Red Tornado

My idle problem has popped up its ugly head again, after having a month off of pure enjoyment. Idle drops and recovers about 10 or so times until it finally achieves a steady idle, after coming to a stop. It doesn't wander, its not high; it simply drops and recovers as I mentioned. Idle is set at 850rpms on the chip.

No vacuum leaks; its steady at 15".
TPS is steady at .53v.
IAC bore is very clean.

IAC was previously replaced, as the counts evidenced by TTS datamaster scan were all over the board, from low teens to over 100 counts when at idle, once warmed up.

The idle condition was perfect for about a month after IAC valve replacement. I went with an Airtex unit and not junk ACDelco.

Now my IAC counts at closed loop idle are in the mostly in 60's, and occasionaly in the 50's and 70's. Is this new Airtex unit going on the fritz, and that's what's causing the return of the idle drop & recover syndrome? Where should my IAC counts be at idle? Is it 10-40, or 30-60?

Or is my ECM unit (Borg Warner reman unit, installed for 2 years now) bungling up the feedback signal?

My o2 sensor data looks normal and reacts healthy.

How do I test?

zr1fred

How old are the injectors?

Red Tornado

FMS 24# injectors, approx. 7,000 miles on them.

mseven

I set mine right around 40 counts. When temps move say between 184-192 it will change slightly (a couple of counts).If you are at opreating temp. I don't think it shouldn't be moving that much. Sounds like it is getting out of range if you are seeing 70 cts. at 850 rpm. What else is happeneing when you see this? Timing moving also? Fuel pressure look good?

Red Tornado

static timing? its solid at 6* BTDC and doesn't move at all. total timing jumps around somewhat per datamaster scan. fuel pressure is steady at 44 psi.

at this early stage, i'm wonder if the IAC valve is out of range just enough to cause a bit of a rucous.

mseven

That's a good place to start, and doesn't cost anything. Bring it down to around 40-45 cts. On mine when ádjusting, I also notice that the total spark advance on datamaster or scanner will smooth out (less movement) when counts come down. IMO.

tequilaboy

What are your counts when rolling off throttle before coming to a stop?

This is typically controlled by the following table. (These values are from an 88 bcc ABTR)

Warm IAC Park Position Vs. Coolant Temp.

Deg C Steps
-40 145
-16 145
8 113
32 100
56 80
80 50
104 50
128 50
152 50

If the counts from this table are below the typical value when in rpm control, there will be some delay as the IAC transitions control from one mode to another and has to increase counts to keep the rpm near the target.

I would recommend setting this table very close to your normal iac counts when in a stable idle under the rpm based control for a given coolant temperature.

Another option if you can't change the tune easily, would be to adjust the throttle opening to get the best match with the table and adjust the tps accordingly to back to 0.54 volts or so.

In this example open the throttle plates so that you get around 50 counts in a steady idle. Of course, your tables may vary.

Red Tornado

If I'm adjusting the throttle plates, isn't this a false fix? It would seem to me that fooling with this is only adressing the symptom and not the cause. Idle was perfect after I replaced the IAC; if the IAC counts are out of range, would that not indicate same bad data feed from the ECM, and the ECM is actually the cause? Please don;t take this as arguing; I'm just trying to wrap my arms around this properly.

I'll be back in bit, I've got to look at the scan again to see what my counts are when "rolling off throttle", to answer your first question.........

mseven

Turning min. idle screw (opening blade) lower counts.

Tequilaboy, I didn't understand the source 88?
I know my tables are set up differently -30 =160cts and last 3 are 40 cts. forget the rest. What program are using to go in and 'see'all the tables?

Red Tornado

mseven, i do appreciate that advice, but forgive me for saying i'm not messing with min idle, as it will likely start causing other issues. i'm a stickler for addressing the cause, and in my layman's opinion right now there's something at fault that needs replaced.

mseven

I can understand, if any fault I would suspect IAC first though.

Red Tornado

tequilaboy, i quick sort of snapshot of values, as soon as i let off partial throttle:

rpms iac count
2025 89
1850 70
1675 62
1475 62
1025 62

idle 675-850 61-63

oh, and coolant temp is 181*F, closed loop operation.

edit: the faulty idle condition doesn't exist at cold start up & idle in open loop; it only starts acting up once engine is warmed up.

tequilaboy

Sorry M7, ABTR is the broadcast code or bcc from my stock memcal from my 88 4+3. If you look at the memcal, there will be a label with the bcc listed.

