Welp, after suffering for months over idle issues, and having no decent control over a set idle-- i was in search of final ideas that could lead to what went wrong.

I had done the TB mod, emissions removal, BAC remova, and aux/vdi port work all during the same downtime. I had confidence in the TB mod, that it was done to whatever spec we could call good. The aux and VDI were pretty much unrelated.

The only thing I hadn't done in attempt to get idle back was in reinstall the bac. I was apprehensive at first, but I knew what it had come down to.

So I went searchign in storage for the BAC. I found it and headed to NAPA for vac line, coolant line, some carb cleaner and gasket maker.

When I got back home, I removed the block off plate, found some of the matching bolts (originaly studs IIRC, couldn't find them). Iground off the old gasket on the BAC. I cleaned out the BAC and went to work. I had it installed within about an hour (had to remove the manifolds to get to the rear plate port.)

I plugged everything back in and went to start the car. Isntantly started right up and reved to 2krpm. I noticed the CEL was on, and then she smuttered and held a 25-50rpm idle, barely. I knew somethign was up when I went to give it gas to keep it runniing, and stomping the pedal down did nothing.

So I shut her off and take a look. Heh... this is what you get in a hurry. So I missed hooking up both the TPS wire harness AND the throttle cable. LOL, no wonder **** didnt' work right.

I went back in, started it up, she reved to 2k for about 5 seconds, dropped to 1200 steady. I jumped out and adjusted idle down to 900. Its solid... INCREDIBLY SOLID. For the first time in 4 months, I can rev it, and it will come all the way back down to idle and hold. It doesn't go below 900, it doesn't sputter out when you idle, it is SOLID.

By far the best driveability mod I have done since I removed the P/S rack.

there are picts, but they arent interesting.

The only picture you guys might not understand is the 3rd. Its a picture of my rework for the Injector bleeds. Originaly the line had to go before the TB plates. With the removed vac rack, this turns into a PITA! Anyhow, this little doodad plugs into one of the ports on the intake elbow and gives me 4 ports before the TB plates, right near the bleeds too. It was made by hacking up part of the original vac rack.

 

Good to hear! My idle isn't too bad, but I'm still planning to clean the BAC at some point here. Nothing's nicer than having a rock solid idle IMO. A solid 750rpm rotary idle is one of the sounds I've come to love. Mine does it... most of the time.

-=Russ=-

 

so this is probably whats causing my unstable idle, 1 day it idles perfect at 900 the next day idles at 1300, but i put the fd uim on my car so there is no way to put the bac back on

 

I saw the word "Fram"!!!

 

Oh man, don't get us started on the "What's wrong with Fram" thing again, lol...

Congrats, Kenteth- glad it worked out for ya...If you want to see what the BAC's doing during drives, hook up a meter to the output pin on the ECU (to ground), and you'll be able to tell when it's energized, and what kind of duty cycle she's running (interpolation from the voltage drops from 12v), during different transient events (idle, electrical loads/lights on, decel, WOT, etc...)

 

Nice, I'll have to take mine off and give it the old clean treatment. What color RTV would you suggest for the gasket?

What is the normal idle anyways? Mine idles at 2k until it's warm, then down to 500rpm and never goes above/below.

 

Mine idles happily at 800 without the BAC, the only time it drops is when I'm turning a corner, have the lights on, the blower on, and my foglights. (still got PS)

 

I wanted to use copperII-ultra from when I did the manifolds, but apparently it got misplaced/used. I found some RTV red and used it. I think it was the same stuff that I used on the BAC blockoff anyhow. Works fine, infact I had to pry the block off plate off it was holding so tight.

 

yeah lol i remeber how she almost died going into parking lots when u picked me up sonicrat. mine seems to do the same, but i put the idle back at 900rpms and the only time i see any problems is when i first start it. about a minute of warming up she's back in action. and then i still have the boost problem. good to hear u like ur idle though keneth.

 

The GTUs suffers from a couple of vac leaks, which I've finally taken care of. Now it idles happily, drops to about 600 when turning with all the accessories.

