IAC Counts and Split BLMs
IAC Counts and Split BLMs I have a couple of things going on so Ill start with the IAC Issue. I have a BBK 58mm TB, I do have the IAC ports Isolated OEM Style so its not bleeding out right behind the TB Plates. The only thing I have not done was drill the IAC Hole at the front of the TB. My IAC count shows 62 Counts after about 10 min at idle, They started around 70 at first start up and where at around 64 when the system went into Closed Loop. At the end of my idle log LTFT Bank 1 was at -12% and LTFT Bank 2 was -1%. My question is, would an IAC count that far off from cause such a large difference? At cruise my LTFT are reading near zero, but on decel (Full Lift on TP) I've started experiencing small amounts of back fire out the exhaust that wasn't present last year.
Performed all the typical Diag, TPS and Map look good, No Vacuum leaks (Triple Checked) No leaks in or around MAF and TB. Not using the stock rubber intake between the MAF and TB went to a hardware store years ago and picked up a black rubber reducer with the correct size for the MAF and TB ends, It fits perfect.
Ill drill the IAC Passage on the front Side of the TB and watch my count and step up in bit size until I get my IAC's within an acceptable range. Then ill perform a GM LTFT Reset and watch my numbers from there. Hope that'll be the end of it. But from the research I've done I have a 50/50 chance of it solving the issue.
Staging Lane
Joined: Sep 2018
Posts: 54
Likes: 3
From: In the mitten
Has it been tuned? Min. Air Rate too low would.get IAC counts high. Have you tried to adjust throttle plates to get IAC counts in line? Leaking FPR or dripping injector(s), higher than specified fuel pressure will cause - fuel trims. Do O2 cycle from .050 to .999 ?
If there is a condition causing PCM to add counts to correct idle it may also be reflected in fuel trims. Misadjusted throttle plate with a correct TPS value shouldn't.
If there is a condition causing PCM to add counts to correct idle it may also be reflected in fuel trims. Misadjusted throttle plate with a correct TPS value shouldn't.
Has it been tuned? Min. Air Rate too low would.get IAC counts high. Have you tried to adjust throttle plates to get IAC counts in line? Leaking FPR or dripping injector(s), higher than specified fuel pressure will cause - fuel trims. Do O2 cycle from .050 to .999 ?
If there is a condition causing PCM to add counts to correct idle it may also be reflected in fuel trims. Misadjusted throttle plate with a correct TPS value shouldn't.
If there is a condition causing PCM to add counts to correct idle it may also be reflected in fuel trims. Misadjusted throttle plate with a correct TPS value shouldn't.
Yeah, It was tuned when I did the cam install about 5 years ago, then tuned again when I moved and elevation changed by 4k+ feet. I was in CO Before now in IN. O2's were cycling fine on my last log, but Im still going to swap them and see if my FT swap banks. I did have a leaking FPR about 4 weeks ago and I replaced it with a stock AC Delco Unit. The injectors are factory, the car only has 55k miles on it. But still, they're over 20 years old so that could be a possibility. I was thinking about sending them out to be flow tested and cleaned at the end of the year anyways. Before I go through the pain in the *** of jacking up the car to swap O2's Ill see if adjusting the Throttle Plates helps.
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TECH Veteran
Joined: Apr 2008
Posts: 4,985
Likes: 112
Not sure how you modified the 58 TB so it has a functioning IAC port. If you do drill start 1/8" (stock size IAC hole) and scan IAC counts again. If still high increase hole in 1/64 increments as just that small amount makes a big difference. They want to be 32 (30-35) at idle at full operating temp. Currently at 60 ish they may peg at, IIRC 120, when AC is on and you are doing a turn (power steering pump) and the car can die because idle is to low then
IMHO you would be better served using your stock 48 mm or having it bored to 52
for injector service I have used cruzinperformance.com a few times. Rich is a good guy and knows his stuff
The other "fix" for 58 TB would be to crack the TB blades slightly to get IAC counts right but then you will need to slot the holes on the TPS to get those counts (VDC) right. With the holes slotted you rotate the IAC back so it tricks the TB into seeing the right VDC. There is a write up, IIRC, on the Golen Engine site and likely on this forum also
IMHO you would be better served using your stock 48 mm or having it bored to 52
for injector service I have used cruzinperformance.com a few times. Rich is a good guy and knows his stuff
The other "fix" for 58 TB would be to crack the TB blades slightly to get IAC counts right but then you will need to slot the holes on the TPS to get those counts (VDC) right. With the holes slotted you rotate the IAC back so it tricks the TB into seeing the right VDC. There is a write up, IIRC, on the Golen Engine site and likely on this forum also
