Pulsing Idle Disappears when Idle Air Control Valve is Disconnected

[2knob]

So what does that mean?

I rebuilt the motor recently, with Atkins 3mm parts, silicone vacuum, HKS downpipe, PFC, and a few new parts. It started the first time, and needed no adjustments. It's run perfectly until a few weeks ago, when I took it down to work on the upholstery, pulling the stock radio/CD in the process.

I start it, accelerated warm-up is fine, but when at temperature, it pulses between 800-1400 rpm. I swapped the Idle Air Control Valve, same problem. I adjust the TPS (narrow=1, full=.44), through the PFC, but no change. Electrical loads and air conditioning appear to have no effect on the problem.

I unplugged the Idle Air Control Valve and the problem, along with the accelerated warm-up, disappears. It idles (without A/C) and runs as good as ever.

So where does one go now? What inputs contribute to the IAC actions?

Thanks for any help...

[David Jerome]

A lot of cars with a PFC that I have had idle much better with the ISC un hooked. Im sure if you get Chuck Westbrooks notes you can find something about that in them but I havent bothered to get that in depth. However, usually with the ISC un hooked the car does take a little longer to settle on idle once letting off throttle, nothing major but noticeable.

[2knob]

I'll probably swap in the stock computer and see what happens, but I don't believe it sould be related to the PFC as it had been running fine up to that point, even when I bought it (in terrible shape).

[Signal 2]

...What inputs contribute to the IAC actions?

Thanks for any help...

Would/could too much difference between any of the rpm settings for idle speeds (no load; elect. load and A/C) and the corresponding fuel cut on de-acceleration settings be related?

[2knob]

The PFC is set at defaults, but if I understood your comment, I set all the decelerations to 1000 and all the idles to 800, same pulsing.

[RXtacy]

The ISC valve could have gotten dirty, gunk tends to build up in the solenoid. Have you tried removing and cleaning with carb cleaner?

[dudemaaan]

did you adjust the air screw at all or the TAS?

[2knob]

The ISC valve could have gotten dirty, gunk tends to build up in the solenoid. Have you tried removing and cleaning with carb cleaner?

When I removed the ISC, it was very clean, and the one I replaced it with was very clean too. I would think if it was stuck, it would tend to act the same as disconnected (relative to the idle air screw). I'll have to take a closer look at it, and see what makes it tick.

[2knob]

did you adjust the air screw at all or the TAS?

I've tried the idle air screw fully closed, 1/4 open, and 1/2 open.

Now, what's a TAS? Everyone seems to know what it is, except me...

[2knob]

Would/could too much difference between any of the rpm settings for idle speeds (no load; elect. load and A/C) and the corresponding fuel cut on de-acceleration settings be related?

I went back to the beginning and disconnected the battery.

During the learning process, the PFC was fighting the pulsing and having some success, but it seemed to be most successful under the AC load. I raised the no-load idle to 900 (think I now understand what you were saying) and the idle smoothed-out. I lowered the idle to 800 and it's deceleration to 900 and still no pulsing.

Now the problem is, that's only masking the problem (probably better than running with the ISC disconnected), but the problem still needs to be addressed. Does this help identify the real problem at all?

[cewrx7r1]

There are several systems working together to stabalize the idle. They all have there own set of performance ranges to control. If any get out of the controllable range, then problems like this occur.

O2 sensor, air pump, ACV, cold start fuel map, fuel correction map, and base fuel map all work together to control idle AFRs. The O2 FB switch turns the O2 control it off or on. Running a RECALC also ruins this O2 system.

ISC, Throttle Adjusting Screw, Air Adjusting Screw, and Idle RPM settings control ilde rpms.

Idle IG Control switch controls idle timing which tries to fine tune the idle timing.

"YOU" have to learn what does what and how to adjust them to improve your idle.
But if you mod you engine to some undetermine point, no matter what you do, they will not work as Mazda desgined them to do. Then you have to turn them off and go to a manually controlled fixed idle. Most single turbo guys have had to do it.

With O2 FB and Idle IG control turned off, the ISC will work better. But then you will have to tune your idle and cruise AFR for best smoothness.
When I went single turbo, I did this and ran 550/1300 injectors with the ACV still working as a source of air to the MP/cat which is after the O2 sensor. My ISC worked fine at all three settings.

Then I went 550/1600 injectors, removed the ACV, plumbed the air pump output directly to the MP/cat, and removed the purge valve for the gas tank. After that, my ISC would only work on electric load. I checked eveything including cleaning the ISC solenoid.
I could not get it to work. I went full manual idle control.

[2knob]

Thanks Chuck, you should be a motivational speaker. You motivated me to send for your tuning notes.

Throttle Adjusting Screw = TAS... Just goes to show that you learn something new every day, even when you don't want to...

I reinstalled the stock computer on the cold engine. When I started it, it raced to about 3000 RPM, but settled to 1500 RPM after a quick blip of the throttle. After it warmed up, it's idling at 1100 RPM (no pulsing), with the TAS fully backed out.

Does this mean there is a small leak around the throttle plates, or will it pull that much air through the Air Adjusting Screw?

[cewrx7r1]

S1: I reinstalled the stock computer on the cold engine. When I started it, it raced to about 3000 RPM, but settled to 1500 RPM after a quick blip of the throttle.
A1: Sounds like you still have the AWS solenoid installed and hooked up. That is whay causes the short duration 3000rpm. It was to quicly heat up the pre-cat. Usless and bad for the engine.

S2: After it warmed up, it's idling at 1100 RPM (no pulsing), with the TAS fully backed out.
A2: Could be, but have you insured that the throttle is full closed? Improperly
adjusted throttle cable or cruise control cable may keep it from closing.
Stuck dashpot may keep it from closing. Bad hot wax rod/fast idle cam assembly may keep it from closing.

YOU HAVE to know the engine systems.
That is why I tell everyone, make section "F" of the Mazda manual your bible./

[2knob]

I haven't had a chance to do my book-learning yet, but the PFC AWS was less than 2000 RPM, didn't think 3000 was normal for the stock computer.

The throttle cable and cruise control cables have slack, dashpot looks good, and I haven't checked the wax rod/fast idle cam assembly, but don't expect them to be a problem.

I fully closed the Air Adjusting Screw and it's idling very nicely at around 840 RPM, adjusting for electrical load, forgot to check A/C. Shouldn't this, for all intents and purposes, completely rule out a vacuum leak?

Thanks..

[cewrx7r1]

If you have to fully close the AAS for stable idle, then the TAS is opened too much.
Close the TAS a little (1/8 turn increments) and reopen the AAS to fine the sweet spot. This way you have room to close the AAS in the future if so needed.

If you adjust the TAS, be sure to check the TPS voltages as they may now need adjusting.