4 Dec 2017

Have this week off (well… until Thursday, when I have to clean up the house, then pick up the wife on Friday). That leaves three clear days, to be used wisely.

Today was used to do test drives to deal with the remaining drivability issues: a stumble with getting on the gas, even from idle; a weird surging when coasting in-gear, and an irregular idle:

The stumble was cured by increasing wall-wetting, which cleared it right up. It might actually be a bit too much, because if I rev it off neutral a few times, I can smell gas. Easy enough to fix and drivability has been restored.

The surging when coasting in-gear was due to fuel-cutoff being disabled, leaving the ECU to fiddle with AFR even while coasting. Enabled fuel-cutoff with a combination of MAP and throttle position – solved.

The irregular idle… ah yes. This took the most time to mess with the last time, and even then I wasn’t entirely happy with it – “happy” would be a rock-solid idle that’s no different than an OEM car; frankly I’m not even sure if it’s possible. I worked on that an hour or so and it’s definitely better, steady-state at least. The PID loop needs more work because if idle is disturbed, the control loop isn’t quite there yet, but it’s now much more drivable. We’ll call it a work-in-progress.

One thing that’s going to have to be addressed is the throttle body. Though the throttle plate shaft is tight with no apparent free play, it’s inconsistent as far as where “0%” is. Open and close it 10 times and 10 slightly different versions of “0” are reported even though the plate is physically closed. With the engine off, if I very delicately let off the gas, I can get the throttle plate to sometimes stick open at 5-15% (it is the assembly sticking because the throttle cable is loose). It’s not as bad as it sounds because when the engine’s running, the vibration allows it to completely close, but that can’t be counted on, as in “it’s all fine until it isn’t”). Cleaning it unfortunately didn’t fix it. Not sure whether to buy another used unit and take my chances, or buy a brand new OEM unit just so I know what I’m getting. [Then again, maybe not… nearly $800 from discount sites, and they come complete with stuff I don’t need. All I want is the housing, throttle, and shaft.] Anyone have one in good condition? These things are getting valuable – when I get this one off I’ll see how it can be repaired. A “fix” might simply be another spring, but it would have to be an OEM type spring, a helical type due to how the shaft rotates.

Before anyone mentions it, I don’t really want an aftermarket assembly because they typically run oversized throttle plates for hp bragging rights. That’s fine for drag racing, but when finesse is needed, having a smaller throttle plate makes it easier to modulate power mid-corner.

Anyway, the plan is to drive out to the desert one day this week.