90-93 idle droop or stall issues
 

If you have a droopy idle, causing stalls when you clutch, especially with A/C on, your problems will be cured by adding a variable TPS.

After installing the vari TPS, my A/C off idle recovery is just like stock, with the A/C on it's not quite stock but is very good and very passable for stock. My idle recovery oscillations are all gone, as well as stalling problems. I drove 15 miles in rush hour stop n go with the a/c on without a single stall.

Now hopefully I can get all the closed loop boost stuff to work. Fingers crossed.

B

Were you using MAPdot accel enrichment before?

-Mike

mind sharing what you adjusted in settings after installing the tps?

Calibrated the TPS and adjusted the closed loop idle settings to work with my car (more settings: idle control closed loop settings). I will take a screen shot if you want to know the exact settings I'm using BUT they really need to be set on a car by car basis.

Have not gotten into playing with accel enrichment, boost control, traction control, or anything else.

B

I suspect doing this will greatly benefit me, as my lightened flywheel plays hell with idle recovery using the MSPNP base map settings

Was the condition you were having problems with when you tip-in to the throttle off idle, like starting from a stop-light or something? Or just having the idle sag when coming to a stop light or something?

For the off-idle response, accel enrichment will help, and if you watch what the MAP does when you just tip into the throttle, the MAP will go into the high load (60+kpa), really low RPM area for a bit before revs climb. If you don't have enough fuel in that part of your map, that can cause it to choke up, too. It can get into that same area when the revs are dropping to (or a bit below) idle, like when you put your foot on the clutch right as you come to a stop. I also found I had too much timing in that area which was causing the car to want to stall when it got into that part of the map.

-Mike

My issue is idle sag coming to a stop light, etc. Maybe that has something to do with it...I need to work on my tuning like crazy, over the whole range.

Yeah the problem is sag when coming to a stop, due to the MS having to recover from the shock of the throttle closing without the benefit of throttle position information. It causes bad droop, sometimes stall. If the ecu is able to recover, it causes oscillations until it settles down. This isn't a problem that you are going to experience as badly, or at all, with any of the 1.8 cars as they all have functional tps sensors from the factory.

Without the tps information, the ecu has to act reactively, where with it, it will react proactively and open the idle valve.

You are right though that too much advance at/around idle causes hiccups. But this is an idle valve issue, not a enrichment, de-enrichment, or time issue.

B

Did a lot more stop n go stuff this morning with the lights and a/c on. It was short, rapid bursts of acceleration followed by complete stops.

Not one stall. Idle recovery is much smoother, as close to stock as can be expected for a "race" ecu. Idle speed is stable. No oscillations. Much much better. I believe I can adjust my fuel underrun settings to work with the TPS as well, I'll look at that once my laptop is charged.

Also, the cold start this morning was also vastly improved. Perhaps it was the TPS, or the tweaked idle valve settings Jerry put in, or a combination of both. But since putting in the big injectors, I've had to wait about 15 seconds before touching the throttle, or else it would stall. This is no longer the case. Start up is basically perfect. And honestly, I never did play with my cold start up enrichments like I was supposed to.

Warm start up is better too. No hunting idle/idle oscillations as before.

IMO, this TPS mod is not optional.

B

Since it keeps coming up, I'm gonna sticky this for a while.

Update: Drove the car in a rainy rush hour yesterday. That means lots of stop n go, most movement in 1st gear with limited time in 2nd. Also because of the rain, a/c, headlamps, and wipers were on. So a pretty good load on the car.

No stalls.

so does the VTPS out of an automatic miata bolt right up to a 92 or willi have to swap out the throttle body and or hack up my harness?

Unfortunately, you'll have to swap the TB, as the shaft is different on the auto TPS. Connector is different as well, so you'll have to either A) cut / splice the wiring, or B) come up with an adapter.

Jeff

fwiw, the shaft of my automatic tps snapped a week ago and I modified a standard throttle shaft to adapt (with a dremmel, a cuttof wheel, a drill n tap, and a steady hand). It is very possible to add the automatic TPS sensor without swapping the whole throttle body, just a bit more work. All 90-93 throttle bodys apparantly have the exact same casting, but you gotta tap the sensor mounting points if using a manual casting for an Auto sensor.

I really hope this makes sense, its based upon my experience with 4 different throttle bodys: 90auto, 90manual, 91manual, 93manual

could you take a picture of the modification to the auto tps?

90-91 tps different from 92-93? (manual)
 

In my quest to source an auto tps for my manual 91 I was told by one vendor that the 90 and 91 had a variable and the 92-93 had just a switch - this based on his review of the schematics.

(he also said the automatic version of the 90-91 had a variable and a switch)

I am out of my depth when it comes to assessing this so I thought I would check here.

You need to tell us what vendor this is so we all know to avoid them.

If you are searching for the BMW TPS part numbers and info (like I was) you can find them here:
https://www.miataturbo.net/megasquirt-18/mspnp-faq-12239/

Hope this helps someone :)

Yes I was looking for just that (thank you). As I understand the post, the Bosch p/n's listed are effectively equivalent, both bolt-ons, same wiring?

The wiring is probably different, but I don't have experience in this yet.