BluFBdy

iTrader: (1)

So randomly my car likes to idle higher than usual around 1500-2000 rpms, when this happens i do the good old IAC cleaning and tps adjustment which usually fixes the issue.

Pulled my IAC, cleaned it out and used lithium grease on the pintle, put it back in and reset my minimum air, my tach is iffy so ive always just set the screw to the farthest out where it will idle without choking out. put it back together started it and it was fine, idle was at around 1000 which isnt ideal but its better than nothing. shut the car off, started it again 2000 rpms.

So i broke out my fluke and checked my TPS, .55 volts closed, 4.23 at WOT, normal. ran it through the range and it increased properly no jumping or sticking, decreased the same. TPS seems to be in good shape.

Broke out the carb cleaner and cleaned the hell out of my TBI, nothing too major in the IAC passage just small buildup, no chunks or crud one shot of cleaner made it shine, sprayed down the whole tbi to clean off that light brown crud. Tried the IAC reset again, 1000 ish idle. shut it off and started it again FREAKIN 2000RPMS!!!

SO one more time, broke out my timing light and checked it, dead at 0*. Reset the IAC, without relying on the tach i just adjusted it until the car was barely getting enough air, just enough to run, shut off the car, pulled the paperclip, plugged in the IAC. Same thing. low idle then ridiculously high once i put it back together.

WTF is going on here? Im gonna lose my mind. The IAC is reacting the way it should when i look down the passage way, hit the gas it sucks in and moves back out when the idle drops.... im at a loss ive done a full TPS,IAC, timing check and TBI cleaning but the car keeps giving me the middle finger.

I've sprayed around the vacuum hoses and around the base of the tbi/ intake seating area and I can't get the idle to change. What I don't get is why it would be fine during the reset and one start after but the second and following starts it will idle high again


Help??

Ronny

iTrader: (1)

TB base gasket? Apparent VAC leak. Hose cracked?

BluFBdy

iTrader: (1)

Visual of the base gasket looks ok, sprayed carb cleaner with no idle change, is there something better I could use? Ether? Anything like that? If its a leak I gotta trace it somehow but carb cleaner didn't help

Ronny

iTrader: (1)

propane/map gas

BluFBdy

iTrader: (1)

So use a torch without lighting it?

Ronny

iTrader: (1)

correct

BluFBdy

iTrader: (1)

well i found one vacuum leak but nothing big enough to make the idle any better, my issue is when i do the iac reset it runs fine, then the first start right after it runs fine still, then the second start after and on it will run at a high rpm. If it were a vacuum leak giving me these hassles wouldnt it do it at all times? During the reset and immediately after? idk what i did tonight but i had thought i fixed it, on like the 7th start it went to 800 rpms which it normally idles at then about a minute later it climbed up while i was standing in front of the car.... im getting tired of this tbi gremlin.

BluFBdy

iTrader: (1)

found an odd bit of behavior from the IAC.... not sure if its relevant or not but just go with this:

When i jump the aldl and run the IAC all the way out, unplug the iac and start it, it idles properly.

Shut the car off and remove the jumper, plug the IAC back in, start it again IAC has not moved, its stepped all the way out, idle is PERFECT.

Shut the car off again, IAC retracts all the way, start the car again and the IAC doesnt fully extend to where it was before and the idle is at 2000 rpms.

Im not sure of the normal behavior of an IAC other than it adjusts itself constantly, but ive read about adjusting the pintle length, ive never done that myself ive always just run the pintle all the way down by hand and it was fine did the reset then it worked, i just replaced the IAC last night and it didnt help my idle, unplugged the IAC and it revved higher, so the IAC is working but...not the way it should?

Please advise on this

Ronny

iTrader: (1)

Did you or prior owner rewire the IAC?

I would plug the IAC passageway temporarily and see how it responds. I did so temporarily when one of my two IACs stuck wide open. I used a gob of hardened silicone sealer in a corner of a small baggy. foam earplugs will work too.

BluFBdy

iTrader: (1)

Oh no I've had this thing for 5 years now and I've never had this problem, ill try plugging the port when I get home today, when the iac closes the hole in diagnostic mode it idles perfectly, I just don't know where to go from here, if I plug the port and it idles fine what steps do I take after? One always been big on cleaning the iac and the port out this is the first time I've ever had this issue, I'm gonna hunt a bit harder for vacuum leaks becasue if there's a good sized leak comparable to the air let in by the IAC it would make sense that closing it makes the idle fine. I don't hear any hissing and haven't had the greatest luck with Carb cleaner, I'm gonna hook up my gauge to it and see where its at

Ronny

iTrader: (1)

OK then no vac leak. And you never rewired it. This is puzzling. I would go to JY and see if you can pick up an IAC. I wonder if it is shorted internally. Opening when it should close.

Something is telling ECU that it needs to open IAC when not needed. Temp sensor?

I would obtain an ALDL cable or build one, down load win ALDL and witness the steps IAC is commanded on warm engine. It may also show you stored codes if a sensor malf.

BluFBdy

iTrader: (1)

No codes, the iac is new but Idk if its good, I just don't get why the iac isn't responding properly, it will sit with the head of the pintle half way out of the hole, then when I shut it off it will extend fully and push out the hole all the way then retract like usual

Ronny

iTrader: (1)

I never messed with the mechanics of the IAC but I wonder if the pindle can be set to proper static position. Like does an IAC allow you to "screw it in and out" the pindle that is. Is it threaded? I read never energize it outside the TB as it will discharge the pindle. But if you measure its static lenght maybe it can be extended by turning pindle to allow it to seat further.

