Hot Restart Idle Issues
 

Sorry for the novice question, but can someone check out my idle logs. The car idles pretty good when cold started and into hot, even after driving and everything, just as long as it started cold it will idle fine. When I turn it off and wait 10 mins or something it won't idle anymore. I don't really get whats going on. I'm new to ms3 and I'm not the best idle tuning. I just got the car started not long ago and haven't been driving it much because I can't figure out this idle issue. If anyone can maybe check the logs and tune file to see the issues, there probably are a lot. (cold Idle log is too big to upload since its from cold to hot)

This is a common problem. Especially with larger aftermarket injectors. There are plenty of threads about this topic. I would recommend reading those first. I have been working on this and plan to make a post about my improvements in the next few days. It is a lean issue after hot start.

Ah ok cool. Sorry about that, most of the topics I saw got sidetracked with different idle issues so I must not have seen the lean issue while looking through them. Im gonna try some stuff to help it.

Look for threads that refer to the ASE Tapper...

thanks a lot, messing with ase is helping it. will keep messing with it to get it as good as I can.

Do you have an NA or NB? This is an inherent issue for NB (returnless) systems, as stated above tweaking ASE is key.
Others have attributed this to IAT heatsoak, so try to isolate the issue either to your IAT or injectors (or both) first.

It is not a Returnless problem. I have direct experience with converting from RL to Return style on my '99. Did not change this. Either way, one tunes idle VE and dead time. The injectors get hot from the sitting engine. This changes the resistance of their copper windings, and the dead time (the real dead time) increases (ohms law... V stays the same, R goes up, I goes down). It is I that drives the injector to open. Thus the fueling goes down. To compensate, you have to increase the PW. Same effect whether RL or R style. My guess is that if heat soak is worse in NB it would have more to do with the amount of engine heat that is trapped around the injectors between the various intake designs. Then, once the fuel and air flows for a bit, cooling the IM and the injectors down, the dead time shortens and more fuel is delivered, so the PW can be brought back to normal.

IAT heat soak is easy to deduce. Is the reported MAT higher than real or not? Log shows MAT = 53*F. Air Corr is 100.4. Those two things together do not indicate a heat soaked IAT. If it were heat soaked, it would show 100* or something, and then the correction would be around 98% per MAT correction curve. Still not drastic. I don't think it is the driver in this case.

Go to the linked thread above and see just how much ASE, Taper, and EGO are needed to make hot restart issues disappear.

EDIT: You may wish to change the EGO authority in idle area (or near idle) from 5 back to 15.

DNM

Thanks, yea I have an NA. I recently swapped my head for a vvt head, this only started after the swap. Gonna continue to work on the hot starts, today i got it so it doesn't die anymore on the restarts but its still lean, like 15.6 or so a little after the start. I still have to work on it but thanks for all the help.

When it's at the 15ish hot, does it idle smoothly still?


Even the OEM system will lean out on a hot start.
My NB with the OEM ECU + narrowband (plus a separate wideband not wired to the ECU) will generally idle around the 15ish AFR area for maybe 5mins after a hot start.

What does your OEM system idle at normally?

Normal idle, once warmed up etc fluctuates between about 14.5 and 15 (typical closed loop narrowband pulsing)

Ice cold start it will idle at around the 12s for maybe 1 min before tapering back up to the usual 14s

Hot start it will often idle around the low/mid 15s for 5mins or so (or until you start driving and come back to idle)


Setup is a stock 99 Aussie spec MX5
OEM ECU
EGR deleted, coldside short intake
Extractors with OEM narrowband in stock position on #3 runner.
Separate wideband installed just past bellhousing (MTXL) (not hooked up to ECU)

I have seen various discussions on heat soak potentially affecting injector dead time - one thing I am curious about is how the stock ECU and Fuel System handle hot restarts. Does the stock ECU have a similar mechanism to ASE taper, where it can command higher injector PW on "hot" restarts? One other piece of the puzzle is the PRC valve, which references the FPR to atmosphere for a short duration on hot restarts, which would effectively do the same thing. Has anyone here tried to tie the PRC valve into a standalone ECU to maintain functionality? I've thought about testing the concept, just unplugging the manifold reference line on a hot restart to see if it richens up enough to actually make a difference.