HELP HELP 427ci idle tuning..please

[tomulrich]

Darton block
C5 corvette ELECTRONIC THROTTLE CONTROL 1998
11.2:1 CR
FMS 250/256 113 hydraulic cam .666/.680 lift Jesel Adjustadle rockers
48lb injectors
FAST 90mm intake/90mm LS2 throttle body.
Auto
headers/ Haltech intake

My car is having severe surging, hard start, erratic idle. Mail order tune was from Vette Doctors, An attempt was made by Mike Norris. Then a mail order tune by Futral. I was told there were mechanical issues because my manifold pressure was 8/hg.

What has been done
1. LS6 manifold TB swap (better but not gone)
2. LS2 Throttle body (better but unstable idle especially when cooling fans turn on off????????)
3. Took intake and valve covers off all valve/springs etc in good order ...replaced all gaskets, even rope seal between FAST intake. Replaced MAP,
4. Compression test 185-200 (two cranks)
5. 3-4% leak down
6. AFR with wide band (apprx 14.0)
7. Timing at 22 degrees (have tried all different timing settings)
8. 3/16" hole in Throttle blade (even without hole no difference...not much change with hole)
9. Hours of searching on-line (many many instructions used to tune)....no significant changes.
10. Smoke test for vacuum leaks...none
11. Cam was degreed when put in (all OK)
12. I HAVE SPENT HOURS CHANGING PARAMETERS IN THE IDLE SECTION (HPtuners)
At this point I dont know what to do. I am not going to ship the car anywhere.........it was very expensive and came back the same way.

I am not sure what anybody here can do??????

I am ready to pull the motor.....sell car....etc

Tom Ulrich

I have thought off everything///please help

[tech]

Did you adjust IAC vs. Park Position and Idle Airflow vs ECT? I haven't worked on ETC cars tho.

[tomulrich]

yes.....I have....one of the first things I changed.......many changes to this parameter....no difference seen

ETC is different....no real IAC counts to look at just TPS %


Tom


What should "ETC desired position" show on scanner?? when I log this parameter shows 1% and never moves. Remeber I am running a LS2 TB.........is this different than ls1 (connector harness has built in TPS / ETC control)

[MNR-0]

I would try and find a stable idle point first and work back from there. Find what thec ar wants to idle at, don't work against it.

That said...

1. set your idle at 1000RPM
2. set your base idle spark advance to 20* (both tables)
3. set your TPS voltage to 0.47v with engine running
4. shift IAC position vs effective are across 1 cell
4. reset your TPS sensor by disconnecting the plug, turning ignition on, waiting for error code, turning off then plugging back in the TPS sensor
5. check LTFTs are negative at idle (-2 to -6 is OK) and adjust VE/MAF/IFRs appropriately
6. check for O2 oscillation (adjust gain values accordingly)
5. trim your idle trims
6. gauge the spark advance where the car car wants idle based off idle underspeed and overspeed corrections
7. reset your base spark advance accordingly
8. retrim your idle trims (returning to point 6 until the underspeed/overspeed corrections are no longer biased one way)

Now you have an idling baseline to begin bringing down the idle RPM and repeat steps 5-8.

It takes a while. But it works for me.

The theres the throttle follower for preventing stall conditions on decel. and DFCO RPM/MAP boundaries to prevent pig-rooting (surging at cruise).

You can try disabling Adaptive Idle Fuel Control tio help lessne the effects of hunting if your cam is that big or you aren't pulling enough vacuum at idle.

[CAT3]

Sorry for whoring, but....
MNR-0,

1) in step 6 you say check oscillation of O2's, and adjust gain values? Which of the many O2 PIDs do you use to check oscillation, what should it look like, and how do you adjust gain values?

2) and if you dont mind, could you email, or post here, a more step by step on the process #5-8 on adjusting Idle trims? I see the PIDs, but not sure what all needs to be where? Thanks

Charlie

[LS6DAVE]

I am ready to pull the motor.....sell car....etc

I know and still knowing how you feel.....I had/have very simular issues a while back in my Mod-nightmare. Since our setups are so much diferent, my input may be of no use to you. Through my nightmare I have come to know; it is a combination of smaller problems causing the thought to be single large problem. With that said, you can be for sure that the fast 90mm intake is still leaking!!!!!! I have had mine on and off to many times to mention. You need to check clearance bettween bottom of intake and valley cover-best way I found was to cut a piece of news paper to lay on the cover and then install the intake. If news paper can be removed without tearing, it has clearance. I had to mill my cover, it hit on 3 different-brands of intakes. This was about 30% of my my intake leak issues. I have found several other leak problems with the Fast intake and still don't have a 100% seal.

Have you upluged the MAF and started the car? You my see the fuel trims take a very large swing-probally lean-adjust these-probally will run pretty good. Beware, stay below 4000 rpm-will go lean above that. Try this first, if it appears to be as I discribed, then we maybe in the same boat. If not, these members on this forum are very sharp, and a good bunch of people too, there knowlage/experiance can help you.

Dave

[MNR-0]

Sorry for whoring, but....
MNR-0,

1) in step 6 you say check oscillation of O2's, and adjust gain values? Which of the many O2 PIDs do you use to check oscillation, what should it look like, and how do you adjust gain values?

2) and if you dont mind, could you email, or post here, a more step by step on the process #5-8 on adjusting Idle trims? I see the PIDs, but not sure what all needs to be where? Thanks

Charlie

Whore away!

Adjust the O2 Error gains both at idle and in motion so that your O2 sensors show happy swinging top to bottom. Too much gain and you overshoot the mark causing surging. Too little and rough idle.

Idle trimming has been discussed before. Use the search button. But...

Monitor your LTIT and STIT PIDs as well as your Base Running Airflow. The trims should be clsoe to zero for good ide airflow. If positive, add both the LTIT and STIT to your Base Runnign Airflow and vice versa. Leave it ide for 5 mins so the TRIMS settle. Enjoy the mystifying effects of O2 oscillation while you wait. :-*

[Billiumss]

Is this an all out drag car or street car? If it's a street car, your cam is way too big. I'd suggest a 240 244 116lsa cam for your auto.

I just tuned my friends 2002 Z06 427 LS2 with a 244 244 112 cam it it's barley streetable. I have his idle set at 1,000rpms.

Go with a smaller cam and most of your problems will go away.......

[V locity]

Bring this back to life...

How do you adjust the gains on the o2s for smooth oscillation?