Rich3fan

Is it safe to assume that if the desired IAC position parameter in Autotap shows counts but the IAC motor position always shows 0, that the sensor is bad or there's an open somewhere? Should I be trusting what Atap's telling me? Thanks.

Rich3fan

Stupid question I rekon.

I'm going to take the throttle body off again tomorrow and pull that sensor out and see what's what.

Rich3fan

Okay. There was nothing obvious when I took the IAC off and looked it over. A bit of carbon buildup but that's it. Maybe I need to supply y'all with more info. Hopefully this will spur some suggestions...

I logged data while the car was sitting in the garage. I shifted in and out of park repeatedly (this is the point where I get the highest surge), increased RPM to 1000 while in gear to get a heavier load on the engine, while running at operating temp. My question remains, why am I seeing 0 counts of IAC Motor position with all other relative parameters causing Desired IAC counts to change:

Calculated Engine Load = 3.9%
Coolant Temp = 181
MAP = 10.6" Hg
TPS = 0.8 volts
Desired IAC = 66 counts
Desired IAC Airflow = 0.2352 oz/sec
IAC Motor Position = 0 counts.

I understand the PCM makes its decision to change the pintle's position based on RPM's, (all other conditions being equal) but hopefully this isn't a "chicken before the egg" scenario.

Hugger

iTrader: (21)

I noticed the same thing with mine tonight while doing some logging to tune my running airflow table. Hopefully someone that knows what is going on will chime in on this. TTT

Rich3fan

I don't know what tuning tool you have Hugger, but all I've got is the old version of Autotap. I wouldn't be able to change anything even if I did know what the problem is. I may be wrong, but since the IAC has only four wires for the two coils that the PCM uses to step the motor, I don't think there is any way to provide the PCM with direct feedback as to where the pintle is to begin with. I think it's looking at rpm's. I believe that parameter (in Atap) is bogus, and if I had a known good IAC I could prove it.

I think the general lack of response to my question is because people are trying to tell me that I should go buy EFI Live or something.

jimmyblue

iTrader: (11)

If you unplug the IAC connector and the idle
changes (like dies, or just becomes stable or
sags when you hit the A/C) then you can
conclude it's active. If it makes no difference
then something's up. If your car is consistently
on target for idle speed then the IAC must be
working (otherwise the speed will vary with load,
temp, in/out of gear).

It could well be that ATAP is looking at the wrong
PID (sometimes there are GM and SAE params
that see differently, or some just return null values).

Or you could just have enough bypass air from
leaks or drilling that the IAC doesn't need to
crack on. But that would be a big leak, in D with
A/C on.

With a large desired and zero actual there should
be a large trim value that absorbs the difference,
if this is a commanded discrepancy from learning.

Rich3fan

I unplugged the IAC connector and the idle didn't change. I did this after letting the motor warm up and go into CL-1. When the engine was still cold... OL-1 as expected. The PCM did eventually set a P0507 code which I think is to be expected, but even with the connector off when I shifted into drive the idle still surged. After this, I disconnected the + side battery cable for about 5 - 10 minutes then ran the idle relearn. What I think I'm going to do next is disconnect the + battery cable for at least ten minutes then start the car and drive it. I don't think the PCM is acknowledging the relearn at all.

Looking at all of the o2 sensors with Atap while this is going on tells me that there isn't anything wrong with the sensors or the cats. I see some wild mV numbers (never more than 1 volt though) at both sides of the cats, but for the most part, S2 < S1 on both banks. I'm also beginning to think that Atap usefulness has run its course and it's time for a change. It read the "idle high" codes, but when I tried to get the Freeze Frame data, it would lose connection to the car.

How's this for a wild idea: The idle surge is being caused by a faulty torque converter? Another thing I've recently noticed is that when I get into the throttle and the trans downshifts to where I'm turning more than 2.5K rpm's, all hell breaks loose in the engine. It backfired, stalled, idled really rough and was hard to restart when I tried this last Friday. If I drive at less than about 30% throttle, things aren't so bad.

I think I may just have to bite the bullet and take it to the dealer for a diagnostic test.

