ULTIMATEORANGESS

iTrader: (4)

i feel your pain. my tuner has been fighting something like this with my car only worse for quite some time.

senicalj4579

iTrader: (41)

Yep we did and im glad you remember.
Yea, car has done this since day one. I took the car back once. I was told it acts like the best car ever tuned and theres no surging/stalling. I pretty much gave up after the 2nd time I picked it up and accepted the car. But the other day I caught it with a slight surge stopped in traffic so that triggered my curiosity again as to why it does what it does at times. I mean obviously im not imagining it...its showing how it surges and dies in the vid.
So now im just trying to figure it out myself

According to the info I gave you what else should I be seeing/looking for as far as TPS, LTFTs, ect... and how do I read IAC counts?

Thanks for all the help.

RPM WS6

iTrader: (3)

Those percentages sound perfectly normal. However, looking at the factory service manual, the diagnostics matrix and references are all in voltage readings. My scanner (AutoTap + laptop) happens to show both values (percentage and voltage), but if yours doesn't show voltage you can always get those readings manually with a DMM (digital multi-meter) by probing the harness. It sounds like the TPS is working ok though, and that pending DTC may have somehow been triggered as a result of unplugging/plugging the TPS. Wouldn't hurt to keep an eye on it though, and see if the pending DTC ever returns. Perhaps it has tripped before, but never twice in consecutive cycles which would be necessary for it (or any Type B) to trigger a MIL.

It's possibile for IAC values to actually be -0-, but that's not a good thing if that reading is correct. It would indicate that the engine is somehow getting enough air to idle (either via a vacuum leak or large enough gap between the throttle plate and throttle body bore [or enlarged throttle plate hole]) without any help from the IAC. This is an issue because it means that the PCM has lost control over idle speed regulation, since it has already done all it can do to reduce idle speed by closing the IAC entirely (0 = closed).

BUT, I don't think that's the case here. Your vid and description of the issue are not consistant with a closed IAC and idle speed that is unregulated. You would have cruise control effect (car maintaining normal cruising speed even after you release the gas pedal) and idle hang (idle staying excessively high after a free rev, not wanting to come back down). My guess is that the -0- reading is erroneous, but I don't know why. My scanner has always shown this value without a problem. I wish I knew how to get your scanner to show this value, because it might be helpful to see it.

It's good if the LTFTs are staying within 3% of each other and always negative. That's generally ideal, and what any tuner should shoot for. If you are seeing some instances where the split is large, you might want to see if it's always happening in the same FTC (fuel trim cell). Not sure if your scanner shows this value, but if the large split is always and only happening the same cells, then it might help point you and/or your tuner in a specific direction.

Usually fuel trims would be highly elevated (and positive) if there was a vacuum leak, but if the leak was present during the tune then it's possibile that it may have been accounted for in the fueling portion of the tune, thus the trims are negative even with a leak (I remember once seeing an H/C car that had been tuned with the PCV line unknowingly disconnected, and when I plugged the line back in the car actually ran worse since it had been tuned with this leak.)

My gut feeling is that the issue still lies somewhere in the tuning. If the surging/stalling can be produced as easily as you did in that video, then your tuner should also have been able to see it. Unless of course the issue is gets better or worse in certain weather conditions, in which case it may not have been present when the tuning was done and also rechecked.

Some degree of idle surge or idle instability under certain conditions can be expected with the combo of aftermarket parts that you have, but this is more extreme than I would expect if everything were in its best possibile state.

senicalj4579

iTrader: (41)

I think I might need to bring it to someone that knows what they are looking at and will scan it to see what might be going on. Iv been told im picky about my car but when this thing surges/stalls at times like it does im not so sure that anyone would except it as normal

RPM WS6

iTrader: (3)

I wouldn't worry too much about that minor change in percentage. Over the many scan logs I have done of even my current stock cars, I've seen percentages at idle show up as 0% or 0.4% just like yours, as well as 99.6% or 100% at WOT. This was the case on cars that were not having surging or stalling issues, so I don't think it's any indication of an actual problem.

The more you scan stuff, the more you'll get a feeling of what is "normal" for your particular application.

Some of that might be in the tune, or due to the hole size in the TB blade (if bigger than stock), or due to the setting of the stop screw for the TB blade. Since it's not an original stock TB, I'd only be guessing at whether or not they are set the same as factory.

Again though, this is where it would be helpful to see an IAC value that we know is correct. A stock car with a stock TB and stock idle speed would normally be in the ~10-30 range, depending on load and temp. If it really is 0, then the PCM is not in complete control of the idle speed and that could certainly lead to idle instability.

For a stock car with stock tuning, the numbers will normally be positive but still very close from bank to bank. When the numbers are positive (adding fuel) they will lock at that value when you go WOT; when they are negative they will lock at 0% at WOT. Part of a good custom tune is to try and get the LTFTs to always be negative at cruise, and therefore locked at 0% at WOT, thus keeping WOT A/F consistant and ideal as per the custom tune.

