z06sicz

2007 Z06 cam 242/246 .605/.606 on 114. Heads are un-milled with a valve job. Halltech CAI, with MSD intake. 1-7/8" headers, no cats to stock bimode exhaust.

Had the car tuned, and I'm getting surge and stall intermittently, worse when cold started. After complete warm up, a rev and release will drop below 800 rpm, and bounce back to 975.

When I turn the car off warm and restart, it will start and hold idle. When I put it in gear, and go to drive off it will run until I go to neutral at the first stop. The idle drops to the point will it will almost stall and just keeps trying to stabilize. Most time this will results in a stall. When I restart the car it cranks for a few seconds and starts hard, but then seems to run as described in the first paragraph.

The tuner says it's not his tune, that there is a problem with the car. He refuses to look at it.

Here is the correspondence:

Hi Joe, I was in about a month ago to have Mike tune my corvette. It runs awesome at WOT, but I'm having some issues. I wanted to put some miles and drive cycles on it before contacting you to see if it smooths out, but it has not.
I'm getting a lot of surging until the car is completely up to operating temperature. It will hunt for idle and stall at times. It gets better when completely warm but still will want to stall once in a while. I'm also getting some bucking in the lower rpm's (1500-2200) at cruise.
Can you bounce this off Mike for his opinion?
Thanks Jeff Swoyer


Will do jeff.



Hi jeff.

I did ask mike about your question and he did respond.


Here is what he said to do:

His car had a pretty bad fuel trim imbalance between banks. Normally it's 2 percent or so. His was 16 percent according to the logs. I'd bet whatever is causing it is getting worse. I did show him this. Suggest going back to the LS6 intake, change O2 sensors, injectors, etc. Once the imbalance is fixed, come back for a retune.

Mike

So, something is affecting your fuel trims and tuning around it is not the answer apparently.

If you want to discuss, give me a call. What mods exactly do you have on your car?

Joe



1. How much is a retune?

2. Shouldn't the logs show a value for the 02's pointing toward a bank for the sensor in question?

3. Same for the injectors?

4. A ls6 intake doesn't even fit a ls7 as the intake ports are not cathedral???

5. Will Mike at least have a look at the current tune and confirm it's the best he can do?
Jeff

This is where it ended and I have not heard back from them in over a month.


Any advice on what could be the issue? I'd like to correct it IF it is the car, and take it to another shop to get tuned if needed.

z06sicz

Here is the dyno sheet

Must_Have_Z

First sign of trouble is when the tuner says the issue "is not with his tune." That's ignorant and not helpful. It could definitely be a mechanical issue or something with a part that was installed, but unless something is blatantly and obviously wrong that you can see/feel/touch, then it's a problem with the tune. I have a cam with similar specs as yours and there's very very little surge if I'm in too tall of a gear and going really slow. No issues in neutral or coming to a stop.

I had similar symptoms as you when I had work done on my old C5 Z06. The car would not idle well, would stall coming to stop signs (coasting and pushing in clutch), etc. It was awful. Undriveable. My tuner was nice enough and kept tweaking and taking a look at it. After months of this, I decided to visually inspect as much as I could with the parts that were replaced. Everything looked great except when I checked my intake manifold the vacuum line at the back was NOT HOOKED UP. Yikes! That was the cause of all our issues. A whole bunch of unmetered air was getting into the engine and threw the tune way off.

Take a look at your air intake connection, the coupler, and all of the lines coming into and going out of your intake manifold, sump tank and valve covers. Look for cracked, broken or missing connections at these points. You may get lucky and find that it's one of these.

If you don't, then you're back to the tune and the tuner who says it's not his fault. Good luck. (A "retune" will cost you the full tuning price if you go to a different tuner who needs to unlock your computer.)

All Stock Ls2

Unmetered air? Check for vacuum leaks past the MAF I've found this to be the issue in the past but not too often. Also, while you're at it check/clean your throttle body I'm not saying that's the issue t sounds like a vacuum leak to me unless it is the fuel trim that's messed up but you'd be surprised what a HUGE difference a clean throttle body makes.. my car is fully built (literally) and I had issues stalling/surging/holding idle/dropping idle and it was a nasty throttle body. Best of luck to you and yours brother

z06sicz

Thanks guys.

The car only has 9,000 miles.
Checked all lines coming and going to the intake and throttle body. Everything looks good.
Checked all wires, and plugs. They all check out fine.
Pulled the CAI, and throttle body had a slight oil mist inside it. Cleaned everything up in there. Pulled the MAF sensor and it looks like some oil residue from the filter was on it. Gave the MAF a good spray down with electrical parts cleaner, especially the resistors.

Put it all back together double checking all connections for seal.
Started the car and didn't touch the throttle. Brought it up to operating temp and turned if off for a relearn.

Fired it back up and gave it some revs. Everything seemed to settle.
02's are cycling fine, and LTFT's are settled about -2 to -3

Took the car out for some miles, and performed an ignition cycle while fully warm.
ALL seems much better.
The car even tolerates 1500 rpms in sixth gear!

Only thing I can think is the oil from the filter was sucked in on the dyno runs creating the surge, issues.
Hope all keeps going well.
No more embarrassing fuel up's!

Thanks to everyone for there input.
These forums can save your sanity!

Still disappointing the tuner didn't confirm things on his side, but live and learn. I'll take my money elsewhere next time.

All Stock Ls2

Ironically enough I cleaned a friends MAF and throttle body today and fixed his idling issue on a 2011 Ford Escape. The issue with the MAF is that's it's VERY sensitive and any oil from the filter or dirt that gets past the filter will not allow it to meter the air that's coming through and you'll get that issue and a dirty throttle body won't allow the proper amount of air to come through to keep it idling steadily which is why those two are my go-to checked when dealing with sporadic idling. Glad we were able to help you brother if you have other issues post it on the forums or feel free to message me. Take care bud