Rich3fan

Turns out I had two separate problems. The tech at the dealer where I've taken my car for 8 years told me the first problem (idle surge) was due to the polished throttle body. He said that by polishing it and knife edging the butterfly, the diameter of both changed which made a larger than acceptable gap between the two. This allowed more air than what already goes through the hole in the butterfly to enter; the PCM saw this as too much air, left the IAC at 0 counts and dumped more fuel. I said to him... if this WAS the case, why has it taken 5 years to show up? He didn't really have an answer, he only made a comparison to a customer's problem with something of an electrical nature. This sounds more like a mechanical problem to me, don't ya think? Something else he said which I did tend to agree with, when I told him it was suggested to me to disconnect the IAC while the engine's running to see if the idle speed changes, was that if you disconnect it, how is it going to get power to move the pintle anyway? The IAC is a stepper motor with two coils and four wires, of course it's not going to move. The pintle's not spring loaded, it's on a worm gear. That's not to say Jimmy that I disagree with your suggestion, but I think it can be said that the computer was reacting to some other condition. Where I flaw the tech's theory is his above explanation for the IAC always showing zero counts. The Desired IAC position IS showing and varying counts. Another flaw is where, instead of swapping in a known good IAC, he jumped to the conclusion that it was the throttle body because when he installed the new one (which cost me $315.00) and includes a new IAC, the surge stopped so end of story. IOW, it looks like he just shotgunned the entire assembly without first narrowing it down to one component, at my expense. $175 IAC vs. $315 TB with IAC. I told him I want the old assembly, and if I have a mind to do it, I may just swap in the old IAC and see what happens. Another thing... my advisor told me there's no return policy on IAC's because they're an electrical part. Once you buy it, you're stuck with it.

Problem #2: Misfires.

Advisor: You've got Autolite spark plugs installed, they're junk and may be why #7's misfiring. I think we should change them back to AC's.
Rich: Okay, but they're only a year old.

8 plugs and +$200.00 later... (see above return return policy)

Tech: It's still misfiring. You used to race it right?
Rich: Not since 2001 and I never messed with the rev limiter.
Tech: You may have a broken valve spring.
Rich: HUH???
Tech: We may have to pull the valve cover off to check. I'll run a compression test on #7, and try a different coil pack first.

Yeah, okay. SO, can someone tell me how the PCM checks for misfires, and can a broken valve spring be detected by it?

I think what we have here is a conspiracy. GM, because of their dumbass decisions (like dumping the F-body platform) isn't selling cars. They have to make money somehow, so they're pushing dealer service departments to sell parts. My advisor tells me that Autolite plugs are junk but AC Delco parts are great! Put 2 + 2 together, and what do YOU conclude? And do you think...

jimmyblue

iTrader: (11)

Since you now have a spankin' new TB and IAC you
can mix-n-match the parts (new IAC on ported TB)
and see about that. Similarly you could swap the
new butterfly plate on and set up the stop-screw
for dead closed, minus a RCH to test that element.

I'm not sure the IAC has any real feedback though,
in the "actual" position. The connector looks like it
doesn't have enough wires for a position encoder.
I think it just works from baseline reset, and maybe
the "desired" is the calculated airflow based position
while "actual" is this, plus RPM-based trim. Two
questions are, is the RPM above or below setpoint
and what do you see as trim (LTIT, STIT) values?

What happens if you try using real time controls in
the scanner to push IAC actual position? Can you
do this? Never tried, myself.

You "may" have a broken one of everything in the
parts book. Heh. Guessing, by the hour, what a deal.

How badly is #7 misfiring? Counts like onesy-twosey
are normal but more like popcorn, random. If one cyl
shows 10X the rest, consistently, then that's stark.
Plug wire, spark plug, coil, injector swap with neighbor
(one thing at a time). #7 is in an unfortunate position
(really all end-of-rail injectors, tend to accumulate
more silt in the screen than center ones).

At least it's better than trying to get at #8.

Rich3fan

Thanks for sticking with me here dude, I'll work on that this weekend.

Correct about the connector. The schematic shows wires only for the two coils inside the IAC. It kills me that GM has to make this such a complicated and expensive piece. Nature of the PCM maybe? The RPM's were above setpoint, if I'm understanding what you're asking correctly. The PCM set a P0507 code Wednsday night which is "Idle Speed High" The idle surge had started becoming progressively higher and more frequent as time went on.

I'm going to hook Atap back up on my way home from work so I'll look at the two values you question. What does the IT stand for in Short Term & Long Term?

Unfortunately the only tool I have is version 2.05 of AutoTap so I can't change anything. When I walked back to the shop, he was doing something to cause the idle to increase slightly with his Tech II tool, and it only occured to me after I got home that he may have been commanding the IAC. If that's true, then I'd have to believe that there really wasn't anything wrong with it. Like a dumbass I didn't look over his shoulder though.

Misfire counts are pretty high. During one count cycle I observed 84 misfires on #7. I've noticed an inordinate amount of misfires on #2 occasionally as well. Unfortuantely my only F-bod neighbor is LG Motorsports; I don't think they'll let me swap in known good on-hand parts, but I can swap around coils and wires from other positions so we'll see what gives.

Funny you should mention #8. I asked the tech how he gets to it. "From underneath, but it's still a bitch with the cat being in the way". Then he showed me the marks on his arm which gave me a warm and fuzzy feeling, ya know?