As far as tuning software, I primarily use tunercat, but also have TunerProRT. I also have detailed eprom disassemblies of 32 (based on bcc BUA) and 32B ( based on bcc ABTC) so I can hack in deeper than the typical editors will permit.

The table in question was copied and pasted from a tunercat text file (file->print to file ).

Regarding the problem at hand. I was simply pointing out that a mismatch can occur between the IAC park position table and the effect of the desired rpm table (the iac counts at idle). This can be due to any number of factors on a modded car, and may have not been addressed in a custom tune.

There's no harm in adjusting the throttle stop as long as correct tps volts are maintained at idle to keep you out of throttle following mode which will add counts based on tps position.

I run my throttle stop completely screwed in for the largest opening, then back off the tps to 0.54 v so I can achieve the maximum range of IAC control, then I adjust the park position table for a good fit to minimize any stumble or jumps between the tables or control modes. I adjust for maximum air, not the typical minimum air setting.

You may indeed have a hardware problem, but I suspect its really an IAC calibration issue.

tequilaboy

Ok, The 62 counts during coast down look very close to the idle values of 61-63. So it would appear that the problem lies elsewhere.

I was expecting to see a gap here, but that is not the case.

Spark advance would be where I would look next, if there are any big drops in the main spark table as rpm decreases, before stall saver spark comes to the rescue.

I try to keep the spark table as stable as possible in the low rpm rows, to avoid any weird spark/load related rpm cycling.

Red Tornado

the thing is, idle has been rock solid perfect for the year now that i've had my engine successfully modified, about 6,000 miles without incident. only recently the IAC trouble began, and I replaced it. That was a month ago, and the 4 weeks since has been perfect; now the idle drop (2-300 rpms) and recovery cycle about 7-10 times until it steadies once i'm stopped on the road.

do you see my IAC counts as being on the high side at idle, or is it normal? i have a datamaster file with 4 go and stop/idle episodes and each is a bit different in terms of the IAC counts when idle is achieved; as I mentioned eralier the counts can go from anywhere in the 50's all the way to the low 70's, after sitting at full idle.

Red Tornado

Ok when letting off partial throttle, i'm seeing a typical 40-44* advance drop initally to about 29-30* on average. Is this drop too large?

As I mentioned, I've had great drivability for a solid year.

One thing I just noticed, after a somewhat steady idle is achieved......the total timing jumps around from the low 20's to 32*. What in the world would cause this, and is this condition getting closer to the culprit? Probably a bad question, since the problem at hand is the drop/recovery rpms "cyling" once tps is 0%.......

tequilaboy

As far as the counts go, as long as you have sufficient range up and down from normal, and a good fit with the park position table, you're good to go, remember you have 145 counts to work with.

In my case, I normally see around 80-85 counts at 800-850 rpm and I have my park position table set up to match (here's an example from one of my recent chips)

Warm IAC Park Position Vs. Coolant Temp.

Deg C Steps
-40 145
-16 140
8 130
32 110
56 90
80 85
104 85
128 85
152 85

My car tends to jump to this table due to a noisy vss signal at stand still (relocated battery cable routing issue) so I mess with this area frequently.

As a side note: I'm also trying to tune my car specifically for smooth running at 8-10 mph in a 2nd gear idle with minimal cam surge, damn dirt roads, and this table directly impacts how fast the car will idle when rolling in gear.

tequilaboy

29-30 sounds reasonable to me, here's an example of my custom spark table for reference (might be hard to read):

