkey. The O2 sensors are programmed out of it. Sometimes it idles about 1500rpm and every once in a while it will stick about 3000 after you get on it. I havent seen anywhere the wire is catching. Seems like the ECM is doing it not the throttle sticking but I am not sure. Any ideas?

[WS6]

Cable throttle body or drive by wire? The front O2s are still there correct?

[Shawn MacAnanny]

Vacuum leak? All the PCV and EGR lines intact? Unplug the computer and let it sit for a half hour then start it up and see if it re-learns the idle.

[wblanton]

It is a cable. I drove it tonight and the idle had dropped to about 1000 rpm and it only stuck once. Where do the front sensors mount? I know the rear sensors that go in the headers have been removed. I appreciate the info. Would disconnecting the battery do the same thing? My ECM is a little tough to get to.

[Shawn MacAnanny]

Haha yeah im sorry i meant disconnect the battery not the computer. Pcv runs from rear of driveside valve cover to front throttle body i believe.

[wblanton]

I appreciate the info.

[WS6]

what throttle body is on the engine? Your forward O2 sensors would be before any catalytic converters. The rears would be behind the cats. Your front ones should be in your headers or manifolds which ever you are running. I'm also assuming this engine has the factory style plastic intake manifold and factory style TB not a carb style manifold and TB? The engine can not run without forward O2 sensors. The PCM/ECM uses them to make the engine run. All EFI engines have O2 sensors.

Well, the only way it could run with out O2s would be in open loop which is what mode the PCM is in until the engine warms up. It would be very dumb for them to program a street car to run open loop all the time but technically it is possible. We will go on the basis that they still have closed loop operation in the programming for now.

[wblanton]

There are no o2 sensors on my car. The ones that mount in the headers were plugged. The sensors were programmed out. It is a stock throttle body and stock style composite (plastic) intake.

[dhutton]

If it is running open loop then I think it is using a lookup table to set fuel mixture, idle, timing etc. I remember that your car was dyno tuned, presumably the tuner set the parameters in the lookup table to get optimum open loop performance. There must be a set of operating conditions (as read in all the other engine sensors) in that lookup table that causes the idle to go to 3000 rpm.

Don

[wblanton]

I am going to make some phone calls on Monday. the engine was dyno tuned and the fuel/air ratio was set then. I am going to call the tuner and Turnkey. I havent talked to Turnkey myself to see how the setup should be. Long story short, the information i was given about the programming and sensors came from a not so reliable source that once did some work on my car prior to Prodigy that might explain some of this.

[dhutton]

If you post this question over on ls1tech.com you will probably get a lot more information.

Don

[WS6]

Ok stock TB pretty rules out it sticking some how. Some of the aftermarket units had sticking issues. I would call the tuner first and talk to them since they were the last to touch anything. Then call Turn Key and see what they sent out. Don't worry, this is an easy fix honestly so long as the headers were simply plugged with a screw in plug and not welded shut.

Just checked your build thread and see the headers are coated. If the bung holes were welded shut, you can put the bungs and subsequently O2 sensors into the exhaust system just after the headers. This will prevent the headers from having to be recoated. The only thing is the connection from header to exhaust pipe must be 100% sealed with no leaks for the O2s to function correctly.

[Mike Norris]

Hey All,

I had it on my dyno from Prodigy and have talked to Turnkey prior to the car coming to my shop. The system does not use oxygen sensors or a MAF and is a very basic speed density based system.

On the dyno with my wideband she was a bit lean cruising as well as at WOT so I added about 5lbs of fuel pressure and it seemed to be decent at that point considering there was not much else I could do. No way with the current setup to see what is going on with the PCM parameters or data.

For the sticking idle I did turn the idle screw as closed as I could make it until the blade began sticking when attemtping to open the throttle. I then opened her a bit to keep her from sticking and that would be about all I can do for a hanging idle without data or tuning capabilities.

Turnkey says we can send the ECU in to be unlocked as well as a cable is needed to purchase (decent big money) and then I can do some tuning. I would guess that the running airflow is the culprit. Not sure if tuning only is the issue, but a little data aquisition and tuning will see what is needed. Hope this info helps.

Mike Norris

[WS6]

Mike, what kind of system are they using? Glad to know it was in capable hands but this sounds like a really crappy management unit.

[wblanton]

thanks Mike for the info. Just drove the car and had no problems with it sticking. It seems to be an on again off again deal. Other than that the engine runs great. Plenty of power and great throttle response. I drove the car before Mike got it and it definitely has better response and seems to have a little more power. So basically I can deal with it or buy the cable and send the ECM in to be unlocked. Are there going to be any other benefits to having it unlocked and getting this cable?

[Mike Norris]

WS6,

I do not know about a crappy system, but Turnkey utilizes a Delphi MEFI 4 controller setup that is very basic.

wblanton,

I guess it really depends on how happy you are with the current state of the cars driveability and performance. I have not used this system so I am not sure how much I can do even with the proper cable, software and unlocked ECU. But there is only one way to find out

Just let me know.

Mike Norris

[protour_chevelle]

wow, no maf or 02 sensors. Sounds like fun to me. :S

[wblanton]

it is very drivable. When it sticks if I put a load on the engine, downshift and let the load pull the rpm's down it goes right back to running normal. If it isnt going to get worse it's not that big a deal. It also has a cool sound at normal idle and even shakes the hood a little, gives you more of a carbed sound at idle but the throttle response of FI. If it were an easy fix I would fix it.

[MastMotorsports]

If the system uses an Idle Air Control Sensor, it can sometimes stick causing the conditions that you are describing.

Hope this helps!