You're giving me plenty of food for thought Jimmy, thanks again. Next I'm going to on home, some beers, then start fiddling about. -Rich

Rich3fan

I did some testing Saturday night with Atap monitoring while I made some runs around the neighborhood. This included one WOT run, even though the TPS never showed voltage above 3.8 volts. What I'm going to show here are the conditions, including LT & ST Fuel trims, when I saw 26 misfires during one count cycle which occured after the WOT run:

Misfire Current Cylinder #7: 26
Engine Speed: 1654 RPM
Engine Coolant Temp: 192 degrees
Ignition Timing Advance: 39.5 degrees
Knock Retard: 0 degrees
TPS: 1 volt
Fuel Trim Cell: 4
LTFT Bank 1: 3.9%
LTFT Bank 2: 2.3%
STFT Bank 1: -1.6%
STFT Bank 2: -2.3%
STFT from o2 B1S1: -1.6%
STFT from o2 B2S1: +1.6%
Desired IAC Position: 132 counts
Desired Idle Speed: 550 RPM
IAC Motor Position: 0 counts
Fuel System Status Bank 1: CL-1
o2 Sensor - B1S1: 850mV
o2 Sensor - B1S2: 738mV
o2 Sensor - B2S1: 830mV
o2 Sensor - B2S2: 685mV
All relevant monitoring sytems: Complete

As far as problem #1 is concerned, I think it would be best to leave well enough alone. With what I'm seeing above, I think problem #2 would be anything BUT a broken valve spring. I agree that it's more like an injector, wire or coil. What do ya think? Thanks.

-Rich

P Mack

iTrader: (6)

Could be, but not in your case since the desired IAC is more than 0.

BS, the pcm didn't leave the desired IAC counts at 0.

To answer your question, STIT and LTIT are short and long term idle trims. They are an airflow (g/sec) correction that are used to maintain the right idle rpm. They are determined by your rpm being above or below desired for a certain amount of time. The trims are translated into a desired IAC position.

You're misunderstanding the "unplug the IAC" test. Obviously it can't move if it's not plugged in. The point is to see if it behaves different when it's unplugged. If it behaves different, that means it was moving when it was plugged in, you just couldn't see it on the IAC position log. That may be the only way to determine for sure if the IAC is moving when plugged in.

P Mack

iTrader: (6)

Is that latest log with the new IAC? It's possible that autotap just isn't logging iac position correctly.

Rich3fan

It's possible that I didn't understand everything he was explaining, but nevertheless he blamed the surge on the modified TB. I'll try to get a clearer picture when I'm back there.

Autotap version 2.05 doesn't include those parameters, but there is a parameter: "Desired Idle Air Control Airflow", that measures in oz/sec, and showed .396 oz/sec

Things behaved the same way whether or not the IAC was plugged in (i.e. Idle still surged when put in gear, air conditioner turned on, trans shifted back into park). Plugging the IAC back in and not running the relearn didn't seem to make any difference either. I think the tech exercised the IAC with his Tech II tool and that's why I heard the idle picking up when I walked up to him.

I'm probably sounding like a defeatist, but I'm just going to let that sleeping dog lie. The new TB, which includes a new IAC is working, and unless my service advisor is pulling my chain, swapping back the old IAC is a moot point because they won't take the new assembly back anyway.

Yes it is. New TB with the new IAC. My focus with that log file was on the misfires situation. I played back the log file and stopped when I saw the 26 misfires on #7. The things is, I don't believe that particular time slice has all parameters synchronized with that misfire count. I mean, you can stop playback then single step one frame at a time, but I don't think that garantees that all other readings will show accurately during that frame.

I think I mentioned that I feel my ATap scan tool has pretty much outlived it's usefulness, so it's either buy EFI Live or HPT, or depend on someone with a more comprehensive tool. I certainly appreciate all the helpful input, but I don't think it's possible for me to get y'all the information needed to make a more conclusive decision. Thanks.

jimmyblue

iTrader: (11)

The way I make out the idle scheme you have a desired idle
airflow (from the Running Airflow numbers) that is mapped
to an IAC position (effective area vs IAC counts) to make
the baseline idle position, and then over that the PCM lays
the RPM target loop which it hits by trimming. If idle is high
and trims are negative (LTIT) and counts are zero then it
seems likely there is -some- source of bypass air into the
manifold that has made the thing trim low and fail to get
to idle target (Idle Speed High code). It might or might not
be within the TB; could be a damaged / missing TB-manifold
O-ring gasket, or something in the vacuum hose, or just
loose manifold bolts etc. Might be time to step back,
unplug the IAC, break out the propane / carb cleaner and
go leak hunting.

