Low Idle Vacuum Tuning
I've been experiencing a hanging idle situation. The car is manual transmission. The RPMs don't drop when clutching. IAC counts have been adjusted to less than 10 at idle (set to 805). Loop Rates & Decel Open IAC values have been adjusted. No change to how quickly the RPMs return to idle.
My cam specs are: Duration 246/256, Lift .570/.590. At 805 idle the vacuum is less than -3. FiTech first told me my MAP readings didn't look correct. Installed a trimmed orange MAP seal from them and still had no change in idle return. They asked that I request an RMA to diagnose the ECU/MAP sensor. I Issued a RMA request and was told it's not the ECU/MAP, it's due to the low vacuum at idle that's the cause of the hanging idle. It was recommended that I set my idle to 1200 rpm to raise the vacuum. Is there something else that can be done to tune for the low idle vacuum? Not a fan of 1200 rpm idle.
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I faced a similar issue and spent countless of hours working on fixing it and changing settings. My idle will hang above 1,000 rpms and then after 10 or so seconds go down to the setting. After all that, I figured that the problem was with the adjustment of the secondary butterfly. Look down at the butterflies, specifically the secondaries. They may be staying slightly open at idle. You can try closing the secondary butterfly manually to see if it makes a difference.
Look at: https://fitechefituning.com/fitech-efi-tuning-forum-2/topic/1971-mustang/?part=3#postid-3534
and follow this method:
Quote from Mach1Cleve on August 18, 2020, 4:41 pmI've been experiencing a hanging idle situation. The car is manual transmission. The RPMs don't drop when clutching. IAC counts have been adjusted to less than 10 at idle (set to 805). Loop Rates & Decel Open IAC values have been adjusted. No change to how quickly the RPMs return to idle.
My cam specs are: Duration 246/256, Lift .570/.590. At 805 idle the vacuum is less than -3. FiTech first told me my MAP readings didn't look correct. Installed a trimmed orange MAP seal from them and still had no change in idle return. They asked that I request an RMA to diagnose the ECU/MAP sensor. I Issued a RMA request and was told it's not the ECU/MAP, it's due to the low vacuum at idle that's the cause of the hanging idle. It was recommended that I set my idle to 1200 rpm to raise the vacuum. Is there something else that can be done to tune for the low idle vacuum? Not a fan of 1200 rpm idle.
Just for another data point, I have a cam with specs Duration 268/284 @ .05, and Lift 0.766/0.792, with LSA of 108 deg, and idle at 1000 rpm and I get 5" Hg vacuum. I wonder if you could have a vacuum leak. There is an idle adjustment in the controller "loop rate down". By increasing that, you can get the idle down to your target quicker after startup.
Tony-Muscle:
I'll try that method outlined to you to set the IAC. FiTech told me to only adjust the primary screw. If both screws are turned in the same amount does that equate to both sets of butterflies being open the same? Your secondaries are closed more than your primaries? Regardless of butterfly position, both sets actuate in unison? Seems to be a lot of backlash/slop in the linkage setup.
Bdhulderman:
I've smoked for vacuum leak when I had a carb and after installing the FiTech. Nothing was found. Perhaps after I try Tony-Muscle's method the Loop Rate Down will work.
I've tried the above mentioned suggestions. The idle return response is great when started cold. However, when the engine does warm up the hanging idle presents itself. Also tried idling at 1200 rpm per FiTech's recommendation to increase idle vacuum. The idle still hangs.
Are there any other thoughts?
I'd like to know what your vacuum reads in the log file when cold. Could be something that rears it's ugly head when it warms up related to engine vacuum, because your vacuum at -2.5 in the log file is way low for your camshaft. For a second opinion I would use your own vacuum gauge to see if they read the same.
I placed a mechanical vacuum gauge on the cold start this evening. Read approximately -3 which corresponds to the FiTech handheld value.
I've attached a PDF of the cam card. Any thoughts on it would be appreciated.
My experience with FiTech has been great. Indications are it's just not a great relationship for my engine.
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Very strange that I can't find the Lobe Separation Angle (LSA) of your camshaft. Now I have to compute it myself based on the open and closing info.
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When I compute the overlap in my camshaft, I get at advertised duration about 108.3 deg, with your camshaft it's about 71 deg, significantly less, indicating you should be getting higher vacuum at idle. Something is wrong with your build, maybe try a leakdown test while hot.
Is the fitech controlling your timing? What is your base timing at idle and are you using vacuum advance? Timing really affects vacuum level. I'm at about 6" in gear (700r4 auto) but no hanging rpm issues. I idle at 900. Maybe I missed it but did this hang before the fitech? Is it possible to upload the .csv file of your log so I can see all the data on one line to see iac and idle and timing etc?