Cold Start Idle Issue
 

Topic.

Car: 94 FD, GT35r single turbo build, PFC, good compression

So far I'm guessing I'll need to check the TPS or the idle setting in my PFC, it idles a little lean also (about 13.4 AFR at a cold idle) but anyways...here are the symptoms.

On a cold start the car sort of struggles to start up, not much but it doesn't "start RIGHT up". It will do the normal cold start thermowax routine and idle high until the wax melts and the cam moves; however, if I don't keep my foot on the throttle at least a little bit the car will drop below 700 RPMs and stall out completely. The car will idle fine if I hold my foot on the accelerator for a minute before letting off. I've done topic searches and I know it's one of three things but I was hoping for a little personalized assistance if that's not too much to ask.

without any datalogs I would suggest you first check that the thermowax is actually doing something. See this post: https://www.rx7club.com/3rd-generati...6/#post9442162

Has the car always done this or is this new behavior? Do you have an idle air control valve?

Might need the water temp correction or cranking injector time tweaked.

New behavior (last two weeks), the car was tuned and it was fine until then. ACV is next to the TPS between UIM and the firewall, right?

I was thinking this, could you possibly walk me through how to do this with a Commander unit?

The Thermowax unit is definitely doing something, the idle returns to normal and it has no problems whatsoever driving or returning to idle once warmed up- at least I would assume that's because the wax pellet melted and the cam returned to its normal operating temperature position. Edit: That doesn't mean it doesn't need adjusting though, I'll go through the steps in the link you sent me and post the results tomorrow. It's 9pm here and I live in a condo complex and I'm pretty sure my neighbors don't want me running my car in my tiny little garage trying to mess with the fast idle cam

Alright, so I uploaded a video of me going through the steps and checking the VTA readings

VTA readings when the engine was cold

Cam in starting position
VTA 1: .6
VTA 2: 1.48

Cam in full adjusted position
VTA 1: .39
VTA 2 .99

VTA readings when the engine was hot are detailed in the video, but off memory it was .41 and 1.08 in its unadjusted state, so there is a small discrepancy but I'm not sure if that's enough to cause my issue...regardless I'll try to adjust the screw but it's extremely difficult to get to and doesn't seem to want to move by turning it with my fingers. I'd really like to avoid having to take off the intake elbow/TB...but if I must.


Edit: Okay so I read the thread that you linked and one of the symptoms I also have is the car idles at 1.2 to 1.1k RPMs at a stop light when warm and returns to 800-1k RPMs, so if that gives you any more information on what could be going on...also I looked at the video in HD and I briefly saw something leaking out of my downpipe...going to go investigate that.

This is getting really hard to diagnose because I don't have a datalogit log of the problem actually occurring. In the video you showed the TPS voltages but didn't capture the problem occurring. Do you not have a datalogit? If I could see spark timing, ISC duty cycle, TPS voltage, rpm, AFR and injection pulsewidth from cranking until warm idle it would help a lot.

I'm concerned that you were idling In the 14's AFR though. There's not enough margin there and you could get surging or stalling. About 13.5 is leanest I would recommend. You may have a fuel map or warmup correction problem here.

I'm inclined to agree with you, the idle is a bit too lean for my taste. I forgot to take footage of the stalling when I first started it and pulled out of the garage, oops. I'll try to get that tomorrow. I do not have a datalogit, I can ask around and see if there's one I can borrow but this is the best I can do right now. I think I can get ISC duty cycle from the Commander at the very least, and AFR from cold to warm in the same video. I'll do that tomorrow since the car is still probably warm.

Check my edit below the video, I added in another symptom. Car will surge idle when I put it in neutral in preparation for stopping, and then return to 900~ish after a few moments. Vac leak? I also noticed something seeping out of the downpipe/turbo hot side area, but I can't be sure because I only noticed it while I was watching the video I took- I'll try to get more footage of that, too.

Need a datalogit to go any further dude. Just not enough info can be gleaned with videos.

I'll try to find one to borrow, in the meantime I'm gonna try the idle AFR propane test and see what results that produces...I think it might be a fuel map problem, idle and even driving seems a little too lean.

Mods please close this thread, I fixed the issue :) I just played with the injector settings on my PFC Commander, increased the settings up to 107% across the board and it seems to have fixed my lean condition and made cold start up go without stalling

Not really the right way to tune bro.

I'm not really complaining about the results, the car drives a lot more smoothly. I idle at 12.9 and it drops to 10 under boost and the transition is smooth, the cold start problem is gone and it holds 12 afr while warming up. During light cruising I no longer randomly spike to 16 afr...14.5 at max under light throttle. The transition between the primaries and the secondaries coming on no longers produces a jerking feel...I'm sure I could adjust injector duty by rpm but it was lean across the board anyways...

Sounds to me like it was tuned incorrectly in the first place.

I think you are setting yourself up for future headaches with that method of tuning. Now your injector settings are incorrect. If the map needed more fueling why not add it to the inj map? If you dont have a datalogit you can still drive around in map trace mode and take note of your lean cells and add fuel where needed.