dmyers

On my way home from work today, I experienced an idle problem and was just wondering what others think the problem might be. Once the car ('91 vert btw) got warm (it was also about 92 degrees outside) and I turned on the A/C (got it fixed today) and then pressed the brakes the idle dropped and the car stalled. I discovered that If I turned the A/C off (made for a blistering drive home), it did not stall when I hit the brakes, but it did come close... Also while I was sitting at my exit waiting for the light to change I discovered that with my foot on the brake, if I turned on the A/C and gradually increased the fan speed the idle would drop as the fan speed increased.

I came home and began making incremental adjustments to the idle screw and then romping on the brakes to see if it stalled (then took it out and dogged it for a little while) and worked my way to a point where it seems to be OK. I'm still a little nervous though. (There's nothing quite so terrifying as stalling on I-40 during rush hour in the Greensboro, NC construction zones.)

Could it be:

Vacuum leak
Just poor idle adjustment
Alternator
Timing
?
?

Any help would be appreciated.

Darren

91vert

Could be a lot of things. Does it idle fine when the A/C is not on? Does the idle fly up to around 3000 when the car is first started cold and then ease its way down to 750 at normal operating temp? Who did the work on the A/C.....Mazda? Did it idle fine before the work was done?

The BAC valve is supposed to bump the idle up when the A/C compressor clutch engages to compensate for the extra load on the engine. It may not be working correctly.

On my 91 vert, it idles right at 750 and when the A/C kicks on I hear the BAC click open. The idle jumps right up to just below 1000 and stays steady there until the A/C compressor kicks back off. Check the BAC valve operation using the procedure in the Haynes manual or the Factory Service Manual.

If I were you I would check all electrical connections under the hood and look for vacuum hoses that might have been disconnected or damaged. Anytime somebody is tearing things apart under the hood there is a possibility that they missed something during reassembly.

dmyers

A local place did the AC work. All it ended up needing was a little R-12 and some Oil.

It generally idles fine although once it gets warm it tends to dip kinda low sometimes. I think it might jump up to 3K idle when cold and then back down (I know it goes up but I haven't really paid attention to how high. I will in the morning though.) I can't really say whether or not it idled correctly before the work was done because there was no real reason to run the AC (other than to kill power and waste gas.)

I have been reading tonight and saw the BAC valve section, but the Haynes Manual says that it applies to only '86 - '88 models. I'll look at that tomorrow anyway though as well as your other suggestions.

Thanks,
Darren

TheBigOne

turn on all of your accessories 1 at a time until you have all of them on including stepping on your brake. turn on your inside fan BUT DONT TURN ON YOUR A/C. notice if your car idle gradually starts to decrease. if so its safe to say that your ALT might be a little weak.

dmyers

I checked this morning and it does go up to 3K RPM's before coming down to 750ish RPM's.

hugues

Keep us updated on this problem.
I have similar pb on 86 NA

Yours is a 91 so it is slightly different.

On series 5,
the BAC is very involved with electrical loads.
So, when at idle, if you put an electrical load on (like AC, healights, etc), the ECU will increase duty cycle of BAC to provide more air and raise idle speed.

Check if ECU signal makes it to BAC valve

Very easy to do,
just unplug the BAC connector when idling with no loads on, and see if the rpm drops. If they drop, the ECU connects to the BAC and it is good.

If you want to know more about idle problems,
look at
http://www.teamfc3s.org/info/articles/idle.html
or better yet get a FSM for you years car (free at http://www.fc3s.org/ under manuals)

hugues -

Salguod

The 89-91 do still have a "BAC" valve. Never trust a Haynes manual. You can download a copy of the OEM service manuals from www.fc3s.org

Under "How-To's" -> "Manuals" -> "89-92 Factory Service Manual" download the "Fuel and Emission Controls Systems - Non-Turbo" PDF file. The BAC valve stuff is on page F1-41.

If you know your compression is good and your injectors are clean, then it really sounds like you have a BAC Valve problem, a bad EGR Valve, or a hidden vacuum leak somewhere.

Make sure to look at all the vacuum lines running to all your solenoids valves to make sure that none of them have broken off. As you've probably read, the rubber vacuum hoses get hard, and the plastic solenoids get brittle with heat and age. The least little bump and the solenoid hose connectors break off.

There are a few of them right above the AC Compressor, so if the AC guys were poking around, they may have accidenly broke one off without knowing.

Good luck.

dmyers

OK. Here's my plan for my weekend of troubleshooting:
(I just bought the car last week so bear with me)

1. Change Air Filter
2. Change Spark Plugs
3. Add fuel injector cleaner additive (any suggestions on brand/type?)
4. Verify Timing is correct (I don't think it is, I get some backfiring when I rev it up to around 7K)
5. Check for Vacuum Leaks
6. Verify BAC Valve and ECU are communicating (is there any type of cleaning or whatever to do to BCV?)

If these steps don't work:
1. Drain remainder of bottle of Scotch
2. Rant and rave like madman
3. Pass out in backyard
4. Receive wicked massive sunburn
5. Be subjected to ridicule by wife.

Have I left anything out?

Darren

Salguod

Sounds like a typical weekend to me.

Josepi

Scratch #3.
Move #5->#1
6. Yes there is a cleaning procedure for the BAC valve....

dmyers

#3 scratched

Need to do #1 for my sanity since I just bought the car.
Will move #5 to #3.

Can you point me to the cleaning procedure?

Thanks
Darren

dmyers

Or are you suggesting to be subjected to ridicule from wife first and skip passing out in backyard....

dmyers

In case anyone else was following this saga and wanted a BAC Cleaning Tutorial.

http://www.1300cc.com/howto/how2/bac.htm

D