The viscious cycle....

MrVito · 03-24-2008, 10:39 AM

Ok, so my intentions for this thread is partially to put my thoughts down about this motor that is driving me nuts, and to hopefully get a bit of insight to my situation.

Background:

I bought my 89 TII in January, it had 231,000 miles on the original motor, a blown turbo, vacuum leaks all over the place, 4 blown shocks, blown coolant seals, hunting for idle, and a host of other small issues. My solution for this was to pick up a JDM TII motorset form a local reputable importer (JHot). This solved my tranny, turbo, and seal problems. I'm currently running the USDM ECU (370), and the car runs fairly well. With a few small issues still. It sometimes hunts for idle, no matter how often I readjust the TPS. It will sometimes idle ok, and other, seemingly random times, it will hunt for a bit before settling down. BAC, ACV, split air pipe, and air pump were all eliminated, and the JDM motor had no AWS on it. Rats nest has been removed and all extraneous vacuum nipples have been properly blocked and show no signs of leaks.

Right now the biggest issues are the hunting for idle, the idle sometimes raises about 500 rpm when the clutch pedal is pressed, and the car has trouble recovering after I let off the throttle. Like I mentioned before the hunting for idle tends to cure itself, but the recovery issue is what is really bothering me. The car is acting like it has an atmospheric blow off, it gets overly rich when I let off the throttle in neutral and tries to die. Since all vacuum and boost checks have shown no leaks, the timing has been properly set, all connections are solid, and the TPS is adjusted and in spec, the only thing I can see is a mechanical problem with the lower primary and secondary butterflies. I think I'm going to see if there is some way I can mechanically open them a bit more at idle and adjust the main primary butterfly down a bit to maintain idle at or below 1000 rpm. This is my thought for a temporary fix while I finish the work on my spare TB to eliminate the secondaries.

Now to eliminate any thoughts about the BAC removal, it was removed primarily because all of the wiring on that "leg" or the USDM harness was cracked and brittle, and for the most part was breaking off with the slightest pressure applied. I had to make a new line for the O2 sensor, since that seemed to be the only important one on that part of the harness. I'd rather have kept the BAC, and still may put it back on, but even when I did have it hooked up, I was still getting a BAC error code on the ECU.

So I guess what I'm getting at is, am looking at this from the wrong perspective? Is there something else terribly obvious that I'm missing? Am I just a hopeless n00b that needs a serious pwning?

One more thought, the other day I tried the JDM ECU (374), when I hooked it up, I had to raise the idle and readjust the TPS jsut to get it to run, and the timing was 20-25 degrees off. Easy enough to fix, but the idle with that ECU was still very rough, and it had a neutral rev limit of 4800 rpm. I didn't try driving it like that, it was mostly just curiosity as most people had told me the JDM ECU wouldn't even work. I didn't believe them and insisted on being a stubborn idiot and checking for myself. The JDM motor is a 1990 vs my 1989. Does anyone else with a 90 or newer TII know if the car does a 4800 neutral rev limit, or is that a known symptom of a limp mode? The US ECU has never given me a neutral rev limit, not that I make a habit of revving in neutral, was mostly just curious.

/end rant

RETed · 03-24-2008, 01:56 PM

If you want OEM type idle, you need the BAC valve.
It's probably the single most important component to getting the engine to idle nicely.
I've been fucking with my Haltech E8 idle control through the stock BAC valve, and I gotta give credit to Mazda R&D for doing a damn good job with the stock set-up.
The engines just do no like to idle cold.
The idle seems to stabilize once the water temps hit around 120F or so.

As you have found out, you can bump the idle up over 1,000RPM, and it's pretty stable.
Trying to get it to idle under that without the BAC valve is very difficult.

If your BAC valve wires were disconnected, they could've shorted by touching anything metal.
This is common where it blows the BAC valve power transistor in the stock ECU, which could be triggering your error code.

-Ted

MrVito · 03-25-2008, 10:22 AM

Thanks for the input RETed. I'm not at all concerned with the cold idle, I pretty much count on that being lousy. The hunting for idle issue is still coming up with the engine warm and idle set at 1100-1200 rpm, however, like I said before, it only happens sometimes. Mostly after the engine has been under load and is relieved, like when coming to a stop. It's just driving me crazy because this car is a blast to drive, and the body is in incredible shape, especially considering its age. I'm tempted to throw in the towel, sell her, and go back to S chassis cars, but I don't like the idea of being beaten by this car. I dunno, maybe I'll just let her sit for a few days and not think about it.

RETed · 03-25-2008, 01:27 PM

How bad is the RPM's cycling?