Maybe the leak is around #7. Which is also at the back
of the manifold where the MAP sensor and vacuum fittings
plug in (and hard to shoot carb cleaner at, very well).

Rich3fan

What'd he say?

"TB-manifold O-ring gasket." Hmmm... I can tell you that the gasket was in place everytime I pulled the TB off, but I can't say with confidence that it wasn't damaged. The tech gave me back the TB and spark plugs, but not the TB gasket, which he did replace and charge me for. Hmmm... I've been known to be a paranoid person (or is overly skeptical a better word?) but everytime you guys suggest something, I just become that much more suspicious of these guys at the dealer. Am I being naive as well?

I'm getting the impression that I shouldn't let this Idle issue die afterall, so let me ask two new questions: How fragile is the TB gasket (i.e. can it's properties change or flatten out after a lot of TB reseats?), and do you agree or disagree that ATap v2.05 is a worthwhile tool to keep in my arsenal.

This is starting to get my juices flowing.

P Mack

iTrader: (6)

If it was a vacuum leak I would expect desired and actual IAC counts to be low or 0. Also I would any misfires to get better, not worse, as the throttle opens wider. What is your desired IAC at idle with the new tb?

A few more questions. Did you do any work to your car before these issues started? Are all your ground connections good? Are your pcv connections secure? What is your TPS voltage with the throttle closed?

Rich3fan

In Nov of '05, I had a fuel injector service and fuel filter change done. At the beginning of June of this year I had non-related work done (oil change because I stripped the FREAKING drain plug, fog lights replaced (service advisor told me I'd have to drop the front clip in order to change the bulbs myself), and a state inspection, which includes the emission test. All tests passed. When I went back to collect my car, my advisor, Scott told me in passing that my throttle body was dirty. Neither of us persued it, but when I got home, I decided that since my days of weekend mechanic were about to resume, I figured cleaning things up around the intake would be a good place to start. Returned from Autozone with shiny new can of STP Throttle body and injector cleaner and went to work. Instead of just spraying it into a running motor, I thought it would be safer to pull the TB off and spray it down real good then wipe with a shop rag. The TB was VERY dirty, and a theory I had, which I should have mentioned sooner was that the grime was helping to create a bit of a seal, enough to make the PCM think there was no problem with getting too much air, although you've debunked that idea. But that's when the idle surge started. Now, I talked to the tech who's been doing the troubleshooting, and I asked him if any harm could be done if the cleaner got into the IAC; he said not really. The troubleshooting procedure I got from Scott when I asked for the IAC's electrical schematic indicated otherwise. I didn't spray directly into the bypass area, in fact I did the best I could to avoid it and used a rag and my finger to clean it up. I didn't have the right torx bit at the time else I would've taken the IAC off.

I just now looked at the components around #7 including the injector and coil pack and it doesn't look like it would be too difficult to disconnect and swap #7 & #5's coils, but I can barely see the injector, so I don't think I want to mess with that.

It's kind of hard to give you a consistant Desired IAC position count because it seems to fluctuate quite a bit at in-gear idle, but as best I can tell it ranges between about 46 & 62 counts.

Battery ground is good, but I'd have to feel around before I could conclude that all other ground connections are secure. TPS voltage when closed is .6 volts. It was .7 before the tech changed it. He let me know that he did that but didn't tell me why. The set screw change did slow the idle though. RPM's are very close (~558 rpm's) to desired which is 550. I also, after all this started, pulled the PCV valve out and cleaned it by soaking it in gas, then spraying more TB cleaner in it. I gave it plenty of time to dry before re-installing ( what a bitch THAT was!).

Thoughts?

V6 Bird

iTrader: (15)

SOunds like you need to find you a new dealer...and a new tech to work on your car and diagnose it. sounds to me you are stuck back in the Shaner days..hahah

In all seriousness Rich, (beenfetchedlately here BTW ] have you ohmed the wires to check them for resistance? Shoot me some PMs with the specs on the car...i cant remember if Shaun did a cam in that car a while back or not. Been too long ago since ive seen you of the car...

Injectors clogged normally wouldnt cause a misfire like your seeing. Ive seen cars surge though because of that and plugs being doused (sp) with fuel and then it misfires because its basically fouled then and only hits every other cycle or so.

If you need someone to get down in there and lend a hand...I can help its just that im not all that close to ya...

Swap the coil packs first. Then test the ohms on each of the wires. The injectors are quite easy as well and would take about 30 minutes to move to another location...

P Mack

iTrader: (6)

Are you sure your pcm even know's the throttle's closed? I thought the tps voltage had to be below 0.4 V or so for the pcm to apply the idle corrections. It's to bad you can't log stit's or you could see for sure if they're updating. What fuel trim cell are you in at idle? What is your TPS percentage?