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So I had my car tuned and the tune is *dialed*. Cold start, AC on or off, doesn't matter, idle is beautiful. Cam only LS1, not a huge cam, 42# injectors. I can drive around all day long and never run in to a single issue. Pulls fantastic at WOT. The issue I have is once I go WOT, the idle starts to hang at over 24MPH (my idle down speed in HPT). Under 24MPH, with the AC on, in Drive, idle will slowly dip to 500rpm and stall. Bump the key and fires back up. It then behaves till the next WOT pull. If I leave the AC off, it will do fine besides the intermittent hanging idle. It almost seems like the IAC is lazy, but car only has 30k miles.
Is the intermittent hanging idle and the stalling two different issues? Have you looked at the "Throttle Cracker Airflow vs. RPM vs. Speed" in HP Tuners? My truck seemed like it was on cruise control rolling down the hwy with the throttle closed. Lowered the MPH on the cracker and the RPM's dropped normally.
Is the intermittent hanging idle and the stalling two different issues? Have you looked at the "Throttle Cracker Airflow vs. RPM vs. Speed" in HP Tuners? My truck seemed like it was on cruise control rolling down the hwy with the throttle closed. Lowered the MPH on the cracker and the RPM's dropped normally.
I mean, it's two different issues, but they don't show up until I go WOT. If I'm cruising around, I don't get the cruise-controlling or stalling. Did I answer that correctly? I'm hesitant to change the time cause before I go WOT, it runs really really good! The idle characteristics are spot on, including the throttle cracker/follower.
So I did some more data logs. It's super weird. My IAC is not behaving correctly. I caught one stall and another near-stall. For whatever reason, after going WOT, my IAC just drops to zero when approaching idle. It's driving me crazy. Anyone have any ideas why this is?! It's ONLY after a WOT (or near WOT) pull... It happens in the attached log at about 19:20:53.
I am by no means an expert, and you probably are more knowledgeable than I am. But I did run across this awhile back and may be worth reading . It is a ford post but still some things should apply.
The fight is still on... I swapped alternators (had a bigger truck alt ready to go), did a hotwire kit for the Racetronix I put in. I have PatG rewriting my tune in the 12212156 OS, but that's a total shot in the dark.
I made one modification to my tune recently. I made the the IAC Effective Area no lower than 35 steps. So when the ECU requested lower airflow, there was no way to go below 35 IAC steps. This "worked" and the car didn't die but the car just behaves so odd after getting on it. Idle is way too high when going down the road and when coming to a stop the Idle Desired will sit there and fall and fall until the ECU is requesting 0!!
I'm so frustrated. Even more info, I found a data log where I went WOT and the car did not have the issue and one where it did. The worst part was I made no mods between the two logs. I'm 100% sure of this, there are only 4 days between the logs.
My next test is to see if it's load based or RPM based. Just going to manually downshift the car so it hangs out at a high RPM for a sec. At this point, the only sensors that are the factory 30k mile sensors are the cam position, knock, ECT, CPS, and IAT.
I have a legit, no-BS $50 beer bounty for whoever has the winning answer. Venmo, Paypal, hand delivery, your call.
Have you tried another iac? I had an oem one go bad recently. Also posting your tune would help
Ah sorry, thought it was in the original post. I will upload it tomorrow when I'm back at my computer that has it. Still factory IAC, but data logs show very good, believable data. In addition, the IAT is almost the same when the car is idling fine before WOT and when it idles like garbage after WOT.
As a reminder, I flashed my tune on a known good 0411 ECU and the issue was still there. As a last ditch before replacing the harness, I got yet another ECU and rebuilt the tune on a newer 12212156 OS and the issue vanished. Overall idle quality is way better too. I wish I could say I knew why the car ran great and then suddenly had the issue with no changes, as verified by logs I was taking, but I have no idea. Car runs great, super stoked with it. Highly recommend 12212156 to anyone for the better idle alone.
06-06-2020, 10:07 AM
Odd idle after WOT 