If it's going over 1,500RPM, then it's hitting decel fuel-cut, which is almost always TPS related.

If it's cycling lower than that, it's most likely an intake vacuum leak.

-Ted

MrVito · 03-25-2008, 03:21 PM

It's bouncing between 600 and 1300 rpms, but it slowly levels out.

03-24-2008, 10:39 AM	#1
MrVito The Newbie Join Date: Mar 2008 Location: Augusta, GA iTrader: (0) Posts: 29 Rep Power: 0	The viscious cycle.... Ok, so my intentions for this thread is partially to put my thoughts down about this motor that is driving me nuts, and to hopefully get a bit of insight to my situation. Background: I bought my 89 TII in January, it had 231,000 miles on the original motor, a blown turbo, vacuum leaks all over the place, 4 blown shocks, blown coolant seals, hunting for idle, and a host of other small issues. My solution for this was to pick up a JDM TII motorset form a local reputable importer (JHot). This solved my tranny, turbo, and seal problems. I'm currently running the USDM ECU (370), and the car runs fairly well. With a few small issues still. It sometimes hunts for idle, no matter how often I readjust the TPS. It will sometimes idle ok, and other, seemingly random times, it will hunt for a bit before settling down. BAC, ACV, split air pipe, and air pump were all eliminated, and the JDM motor had no AWS on it. Rats nest has been removed and all extraneous vacuum nipples have been properly blocked and show no signs of leaks. Right now the biggest issues are the hunting for idle, the idle sometimes raises about 500 rpm when the clutch pedal is pressed, and the car has trouble recovering after I let off the throttle. Like I mentioned before the hunting for idle tends to cure itself, but the recovery issue is what is really bothering me. The car is acting like it has an atmospheric blow off, it gets overly rich when I let off the throttle in neutral and tries to die. Since all vacuum and boost checks have shown no leaks, the timing has been properly set, all connections are solid, and the TPS is adjusted and in spec, the only thing I can see is a mechanical problem with the lower primary and secondary butterflies. I think I'm going to see if there is some way I can mechanically open them a bit more at idle and adjust the main primary butterfly down a bit to maintain idle at or below 1000 rpm. This is my thought for a temporary fix while I finish the work on my spare TB to eliminate the secondaries. Now to eliminate any thoughts about the BAC removal, it was removed primarily because all of the wiring on that "leg" or the USDM harness was cracked and brittle, and for the most part was breaking off with the slightest pressure applied. I had to make a new line for the O2 sensor, since that seemed to be the only important one on that part of the harness. I'd rather have kept the BAC, and still may put it back on, but even when I did have it hooked up, I was still getting a BAC error code on the ECU. So I guess what I'm getting at is, am looking at this from the wrong perspective? Is there something else terribly obvious that I'm missing? Am I just a hopeless n00b that needs a serious pwning? One more thought, the other day I tried the JDM ECU (374), when I hooked it up, I had to raise the idle and readjust the TPS jsut to get it to run, and the timing was 20-25 degrees off. Easy enough to fix, but the idle with that ECU was still very rough, and it had a neutral rev limit of 4800 rpm. I didn't try driving it like that, it was mostly just curiosity as most people had told me the JDM ECU wouldn't even work. I didn't believe them and insisted on being a stubborn idiot and checking for myself. The JDM motor is a 1990 vs my 1989. Does anyone else with a 90 or newer TII know if the car does a 4800 neutral rev limit, or is that a known symptom of a limp mode? The US ECU has never given me a neutral rev limit, not that I make a habit of revving in neutral, was mostly just curious. /end rant

03-25-2008, 10:22 AM	#3
MrVito The Newbie Join Date: Mar 2008 Location: Augusta, GA iTrader: (0) Posts: 29 Rep Power: 0	Thanks for the input RETed. I'm not at all concerned with the cold idle, I pretty much count on that being lousy. The hunting for idle issue is still coming up with the engine warm and idle set at 1100-1200 rpm, however, like I said before, it only happens sometimes. Mostly after the engine has been under load and is relieved, like when coming to a stop. It's just driving me crazy because this car is a blast to drive, and the body is in incredible shape, especially considering its age. I'm tempted to throw in the towel, sell her, and go back to S chassis cars, but I don't like the idea of being beaten by this car. I dunno, maybe I'll just let her sit for a few days and not think about it.

03-25-2008, 03:21 PM	#5
MrVito The Newbie Join Date: Mar 2008 Location: Augusta, GA iTrader: (0) Posts: 29 Rep Power: 0	It's bouncing between 600 and 1300 rpms, but it slowly levels out.