2001 4.3 Vortec Why are IAC counts increasing after shutoff of eng

[gnnova]

I have a 2001 S10 Blazer with the 4.3 Vortec and a 0411 computer. I have the MAF disabled to run in speed density mode. After the engine is warmed up. If you shut it off and let it set for a feww minuted. When you turn the key back on before you started it the IAC counts will be at 84 which is up from 50 that it normal runs at when warm. When it is then started, the LTFT will be at +18. It will struggle to idle for a few minutes until the IAC counts come back to 50 and the LTFT will be near 0. If you shut it off and start it right up is does not do this. It is only after it is warm and it sets for a few minutes. Also does anyone know if the missfire monitoring is disabled when the MAF is disabled to run in speed density mode.

Ken

[Alvin]

Look for IAC park position or idle park position. It returns to that with key on/ engine off. But IAC has nothing to do with fuel trims. A log might be helpful to figure out your issue but it sounds like its just lean during restart.

Misfire still works in SD Mode.

[gnnova]

Thanks Alvin I looked at the IAC park setting and it was at 174 for the temp I was at. So I set the park settings in accordance with my Idle dersired air settings. This did nothing to help. I looked at the eng coolant temp and Intake air temps and they were showing normal at 196 deg for ECT and 105 deg for IAT. What else could be causing this issue. It seems that something is telling the eng it is cold and adding fuel and air at idle. If it is a vacuum leak why does it go away after a couple minutes. Also the missfire recording is disable in SD with my computer because I tried pulling a spark plug wire and no missfires were recorded when it was running. If anyone knows if there is something I can do to remedy this let me know short of taking it out of SD mode.

[charcoal03silvy]

The IAC isn't the issue here, it's behaving as it should. It will need additional air to startup. It sounds like you need more hot afterstart enrichment and delay.

[blindsquirrel]

P0300
Conditions for Running the DTC

Important: If the start-up engine coolant temperature (ECT) is less than 7*C (20*F), misfire detection is delayed until ECT is more than 21*C (70*F). If the start-up ECT is more than 7*C (20*F), misfire detection begins after a 5 second delay.

- DTCs P0101, P0102, P0103, P0117, P0118, P0128, P0335, P0336, P0341, P0343, P0500, P0502, P0503, P1114, P1115, P1121, P1122, P1220, P1258, P1336, or P1345 are not set.
- The fuel level is more than 10 percent.
- Then engine speed is between 450-5,000 RPM.
- The system voltage is between 1-16 volts.
- The throttle position (TP) is steady within 2 percent for 100 ms.

[gnnova]

So Blindsquirrel So if I understand correctly the computer needs to be counting missfires to set DTC P0300. So to prevent a DTC P0300 from being set when codes P0101, P0102 & P0103 are set to go into SD mode it will disable the missfire counting. That is a bummer because I am chasing a missfire issue and was trying to eliminate the MAF. It seems to run better in SD Mode. Thanks

[gnnova]

The IAC isn't the issue here, it's behaving as it should. It will need additional air to startup. It sounds like you need more hot afterstart enrichment and delay.

Thanks I will take a look at this tomorrow.

[blindsquirrel]

It will not set the P0300 - it might or might not increment the misfire counters. I have seen them do it both ways with MAF failed and codes set.

[gnnova]

The IAC isn't the issue here, it's behaving as it should. It will need additional air to startup. It sounds like you need more hot afterstart enrichment and delay.

I found an Afterstart enrichment under Fuel/Cold Warmup but no Hot Afterstart anywhere. So it had a Decay Delay and a Initial Adder vs ECT under its heading. I worked my way from 38 sec to 58 sec on the Decay Delay and from .130 to .220 Multiplier in Initial Adder vs ECT in the effected temp ranges. It didn't seem to help much. There is another Decay Delay and Initial Adder vs ECT under PN/Drive Enrichment. Could this be where I should be making the adjustments?

[gnnova]

It will not set the P0300 - it might or might not increment the misfire counters. I have seen them do it both ways with MAF failed and codes set.

Thanks. I will work with it. It does run better in SD Mode and with no missfires counting the Torque converter doesn't keep unlocking. The missfires I'm having is not bad enough to set the P0300 DTC but enough to cause the TC to unlock now and then.

[gnnova]

Here is my tune if anyone wants to look at it. The motor is stock with exception of the camshaft that is from a mid 90's CPI 4.3. The cam has 208deg duration at 50 and somewhere around 116deg of overlap. The injectors are 36lb from Aus injection with their setup specs in preparation of doing a tail pipe turbo when I solve the missfire issue

2001 Blazer New O2s deleted MAF Raised after start enrichment & Delay longer 2-26-23b.hpt

[gnnova]

Looks like the parameters under PN/Drive are the ones that are used to correct my issue. Reset my settings to the previous values in After Start and applied them to the PN/Drive sections with the same name and my after start issue has been corrected. Doesn't make sense why they named them that way but it works. Thanks charcoal03silvy for the help. Also thanks everyone else for your help.

[blindsquirrel]

The missfires I'm having is not bad enough to set the P0300 DTC but enough to cause the TC to unlock now and then.

No, re-read the text I quoted from the service manual. If you are in SD you must have either P0103 set as current if MAF is just failed, or P0102 & P0103 if MAF is removed altogether. If those codes are present, which they must be if it's really in SD, then the tests behind the P0300 do not ever run, and if they do not run it cannot set a P0300. It's not allowed when MAF codes are present, it doesn't even bother to check.

[gnnova]

No, re-read the text I quoted from the service manual. If you are in SD you must have either P0103 set as current if MAF is just failed, or P0102 & P0103 if MAF is removed altogether. If those codes are present, which they must be if it's really in SD, then the tests behind the P0300 do not ever run, and if they do not run it cannot set a P0300. It's not allowed when MAF codes are present, it doesn't even bother to check.

When I was talking about the P0300 code not being set but missfires were effecting TC lockup. I was running with the MAF enabled and not in SD mode. Sorry if my statements were miss leading.