Problems with tuning file, unintended acceleration!

[LS XJ]

OK, so I thought I had the SD tuning file correct. I'm trying to get my VE done with my WB but the SD tune is not going well.

Right after writing the SD tune the truck runs OK, not real smooth but plenty driveable. The problem first happened about 40 minutes in. It suddenly began accelerating on its own!

I would back off the gas to reduce my road speed but the truck would keep on trucking! The scanner showed a TPS of 8% even though I had my foot off the gas. As I brought the truck down to a stop the engine was still trying revving. I would have to slip it into neutral so I could stop. The TPS remained at 8% in neutral as I coasted to a stop, RPM was about 1,100. About 3 seconds after coming to a complete stop the RPM dropped to 550, the commanded idle. So I put it into gear, no problems, still idling fine. I take my foot off the brake and it slowly begins to roll, as an automatic should, but, when it hits 3 kph the throttle suddenly opens to 8% again and the truck surges forward. Very unnerving when you are maneuvering near obstacles!

So I uploaded my "best so far" tune. It began doing the same things, but not as intensely. After about 10 minutes the misbehavior was hardly noticeable. After another 10 minutes it drove as it should.
So this morning I uploaded the "SD" file again, and it's started all over again, I can't drive it like this, not safe.

Now a little history. When I was creating the SD tuning file I neglected to zero out the MAF. When I drove it then, about 40 minutes into the drive and it would suddenly loose power and struggle to idle, then no throttle response. My WD would go out of range lean at that moment. I had to upload my "best so far" tune, then it was OK.

It appears that the PCM is trying to compensate for something as the drive goes. If it is running real lean and "might" stall, maybe it is trying to prevent a stall.

I've attached both my "normal" tune that runs smooth and drives great, and the SD tune that I am trying to use but is misbehaving.

Your thoughts? I need to have a safe to drive SD tuning file.

Thanks

[Area47]

set all of the airflow tables back to stock. {idle>airflow} try again.

[LS XJ]

I didn't touch any idle stuff except the idle speed.

I copied the stock VE to the SD tuning file. Now, I DID have an exhaust leak on the right bank, about 3" before the factory O2. My WB is on the same side back 42" from the head. I've fixed that and drove it again. It still wanted to take off when rolling very slow, but that calmed down and went away completely in about 10 minutes of driving.

It is also possible that when I did the previous SD drive that I didn't turn off LTFT and left it in Closed Loop. Is it possible that the PCM was trying to compensate by boosting the idle speed?

So this time I've driven about an hour with no issues. Seems to be OK now. I blame operator error.

Thanks for the help.

[LS XJ]

So after my last drive, posted above, I had to make a run to the store without the laptop, hence I did not force open loop or turn off LTFT.
It started out good but then the idle was elevated while coming to a stop, but not near as bad as before, and it didn't surge ahead when I hit the 3 kph mark. So I think the PCM WAS making adjustments before.

Learned something today.

[compsystems66]

I checked your tune and compared it with a stock 03 2500 HD truck, your throttle scale in the tune is not stock, and may be the cause of your issue.

Engine - Airflow - Electronic throttle - Desired Throttle Area

Both normal and alternate are not stock.


Also, electronic throttle bodys are known to stick sometimes. Cleaning it would also be a good idea.

[LS XJ]

I didn't touch anything to do with throttle. I compared my current tune and the stock tune I pulled off the truck when I began and it is the same.

I may have forgotten to force open loop and turn off LTFT learn when I began my drive. I have since done another drive and the problem has disappeared.

[5FDP]

You already have closed loop and STFT/LTFT disabled in the tune you are using, you should not have to force anything with the scanner.

[LS XJ]

Well it's not gone!

I've logged a couple of minutes. I can't say if it does it cold as I've been tuning for the last couple of weeks and I don't usually drive off until it's near operating temp.

What it does
It idles about 580, target idle is 550
I put it in gear, idle speed is the same.
I take my foot off the brake and it slowly rolls out.
Within a few seconds the TPS starts climbing, until it reaches 7% on level ground. If I poke the throttle and take my foot away the TPS drops to 7%. If I come to a stop, the truck is pulling as I stand on the brakes to stop it. A few seconds after I've stopped the TPS drops to 1%.

7% doesn't sound like much, but that's 70kph on level ground. Sometimes I put it in gear, don't touch the throttle and the TPS jumps to 7% after a few seconds, then a couple of seconds later it drops to 1%.

It likes 7%

In the attached log I only touched the throttle for a few seconds @ 50.182, then released it at 54.975 Notice how it stays at 7% while I'm coasting. A short burst @ 1:14:958, then coasting at 9-10% until I stop.

The engine is a swap from a 2003 3/4 HD Chevy 2wd. I didn't drive the truck, but it was running ok for the little bit I moved it. I've been driving around with the attached SD tune for a few hundred kms with no problems. This began a few days ago. I really need to fix this! I'm having to slip it into neutral to slow down. It doesn't show on this scan but the TPS has jumped to7% suddenly on occasion as soon as the VSS indicates 3 kph. This is very dis-concerning while maneuvering near cars or people. I had a pedestrian step into the street mid block and I slowed quickly to let him pass and I waved him across. My road speed crept up to 3 kph when he was in front of me and the truck jumped forward.

I've attached the tuning file I've been driving all this time, as well as the stock file from the truck. I haven't touched anything in the idle section except for the target idle. I did put the idle speed back to stock, no difference. I flashed the stock tune back in the PCM and no change.

I'm wondering if the PCM has "adapted" to something as a result of the tuning file. I've been driving with the MAF zeroed out for most of this time. My current fuel trims are still about 4-5% positive. I tried enabling the MAF, with the stock tune and it ran soooo lean in the first few seconds that I didn't trust it on the road in traffic.

I've done some searching on this forum and everywhere else and didn't find anything close. I found something called "Throttle Cracker" but not enough info that I could make sense of it.
One thing I have noticed in the last couple of days, don't know it it's relevant, but when I pull the transmission down to 3rd while coasting in 4th, the throttle "blips" as it downshifts, like I've read about on the newer Camaros. I didn't notice this in the beginning, maybe I wasn't as focused on the RPM behavior at the time.

Thanks to anyone who takes the time to look at the files and offer some advice.

[LS XJ]

Well I've found something, just before I shut the computer down and head off to bed.

Throttle cracker, maybe??? I found a video, I'm going to try this tomorrow and report back.
https://www.youtube.com/watch?v=MxnnFDpy2-4

[LS XJ]

Waaahooo fixed!

It was the throttle cracker that was causing the throttle to "hang" when coasting and when stopping.

[850sc300]

So what was the exact issue I just started having the same issue all the sudden.