2001 Blazer Surging idle after warm eng restart.

[gnnova]

I have a 2001 S-10 Blazer 4.3 with a 0411 PCM that I have been chasing an issue with after it sets off for 10 to 25 min then start it. The idle rpm will surge up and down for a minute or so, then smooth out. Also the idle will be smooth for the first few seconds. When scanned it was showing lean condition so I increased the after start enrichment as suggested in a earlier post. This has help but not cured the issue. The motor is stock except for a cam from a mid 90's 4.3, a 180 deg thermostat, #36 lb injectors for a later turbo, an opened up air box and an improved H-pipe/exhaust. I am running it in SD mode with the MAF disabled. I have performed the desired idle air procedure to get the IAC calibrated. Can someone look at my tune and scan to see if there is anything else to do?2001 Blazer added added to after start enrichment 4-18-23a.hpt2001 Blazer erratic idle after start 4-20-23a.hpl

[blindsquirrel]

Put the VE back to stock, in the 400-1600 RPM range. Just as a test.

[blindsquirrel]

Are you sure about what you've got in the Short Pulse Adder table? Looks strange. Messed-up injector data could cause this too but try the VE table first.

[blindsquirrel]

Downstream O2 sensors completely removed, or left plugged in but tied up out of the way as they must be with Gen 3 PCMs? There's no way to truly stop these from running the catalyst/post-O2 tests, need to have the rear sensors plugged in so it doesn't keep trying to run the tests that will never complete.

[gnnova]

Are you sure about what you've got in the Short Pulse Adder table? Looks strange. Messed-up injector data could cause this too but try the VE table first.

The Injector Short Pulse Adder was wrong. I missed it on AUS's spread sheet, it was a couple sheets back, when I put the data in. Shouldn't I make the injector data right and see if it corrects the issue before I change the VE?

[gnnova]

Downstream O2 sensors completely removed, or left plugged in but tied up out of the way as they must be with Gen 3 PCMs? There's no way to truly stop these from running the catalyst/post-O2 tests, need to have the rear sensors plugged in so it doesn't keep trying to run the tests that will never complete.

The after cat o2 is in place and connected up as in the stock config. The cat is gutted.

[gnnova]

Are you sure about what you've got in the Short Pulse Adder table? Looks strange. Messed-up injector data could cause this too but try the VE table first.

I changed the Short Pulse Adder first and that was no help as I think you suspected. I changed the VE table to as you suggested and that has helped alot but did not totally solve the issue. I attached the most recent scan that has the best idle with your suggestion of adjusting the VE table. Should I do the desired idle air calibration again?

2001 Blazer erratic idle after start 4-20-23d.hpl

[blindsquirrel]

Have you reverted the changes to after-start enrichment yet? Just thinking those changes may have somewhat masked the VE thing and now are hurting more than helping.

[gnnova]

Have you reverted the changes to after-start enrichment yet? Just thinking those changes may have somewhat masked the VE thing and now are hurting more than helping.

No I have not. I'll try that tomorrow. Thanks

[blindsquirrel]

After that, you need to fine-tune idle fueling, not so much base airflow/TPS/IAC stuff. Data collected while driving around really isn't what you need for adjusting VE in the idle regions. Doing that will lead you astray... hard starts, surging idle etc.

[gnnova]

After that, you need to fine-tune idle fueling, not so much base airflow/TPS/IAC stuff. Data collected while driving around really isn't what you need for adjusting VE in the idle regions. Doing that will lead you astray... hard starts, surging idle etc.

Reseting the after start parameters to factory settings fixed the issue. I was going to ask what next and maybe why I ended up with this issue. Looks like you beat me to the punch. So to tune the VE table for idle, I'm thinking to start it when it is hot, let the idle settle down to the target RPM. Then reset the fuel trims and start scanning. After that is good, smooth the transition to the rest of the VE table and leave the idle cells alone. Then calibrate the Base airflow if needed for cold starts. By the way, the idle is the smoothest it has ever been. Thanks again for all the help.