Large splits from bank to bank could indicate an issue with an O2 sensor or a vacuum leak - especially a leak that's having a greater effect on the bank that is more elevated.

If your scanner allows you to see FTCs, then you can look for patterns among the splits, seeing if it's consistantly worse in a certain group of fuel trim cells.

While some degree of instability is certainly going to be normal for a combo such as yours, I think it should be better than it is. I think more time needs to be spent on a street tune for driveability. It's always possibile that this condition could be caused or exaggerated by a small leak or a sensor that is borderline, but I really think some additional street tuning would go a long way to clean up some of the issues.

senicalj4579

iTrader: (41)

I found this http://www.hptuners.com/forum/showthread.php?t=39918 and it sounds exactly like my car.

senicalj4579

iTrader: (41)

Ok I have a couple guys saying they are able to read fluctuations on their aeroforce gauges. Mine must be really reading 0

RPM WS6

iTrader: (3)

I read though this thread, and if your IAC counts are truly 0, then you might in fact be suffering from a similar problem as what is outlined in that thread.

I wonder if someone has opened your TB blade beyond the stock setting? This is where it would be nice to see the TPS voltage at idle (I just looked at a scan file of my stock '02 car and the idle TPS voltage is 0.5v.) This would explain why your engine is able to hold an idle without any help from the IAC, assuming the 0 reading is correct. Under these conditions, the PCM won't have the ability to maintain a constant idle speed in response to changes in load and weather.

If so, it's still looking like more time needs to be spent on idle tuning.

And for best overall power, those LTFTs should be staying negative at cruise and ideally not be split by consistantly large amounts.

It's still possibile that a small vacuum leak could be present, allowing in extra air that causes the PCM to shut the IAC in an effort to maintain commanded idle speed. That could also be one explaination for some of the LTFT elevations and splits that you're seeing.

LS6427

iTrader: (2)

I know this has been posted to death.....but never rule out failing 02 sensor(s).

They can make all kinds of thing look like the problem. Get a scan to see if they are switching properly.

.

senicalj4579

iTrader: (41)

They both are switching great in closed loop

Im going to close the blade today and see if it triggers some kind of IAC fluctuation.

Also I will try to return this stupid Acron scan tool that dosent read IAC counts. Wasted 250! What could I get to scan everything I need in a cheaper price? EFI Live scan only looks great but its 500. Any advice on a cheap scan tool?

RPM WS6

iTrader: (3)

Just for your own reference, the stock setting for the TB blade screw is to have the blade open just enough to prevent it from sticking in the bore when shut. TPS voltage should be about 0.5v or very close to that (which can also be seen on a DMM if the scanner doesn't show this value).

You might be able to find something used. I'm currently using AutoTap software and cable that's over a decade old, but it still works great and tells me everything I need to know. The laptop I'm using it on is from about 1997! The newer scan software can do lots of fancy things, but for my purposes I've found that the old stuff still works just fine.

senicalj4579

iTrader: (41)

Well guys just to update I installed new TPS+IAC and no change. Oh well I guess i'm done throwing $ at it.

RPM WS6

iTrader: (3)

Too bad it wasn't something simple like this. Sometimes you get lucky, but not in this case. Sorry to hear Joe.

SE-R Spec

iTrader: (2)

im having trouble with this on a LSx swapped MCSS. any update?

senicalj4579

iTrader: (41)

No updates sorry. I'v just been enjoying the car as is for now. The issue only shows its ugly head in reverse or coming out of my uphill driveway. Other than that the car runs great

bbarr43

Hey, did you ever resolve this issue? I'm having very similar issues after cam/head swap after tune. Car bucks and surges, goes up to 1500 - 2000 RPMs and hangs for a few secs, then drops. Most noticeable problem is car is surging, stalling w/ AC on. Replaced front O2 sensors with Bosch 13111s and removed codes. Performance seems progressively worse now. After initial tune and replacing O2s, car was hitting 390 HP, lately it's only around 288 HP (Using Torque app). I know that's inaccurate, but 100 HP loss? Check gauges will come on randomly with fuel gauge drop, sometimes light stays on with all gauges fine??? Random performance problem all around, sometimes it's powerful, sometimes it seems choked, not firing on all cylinders. Prior to tune, once I went WOT and car died at about 80 MPH. Also, I can recreate this same problem religiously every day. Upon first cold start, car will start fine w/ AC on, no idle/surging/stalling issues whatsoever. Upon second start, however, it will nearly always stall thereafter for rest of day w/ AC randomly. Question: Have you ruled out a bad PCM? Did you buy A/C Delco IAC/TPS? Any advice is helpful, I'm pulling hair out.

senicalj4579

iTrader: (41)

Yes problem was solved. I have had this oil leak for 2 years I have not been able to find until last week. It was the valve covers that were found to be leaking which in turn could have been the cause of a vacuum leak. All I can say is a new tune and new valve cover gaskets has this car running like it should of 2 years ago. I finally have my car back.