RPM slow runaway in 2nd gear

[ColPaul]

What defines the minimum RPM when not depressing the throttle pedal? In 2nd gear starting at about 1000 RPM, my dad's 5.3L with a 4L60 and pretty stock OS slowly creeps up in speed. The RPM and speed will slowly increase until he has to ride the brakes to keep the speed below 25 MPH. I assume that the idle table desired RPM have nothing to do with this as the truck is above 10 MPH. Is that correct? Is there some minimum airflow that the computer is commanding and pushing the rpm up to?

[1project2many]

There is a table that defines desired rpm in idle. It's possible the IAC is failing and cannot be retracted. It's also possible a component is leaking air around the throttle plates. If you have a laptop and cable you should be able to view desired RPM and the IAC counts. If desired rpm is lower than actual rpm and IAC counts are zero suspect IAC first then vacuum leak second.

[brian617]

Most likely Rolling/Moving Idle or Rolling Airflow

[ColPaul]

This is a 5.3L Vortec from a 2003 truck that has been transplanted into a 1991 S10. There is no IAC. The idle is fine as long as the truck is in park. Even in drive, the idle tracks to the desired idle table as long as the truck is stationary or even in 1st gear. Once I get into 2nd gear, the rpms start increasing. Data logging show that the TPS is opening up as the RPM increase, much above the desired idle table.

What controls the "idle" with no pedal commanded throttle and speed in the mid/high teens or low 20's? I assume there is a minimum airflow that is slowly increasing the throttle even though the pedal is not being touched.

[ColPaul]

Most likely Rolling/Moving Idle or Rolling Airflow
B4332 Rolling Idle RPM table, B4337 Rolling Idle High Correction, & B4336 Rolling Idle Low Correction are all zeros. Does that mean that there is nothing added to B4603 Desired Idle table for Rolling Idle?

B4333 Rolling Idle Disable Speed & B4334 Rolling Idle Enable Speed are both set to 256 mph

I attached the 1MB image bin file.

What switches the computer from idle rpm control to say OL or CL control?

[2xls1]

Throttle cracker table. Try changing every cell with a value over 1 to 1. This screen shot is looking at the file with HP Tuners.

[ColPaul]

Thanks for the suggestion. Most of the values in 1000 rpm were above 1 so, I reset them to 1. I didn't adjust the 1600 rpm column yet. I'm hoping that the computer will interpolate bewteen the 1000 rpm and 400 rpm column and that the engine will stay below 1000 rpm. Now, if I can just talk my dad into flashing the PCM without me there! If so, I'll let you know if that worked.

[2xls1]

The screen shot is from your bin. And that is not what I said to do.

[ColPaul]

I didn't realize the screenshot was from my bin, but that looks like it. I'm using TunerPro and PCMHammer as my tools. If my entire problem is keeping the RPM below 1000 in 2nd gear with my foot off the gas, how does changing the table outside of that range affect the results? I'm not trying to be argumentative, but I do want to learn. I thought that the computer interpolated between the 4 nearest data points to produce the desired target. For example, if I was running 800 RPM at 18mph, it would interpolate between 600-16, 600-20, 1000-16 and 1000-20 RPM-mph table points. Please help me understand how the 1600 rpm and higher table values affect the low RPM condition.

Attached is my suggestion (vs. yours) for the next table to try. May be a little while for we get a chance to test it.

[ColPaul]

I was able to talk my dad through uploading the new image to his PCM. I used 2xls1's suggestion to set all of the values >1 to 1. Dad will run the truck tomorrow. Fingers crossed that this fixes it. He did test that the original computer (OS 12579405) and the new one (posted above; 12587603 with some slight mods for fan and speedo) both produce the same runaway condition in 2nd gear. I think this is a new issue with the truck, so I am thinking a hardware problem if the both OS's produce the same result. He cleaned the MAF as well as ran the truck with the MAF disconnected. He can't log, although he does have an OBD adapter connected to his iPad and uses Auto Doctor or Car Scanner to read realtime parameters (standard OBD not enhanced PIDs).

[ColPaul]

Setting allow Throttle Cracker Table values >1 to 1 did not solve the problem. I set all the value to zero and also set B4311 - Throttle Cracker Activate Speed and B4312 - Throttle Cracker Deactivation Speed to zero. Dad just tested it and the truck now idles in 2nd gear at a stable low speed. Thank you, thank you, thank you 2xls1!

[2xls1]

I think you have some other problem that you are masking or as I call putting a band aid on to solve that problem doing that to those tables. I see you also really reduced the g/sec numbers quite a bit in the base running idle airflow tables from their stock values too. You shouldn't have to be doing that. At this point I would smoke test the intake and look for a vacuum leak downstream of the throttle body. It takes air getting in to make rpms go up. And I suspect you have air entering the intake tract somewhere after the throttle body.

[2xls1]

And where did you get that calibration. Checking the VIN in your bin with GM TIS2Web, there is not a single segment that matches what is correct for that VIN #.

[Fast355]

I think you have some other problem that you are masking or as I call putting a band aid on to solve that problem doing that to those tables. I see you also really reduced the g/sec numbers quite a bit in the base running idle airflow tables from their stock values too. You shouldn't have to be doing that. At this point I would smoke test the intake and look for a vacuum leak downstream of the throttle body. It takes air getting in to make rpms go up. And I suspect you have air entering the intake tract somewhere after the throttle body.

^^^The last truck I tuned that had "cruise control" had a leaking vacuum booster.

[ColPaul]

I got the bin from here, specifically http://www.gearhead-efi.com/Fuel-Injection/showthread.php?1515-2004-TunerPro-Bin-Files&p=20003&viewfull=1#post20003. The truck's previous owner prior to my dad transplanted the 5.3L into the 1991 S10. He told my dad it came from a 2005 truck, but it appears to be from a 2003 1500 Silverado according to the the VIN. So I used "04 Chevy 1500 4x2 LM7 12587603.bin" from the above URL. Would you suggest a different donor bin? It needs to be the 603 OS as that is the most common for the XDF values. I start reverse engineering the 618 and translating tables and parameters from the 603 since we were told the engine was from a 2005, which was false. However, I would rather stick with the 603 to be common with the TunerPro community.

You are correct about the base running idle table. I am very new to this and was trying to find why it was idling too high in 2nd gear. I'll reset those numbers while leaving the throttle cracker table zeroed and disabled.

I'll tell Dad about your suggestion for a vacuum leak check. I did log some parameters while the truck was exhibiting the 2nd gear rpm runaway. The TPS value is definitely increasing with the RPM.

[2xls1]

That explains why I cant find another 03 Silverado cal to compare your bin to. The most important thing I've found on swaps using blue/green PCMs is knowing what parts you have and not mixing up different year ETC throttle bodies/tac modules/pedals/year calibrations. Assuming this is still an ETC setup.

[ColPaul]

It is an ETC setup. I believe the TAC, pedal, etc. all came from the '03 donor Silverado. Thanks for the warning. We will try to keep everything but the OS an '03.