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Not sure how you modified the 58 TB so it has a functioning IAC port. If you do drill start 1/8" (stock size IAC hole) and scan IAC counts again. If still high increase hole in 1/64 increments as just that small amount makes a big difference. They want to be 32 (30-35) at idle at full operating temp. Currently at 60 ish they may peg at, IIRC 120, when AC is on and you are doing a turn (power steering pump) and the car can die because idle is to low then
IMHO you would be better served using your stock 48 mm or having it bored to 52
for injector service I have used cruzinperformance.com a few times. Rich is a good guy and knows his stuff
The other "fix" for 58 TB would be to crack the TB blades slightly to get IAC counts right but then you will need to slot the holes on the TPS to get those counts (VDC) right. With the holes slotted you rotate the IAC back so it tricks the TB into seeing the right VDC. There is a write up, IIRC, on the Golen Engine site and likely on this forum also
IMHO you would be better served using your stock 48 mm or having it bored to 52
for injector service I have used cruzinperformance.com a few times. Rich is a good guy and knows his stuff
The other "fix" for 58 TB would be to crack the TB blades slightly to get IAC counts right but then you will need to slot the holes on the TPS to get those counts (VDC) right. With the holes slotted you rotate the IAC back so it tricks the TB into seeing the right VDC. There is a write up, IIRC, on the Golen Engine site and likely on this forum also
LE2 Heads, CC503 Cam, 1.6RR, ARP 7/16 RS, Thicker PR, BBK 58mm TB, Ported IM, LT Headers, Off-Road Y-Pipe to Pre Axle Dump, A/C Delete, E-WP, MSD Coil, MSD Cap/Rotor, Aftermarket Clutch (Dont remember brand installed in 07) Stock T-56, Dennys DS, Moser 12 Bolt, 4:10's, Moser Larger 33 Spline Axles, C-clip Eliminator kit and Detroit Trutrack. Also have a Bunch of BMR Suspension Components But not really relevant
Well ****, I drilled OEM size IAC hole in the front of the TB. Started the car and started logging my idle. Neighbor was outside so I started talking to him, while we were standing there talking after about 15min and about when I was going to shut the car off and look at my log the car just shut off. So I walked back over to the car saved my log for later review and got a crank no start. Instead of just cranking the car I turned the key to the off and when I attempted to start it again just got a "Clunk" First thought was starter, battery or battery/cables/grounds. But that still dont explain why it died, Unless the Alternator is bad so I conducted a quick V test on the battery and it was 11V but I don't have a load tester so the battery is still on the fence. I threw my charger on and I went into the house to review the log, I watched all parameters, and they were good and remained constant all the way till it died. On the plus side my IAC Count dropped to 52 at its lowest so that's a step in the right direction with that issue. I went back outside and attempted to turn it over one last time, cranked a couple of times no start then clunk on the 3rd attempt. I got out of my car and smelled fuel. I thought "WTF?" I went to the fuel rail, lines and FPR and looked/felt all around and no fuel. I looked under the car and there was a giant puddle of fuel under the car. I still could not find where it was coming from and since the car is lowered that makes it more difficult. My driveway has a slight slope to it, so now I get to attempt to push it into my garage so I can get it in the air for a proper Diag of all this crap.....shiiiiiiiiiiiit 2020 sucks *** but at least im headed in the right direction with my IAC issue lol
Teching In
Joined: Jan 2015
Posts: 2
Likes: 0
From: NL
Very interested to see what happens here. I've been fighting with split BLM's and IAC count issues for a couple of summers now. Been through all the normal causes... spark, injectors, O2 sensors, vac leaks, exhaust leaks, wiring, etc. multiple times, but to no avail. I've been cracking my throttle blades to set my IAC counts. I have no trouble getting them where they should be after the car is warm. However, on a cold start, they won't go lower than say 70-80, which my tuner is telling me is not low enough. Only today did I stumble upon this issue with the aftermarket throttle bodies. I'm actually running a TPIS 58mm throttle body, which also has the IAC ports to the larger plenums. The only thing is, I also have a TPIS miniram, which doesn't have the idle air passage to the runners. Does this mean I'm stuck with the split BLM's, or is it still possible that drilling the throttle body hole larger could even things out?
My setup for anyone wondering:
396 LT1 Stroker
AFR 195 Comp Heads
CC Custom Grind 238/244 .582/.579 112+4
1.6 RR
TPIS Miniram
TPIS 58mm TB
85mm LS MAF
EFI Connection 24x Upgrade
0411 PCM
Kooks 1-7/8" Headers and 3" true dual exhaust
4L80E FLT Trans
All accessory stuff except power steering deleted
My setup for anyone wondering:
396 LT1 Stroker
AFR 195 Comp Heads
CC Custom Grind 238/244 .582/.579 112+4
1.6 RR
TPIS Miniram
TPIS 58mm TB
85mm LS MAF
EFI Connection 24x Upgrade
0411 PCM
Kooks 1-7/8" Headers and 3" true dual exhaust
4L80E FLT Trans
All accessory stuff except power steering deleted