76 280z microsquirt project

[Datsunpowers]

Darom, wanted to say a big thank you. My PTZ throttle body was making the same whistling noise, and it was driving me crazy. Grinding the sharp edges off tonight reduced the noise to an acceptable level. It's much improved now!

 

I hope I can help you out with your closed loop idle settings. I spent a lot of time working to get my car to idle properly at 750 RPMs with the PTZ throttle body. I had to recenter the throttle plate and close the throttle screw closed more with a little grinding on the stop. I also had to change out the GM IAC motor with a different model. The one that came with the throttle body would not close and seal for me all the way. So, I went to the junk yard and pulled several different GM IAC models. The IAC that is working for me I think it came from a Grandprix V6. Here are my Megasquirt closed loop settings. I hope this helps you out.

Thanks, Tom

[darom]

Hi @Datsunpowers Tom!

I appreciate your time posting your IAC setup here.

 

I wish Protunerz would grind the sharp edges at their factory. I talked to them, they are aware of all this whistling business with their intakes. They are great guys and I got quick tech question responses from them. But the noise is an embarrassment to a pricey car part.

 

I have a few questions for you:

- Do you set up your throttle blade to be completely closed and then configure your IAC to provide additional air to get your target 750 rpm?

I went over this subject on a msextra forum as well, and it appears there are 2 ways to do it. One is to open the blade a little and IAC completely closed at idle. Another - the throttle blade is physically closed and IAC is providing air for idling target speed.

 

I went with the 1st option, since I couldn't get my IAC to provide predictable behavior. One day it would be idling at 900 rpms, next day - 800-850 rpm, another - around 1000 rpm. I figured the IAC's min steps and step size needed to be played with and per Madcaw's advice, I left it on 'Always On'. This helped somewhat. I also bought another IAC for a 1999 Camaro V8 (Ultra-Power AC162) to test (10$ special from Rockauto), but I haven't installed it yet. I suspect my IAC is not completely sealing the opening, thus these fluctuations.

 

- Open-loop vs closed-loop question

I removed my a/c a while back, and I have a 5-speed. I thought the closed-loop idle control is suited for the cars with big electrical loads (like electric fans, a/c compressor kicking in) or an automatic transmission. I have a belt driven fan. All my headlights are converted to using relays. I set up the open-loop since it was the easiest option.

Would you recommend for my car to switch to the closed-loop idle control?

 

If you don't mind checking my tune/idle and a driving log, I'd appreciate it.

 

What are your car's specs? Can you share your tune?

 

Thanks!

Den

2025-05-18_13.51.43.mlg 2025-05-18-adj-IAC.msq 2025-05-10_11.12.19-driving.mlg

[Datsunpowers]

Darom, I agree with you that the ProtunerZ guys are very helpful, and stand behand their products. I am so glad that the car doesn't whistle anymore. 

 

I am no expert here, so take this as advice. Your mileage my vary. 🙂

 

The car is a 71 240z. I live at 8,000 feet and I see a lot of altitude change to 5,600 feet in CO, so I am running %Baro.

 

Here is the setup on my engine:

3L Turbo Stroker, 88mm JE forged pistons 8.43:1, Max Speed rods, ARP head, rod, main bolts, Electramotive L7 Cam, Garret GTX Gen II 3071 turbo, Water-to-Air Intercooler, ProtunerZ intake, turbo manifold, downpipe, Arizona Z Car 7 QT oil pan. Megasquirt V 3.57 with the expansion daughter board, sequential injection, 280zx Turbo CAS, GM Truck COP, Bosch 440CC injectors with 43 Psi. This is a new engine that has about 2,000 miles on it. Its running very well over the stock turbo engine I had in the car.

 

I did set up the throttle blade to be completely closed and then configured the IAC to provide additional air to get to the target of 750 rpm. This has allowed me to have it start in the cold at -10F and 90F and warm up properly. I do find it likes a AFR of 13.5 for a good smooth idle at 17 degrees of timing at 750RPM. I enclosed my MSQ tune file

 

Looking over your setup I noticed a couple things you should check. I will make the assumption the engine is stock with no cam and stock cam timing.

1. The throttle position sensor: You have 464 steps where mine has 679 steps. I would make sure it has full travel and re-calibrate it. I also noticed that your sensors are unlocked. This could be the sensitive throttle you mentioned.

2. MAP sensor: Looking at the one warm up idle log. The timing moves from 19 to 23 degrees with no TPS input. Then is settles down to 14.8 while the MAP remained fairly steady at 41 kPa. You would think this would change with the timing swings, so check your MAP hose to the MAP sensor and the MAP sensor wiring. I see you have a GM-1Bar sensor configured. On my engine I have a vacuum of 27 kPa. It could be normal for your engine but check for vacuum leaks also. Here is a great article from DIY Auto Tune on closed loop ldle. MS3Pro Closed Loop Idle - Stepper Valve - DIYAutoTune.com

3. I would adjust your timing at the lower values. Set it up so you have 500 = 19 and have 17 degrees at 750. this way it will give you a little timing when the electrical load increases to bring the RPM back up. Looking over the idle/accel tab I have more settings available and a 16x16 table to play with. I think this is the limitation on the Microsquirt vs the Megasquirt.

4. it can't hurt to double check your base timing. I would confirm it at (Fixed Timing setting set to 15 degrees) with a timing light. Make sure you confirm zero TDC with the piston at TDC. I have had a couple harmonic balancers spin on me. I am not sure how the missing tooth crank wheel bolts to the balancer.

 

I included my current tune and a data log. In the middle and end of the log you can see how it idles. 

Hope this helps.

CurrentTune.msq 2025-05-21_16.32.19.mlg