I have a drive by cable DBC setup. I built the engine and used the PCM as well as throttle body from a 2001 Chevy Tahoe. I swapped the cam and am trying to calibrate the throttle body & idle air controller (IAC). I have several questions...
IAC steps: do more steps equate to more air (opening farther?) or vice versa?
IAC count what is a good IAC count to shoot for in idle, park, no AC at operating temp?
I have a mild cam. Not sure where I put my cam card. Nothing extreme but bigger than stock.
Yes higher steps means the IAC is open further.
I like for them to be less than 15 at warm idle in park.
Another thing you can do is to slowly open the throttle with the set screw once its up to temp. that will lower the IAC steps. But you have to do a TPS relearn once you adjust the throttle any.
A general rule is 20-40 counts on a cammed vehicle and for stock vehicles I’ve seen 60-80 posted in the past.
If you do crack your throttle blade open to achieve a lower count value at “hot” idle, then be sure to run your base running airflow config again to dial that back in. It shouldn’t be off by much if any simce your using a stock throttle body but make sure your idle desired air is matching your dynamic air
Awesome, thanks @RDF1 & @Firebirdmuscle
Do you filter (moving average or anything) the IAC PID? Mine jumps all over the place. I'm logging "Idle Air Control Desired" and "Idle Air Control Position"
Resetting IAC / TPS relearn: bit confused here. So do I unplug just the IAC or the TPS and IAC? Then cycle "ignition on" w/o starting for 30 seconds and reconnect.
Forgive me if this is somewhere in the forum. I couldn't find it searching here or internet.
the tps relearn is unplugging the tps then ignition on for 20-30 seconds, ignition off, then reconnect.
No sir, i do not filter either of the IAC
Last edited by Firebirdmuscle; 10-22-2022 at 08:34 PM.
Just be sure the TPS % is reporting 0 after your adjustments. Sometimes a battery disconnect or a write entire is needed to clear the min TPS voltage stored.
IAC 0 fully closed.. no air
IAC 160 fully open. As much air as it can let in..
Tuner at PCMofnc.com
Email tuning!!!, Mail order, Dyno tuning, Performance Parts, Electric Fan Kits, 4l80e swap harnesses, 6l80 -> 4l80e conversion harnesses, Installs
To clarify, does the TPS & IAC need unplugged in the relearn procedure? Or just the IAC?
Thanks!
Just the tps needs to be unplugged. Key off unplug tps, key on for 30 seconds then key off and plug tps back in. That's how I lowered my counts.
Just for clarification unplug both TPS and IAC? I've been unplugging both?
It doesn’t matter that your doing both but when resetting tps technically you only need the tps unplugged.
Okay awesome thanks. Another question. After the reset it always seems to fluctuate between 0% and 0.4%. My TPS voltage is under 0.55V. Seems like it would be normal but just double checking?
I want to make sure I can lay throttle calibration to rest knowing I've done it correctly. My bigger tuning challenge is hot start...
Background: I adjusted the Idle Spark Advance tables for In Drive and In Park. (0.08 Airmass, 0 RPM) to (0.24 Airmass, 1200 RPM) set to 29 degrees and blended in on both tables. Seemed to help my startup but not fix my hot start issue.
Issue: once engine is to operating temperature and I let it set for a few minutes; say I go in the store to buy something and return. Then the truck doesn't want to start. I have to crank it for several seconds.
Otherwise, once it's started, if I shut it off and crank it again it fires right back up.
If engine is cold, and I crank it, it starts right up.
Only if engine has been brought to temp, then shut down for a few minutes do I seem to have the startup problem.
Been trying to collect data and calibrate the throttle body as well. Haven't had too much luck.
I've also calibrated MAF and Main VE Table. Not touched high octane or Low Octane advance tables though; wondering if those need to resemble the idle tables as there's nearly 19 degrees of separation after I updated the idle tables.
Any additional theories / thoughts? Thanks!
Last edited by weinerschizel; 10-22-2022 at 11:16 PM.
My first thought would be fuel pump check valve or pump is weak when getting warm.
Leaking injectors dumping some excess fuel while sitting?
Interesting! Great theory! Okay so I have all new injectors (not so say they are good). However, my pump is 255,000 miles on it. That said it worked with previous engine fine but I do need to replace it just due to age.
UPDATE: Ordered OEM replacement fuel pump and sending unit. Looks like this is going to be real fun job *sigh*
Last edited by weinerschizel; 10-23-2022 at 08:28 PM.
Installed new fuel pump. No change in startup. I think it's something in the tune. Still cranks quite a bit once engine is up to temp.
Originally Posted by weinerschizel
That's not going to be related to TPS or IAC.
if you occasionally see 0 and occasionally see 0.4% that means either the blade is sticking or the TPS sensor is. Sometimes the TPS engagement to the throttle shaft is loose and can be taken up by wrapping it in electrical tape. I'd say 0.4% isn't a need for concern. There is a little wiggle room in the min TPS %. You can check to make sure it is going into a idle mode by checking to see if LTIT's and STITS's are active while stopped. They will no update while the vehicle is moving.
Tuner at PCMofnc.com
Email tuning!!!, Mail order, Dyno tuning, Performance Parts, Electric Fan Kits, 4l80e swap harnesses, 6l80 -> 4l80e conversion harnesses, Installs
@Alvin - I think I didn't have it reset correctly.
Got the throttle calibrated. I had another tuner help me. He had an awesome way to do it...
Open throttle cracker w/ engine running till IAC counts get close to zero on VCM scanner. Reset the throttle (may have to do several times in process of opening setscrew). Start engine, set IAC to zero in VCM scanner. Then close throttle setscrew till engine doesn't want to run. Open it slightly, and should be calibrated. Now my truck idles around 15 IAC. He said lower IAC is better for my setup.
Thanks for help!
Still doesn't want to turn over when set at operating temperature. I have a new Crank sensor (already did fuel pump & cam sensor). If that doesn't fix it, I'm going to order tools to do an injector leak down test. That said, I think I want to ditch these Delphi injectors anyways. I'll looking for a good set of OEM or other quality brand I can swap in. I think I'm running the stock 24# if memory serves me right, I'd like to do a bit higher so I have some headroom for upgrades.
What are the cam specs?
When you mean it doesnt want to turn over.. do you mean the engine spins over but doesnt fire up?
578/587/213/220/114+4A
Engine warms up, then is turned off and allowed to cool down for a few minutes. It will crank but takes several seconds to fire up.
Engine starts perfectly if is a cold start or if is turned off then started again right away.
Only if engine is warmed up thenturned off and allowed to cool a bit do I have the issue turning over. It will start every time but have to crank it for several seconds.
hmm, ran into those exact same warm startup symptoms and found it was the fuel pump check valve. I know you said you replaced it, but if there was a tiny bit of debris in the tank that stuck in the check valve of the old one, it could have buggered the new one as well. Definitely could be in the tune (cranking fuel tables that vary by engine temp and time since last run) but would be nice peace of mind to throw a fuel pressure gauge on it just to be 100% sure its holding fuel pressure when shut off, and building instantly on key on.
Reply With Quote