 

Idle problems can be a good indication of intake vacuum leaks.
The 13B does idle merrily without the aid of the BAC valve, if you have absolutely no intake vacuum leaks.
I bet the reinstallation of the BAC valve is just masking this problem?


-Ted

 

And no A/C...

 

It is definnately a possibility. I also had bouted a new air pump for the aux ports that I had mounted. I ran new lines for them and the VDI. I bought some extra line so I could hook the FPR solenoid back up. I did find one cracked vac cap. The nipple on the underside of the TB bad been cracked and was just barely holding on. I did replace it. i didn't think that one nipple could have caused so many problems. Either way the car is running *much* better now.

 

good to hear that. how much vaccum do you pull?

 

My thoughts exactly, Ted. I have no BAC and the TII idles as solid as can be after eliminating all vac leaks. I have no PS, but I do have A/C and it doesn't hurt the idle much at all.

-Joe

 

Overdriven- do you still have the air bypass solenoid & valve on the car? I think for heavy loads, the ECU doesn't use the BAC, but instead just energizes that AB solenoid, which routes more air in than the BAC ever could. That's why there are A/C switch "on" and power steering switch inputs to the ECU, so it can activate that sucker. I've still got it on my car, but since I don't have A/C or PS anymore, I doubt it energizes much, except for AWS...

 

Yeah, on my 86 I replaced all Vac lines and Thermo valve and it improved idle significantly. On my 87, I haven't yet torn into that problem. I'm going to replace all those lines as well...

 

23HG on rev decel. right around 15 at idle

 

i'm getting about 14-15 at idle but my motor has a medium streetport.

 

Quite frankly, I can't understand anyone's fascination with removing the BAC. It's there to allow the ECU to control the idle. What do you gain in removing it? Nothing. What do you lose? Lots of stuff. So why not just leave the damn thing on in the first place... FWIW, my car has always had a BAC and full emissions equipment. Only now since I am going standalone do I not have a BAC, but I have seriously considered retaining it. However, since the only external load on my engine is the alternator, I can get away without needing it.

 

ditto

 

Well for what that would be worth, I too have removed ap,ps,ac. I didn't know what the result woudl be of removing it and hence I did. I consider it a learning experience and if I had to do it over again, I probably would have done the same just because it really helped me learn how the BAC works and what it serves in the system.

BTW, I thought microtech (or was it haltech) had a control system for air injection?

 

I did not remove PS/AC/etc. My car never had it (base model). The major problem is that new owners seem to follow the "advice" to remove it without understanding any of the consequenes.

The Microtech has a BAC option, which I may need. First I'm going to try without it though, since I'm making a custom upper intake and I would like to save the trouble of fabbing a BAC mounting point. If I find that I can't live without it, then I'll install the BAC.

HOWEVER, since most people who remove the BAC don't have the slightest need to do so, nor any idea of the result...

 

the BAC is not the ONLY means for the ecu to adjust idle.

the pressure sensor serves some role in this too. i know because i dont have my bac and the idle will slightly dip from 800 then rebound when i turn on my headlights. i belive this shows the sensor detacts the increased load and the ecu respdonds (only slightly perhaps) and manages to return the idle.

however ther is very little the ecu can do if it doesnt control thethrotle and thus the intake air, which is why the bac is needed for higer loads like the p/s and ac.

 

Also have the "unstable idle" where it can be:
- 750rpms rock solid
- 500rpms when warm for no reason
- 500 rpms on an incline
- 500 rpms & stall when driving & not warmed up
- hunting with A/C on
- rpms drop with A/C on
- rpms increase with A/C on
- rpm drop is "cushioned" with A/C off
- rpm drop is not "cushioned" with A/C on - occasionally stalls

So far I've:
- set the TPS within spec
- verified BAC clicks with 12volt source
- reapaird ACV diaphram leaks (except the 3rd anti-burn air diaphram, it's inaccesible)
- verified vacuum actuators

With the RPMs not being constant, replacing all vacuum lines is all I can think of to do next (vacuum lines look ok now). Shouldn't be any air-leaks in between the MAF & TB, but that's kinda hard to verify. Also should re-set the idle when it's fully warmed up.