Spark Advance Vs. RPM Vs. Load

RPM Load Value (LV8)
32 48 64 80 96 112 128 144 160 176 192 208
400 28.1 28.1 28.1 28.1 28.1 28.1 28.1 28.1 28.1 28.1 28.1 28.1
600 28.1 28.1 28.1 28.1 28.1 28.1 28.1 28.1 28.1 28.1 28.1 28.1
800 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0
1000 29.5 33.4 33.4 37.3 37.3 35.5 35.5 29.5 27.4 21.4 13.4 13.4
1200 29.5 33.4 34.1 40.1 40.1 38.0 35.9 32.0 29.9 22.9 16.9 16.9
1400 29.9 35.9 35.9 41.1 39.0 39.0 35.9 33.0 29.9 23.9 20.0 20.0
1600 29.9 35.9 35.9 43.9 41.8 41.1 38.0 34.1 29.9 26.0 23.9 23.9
1800 32.0 38.0 38.0 46.1 41.8 40.1 38.0 35.9 35.9 28.8 28.8 28.8
2000 35.2 40.1 40.1 46.1 46.1 41.8 40.1 40.1 39.0 30.9 30.9 30.9
2200 40.1 40.1 40.1 48.2 47.1 43.9 41.8 40.1 39.0 30.9 30.9 30.9
2400 40.1 40.1 40.1 48.2 46.1 45.0 43.9 42.9 39.0 32.0 32.0 32.0
2800 40.1 40.1 40.1 48.2 46.1 43.9 43.9 42.9 39.0 33.0 33.0 33.0
3200 40.1 40.1 40.1 46.1 45.0 42.9 41.8 41.1 36.9 34.1 34.1 34.1
3600 40.1 40.1 40.1 48.2 46.1 43.9 41.8 40.1 36.9 34.1 34.1 34.1
4000 40.1 40.1 40.1 48.2 48.2 45.0 43.9 41.8 38.0 34.1 34.1 34.1
4400 40.1 40.1 40.1 48.2 48.2 45.0 43.9 41.8 38.0 34.1 34.1 34.1
4800 40.1 40.1 40.1 48.2 48.2 48.2 47.1 42.9 38.0 34.1 34.1 34.1

tequilaboy

Just saw your last post. Spark in the low 20s may be trouble depending upon your cam.

Here's a normal spark table, note how load and rpm effects spark in the 600 800 rpm rows. This is what I have attempted to stabilize in my tune. Maybe a small change in load dropping you down to 20 degrees

Spark Advance Vs. RPM Vs. Load

RPM Load Value (LV8)
32 48 64 80 96 112 128 144 160 176 192 208
400 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 16.2 14.1 9.5 9.5
600 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 16.2 12.0 8.1 8.1
800 20.0 26.0 26.0 20.0 20.0 20.0 20.0 20.0 17.9 14.1 9.1 9.1
1000 20.0 32.0 32.0 35.9 35.9 34.1 34.1 28.1 26.0 20.0 12.0 12.0
1200 23.9 32.0 34.1 40.1 40.1 38.0 35.9 32.0 29.9 22.9 16.9 16.9
1400 25.0 34.1 34.1 41.1 39.0 39.0 35.9 33.0 29.9 23.9 20.0 20.0
1600 29.9 35.9 35.9 43.9 41.8 41.1 38.0 34.1 29.9 26.0 23.9 22.1
1800 32.0 38.0 38.0 46.1 41.8 40.1 38.0 35.9 35.9 34.1 28.8 22.9
2000 35.2 40.1 40.1 46.1 46.1 41.8 40.1 40.1 39.0 35.9 30.9 23.9
2200 40.1 40.1 40.1 48.2 47.1 43.9 41.8 40.1 40.1 35.9 30.9 23.9
2400 40.1 40.1 40.1 48.2 46.1 45.0 43.9 42.9 39.0 35.9 32.0 23.9
2800 40.1 40.1 40.1 48.2 46.1 43.9 43.9 42.9 39.0 35.9 33.0 23.9
3200 40.1 40.1 40.1 46.1 45.0 42.9 41.8 41.1 36.9 34.1 32.0 23.9
3600 40.1 40.1 40.1 48.2 46.1 43.9 41.8 40.1 38.0 35.2 32.0 25.0
4000 40.1 40.1 40.1 48.2 48.2 45.0 43.9 41.8 39.0 38.0 32.0 28.8
4400 40.1 40.1 40.1 48.2 48.2 45.0 43.9 41.8 39.0 38.0 33.0 32.0
4800 40.1 40.1 40.1 48.2 48.2 48.2 47.1 42.9 39.0 35.9 35.9 35.9

Red Tornado

tequilaboy, please forgive my ignorance with tables; i'm not at that realm at this point.

looks like i've got a problem somewhere else. this is a fairly minor issue, as off idle response is good (healthy TPS sensor), this is only an idling annoyance......which of course needs fixed regardless.