Cold engine key on it should retract to about 180-200 steps. then as car warms to 180D++ it should be at 5-20 steps. Mine is at 0 steps as my TB blades may be a bit open(cap is removed). A datalog will show only the commanded not the actual from what I was told.

BluFBdy

iTrader: (1)

The adjustment was my question I've read about it but Idk what the iac does when its off I just know it dissapears when its pulled back, Idk if it bottoms out or only moves a certain number of steps

Ronny

iTrader: (1)

Mine is set to retract 200 steps. Not sure if that is max but in my def file 200 is maximum I recall. For reasosns I am unclear as to why my initial fast idle is not fast. If I start this AM cold 50dF it idles smooth at 750 rpms then every 60 sec it moves up 100rpms until it is like 1200 then gradually drops to commanded idle speed 750 after it hits 160dF. . this is a 7.4L Tb on a 350 cid.

BluFBdy

iTrader: (1)

Question: when i unplug the IAC while running the idle is supposed to increase right? im not getting a difference is it possible my new IAC is bunk? It was replaced for the same issue, actually i replaced it because i snapped the threads on it but thats a different story, ive looked in the port its clear, when the car shuts off the IAC extends all the way into the port and pulls back in, so range isnt the issue, i tried unplugging the battery to reset the ECM but that gave me no help, checked my ecm grounds and theyre all good also im freaking lost here.

As far as the counts go Vader has posted 10000000000 times that they dont verify an IAC is good, just that the data going out is, im getting my buddys aldl here tonight so i can see if the data going out is good, if its not i get to hunt down an ecm, its a stock car minus the exhaust and ive NEVER had an issue like this.

BluFBdy

iTrader: (1)

This is a video of whats going on, click it and it will take you to my photobucket to watch it

BluFBdy

iTrader: (1)

Ive run a datalog for this if i could get someone to look at it for me i would appreciate it. Im new at datalogging and all however im not seeing anything weird on the charts UNTIL i shut the car off and start it again, so ive got the video of the problem, and a datalog showing the ECM side of the running, i reset the minimum air, plugged my laptop in, then started the car 750 RPMS!!! shut the car off and restarted it at the 1 minute mark and 1250 rpms! >_< im gonna rip this motor out and throw it off of a cliff

ex-x-fire

I'd do a continuity check between the iac connector & the ecm connector.
Also check the ecm (& all other) grounds carefully. Some of these are at the back of the heads & are tough to get to.

BluFBdy

iTrader: (1)

I don't see what a continuity check would do in this case, its operating just not properly, broken continuity would mean it wouldn't move at all, and it would have shown an error in tunerpro and/or thrown a code for IAC. The grounds are good I checked those first, and if my ecm ground were bad it would have blanked my eeprom out.

ex-x-fire

Did you do a resistence check of the cts when its at operating temp?
Is the cts in the stock location? I've seen guys put sensors & switches in those t stat housings (w/ the 2 pipe fittings), they only read right when the stat is open.

RBob

iTrader: (1)

My money is on a leaking base gasket. They dry out over time and start to leak, doesn't take much to get a high idle.

As for the tach reading high (from DFI & ECM board thread), see the sticky's at the top of the Electronics board here. The fix is simple.

As for why after an IAC minimum idle setup the idle RPM is OK. The IAC is closed when the engine is started. So the ECM will only open it to maintain a minimum idle speed.

Then at key-off the IAC returns to the park position. On start up the IAC will close down to get to the maximum allowed idle RPM. Which until the engine is fully up to temperature can be quite high. This is important to understand. Until the engine is fully up to temperature the ECM won't fully control the idle speed.

It will maintain a minimum speed to prevent stalling. But the actual idle speed only has an upper limit, not a "hold idle at this RPM." So the engine can idle high, and is allowed to. This is usually seen when a lower temperature thermostat is used.

RBob.

BluFBdy

iTrader: (1)

Cts is in a stock location. Did a resistance check at operating temp and its within spec. The datalog is showing a number which is dead on with my gauge (aftermarket gas filled temp line) my only hang up is my inexperience with tunerpro is killing me because the datalog shows the temp in a number on the graph but no line is present
I swapped ecms with a prom I burnt, only thing I changed was the EGR function and vats which had no effect on my idle so I know the ecm isn't to blame

Vader

Your video shows the IAC responding normally on startup and during operation. The retraction on throttle open and slow extension is part of the stall saver programming. Pre-setting a pintle length on the IAC only assures that the pintle doesn't get crushed into the seat when the unit is installed. When you see the IAC extending and retracting on shutdown it is finding its "home" and will do this every time, so setting to a specific pintle length is unnecessary except to prevent damage as described.

The idle RPM (by sound) does not seem inordinately high, but I don't know the coolant temperature nor intake air temperature. If this condition exists when everything is fully warmed and for more than about 20 seconds of running after startup, the ECM may not be commanding the optimal pintle position.

Time from start and temperatures will affect the IAC desired position, as well as gear selection on an auto trans car. There may be other conditions which might add steps to the IAC, such as AC request.

It sounds as if the IAC is responding to commands from the ECM as it should, so determining what the ECM is commanding with the engine fully warmed may be crucial.

I'll agree with Ronny that watching the commanded IAC steps/counts could be revealing.

1987bucket

Did this High idle issue get resolved?

BluFBdy

iTrader: (1)

yes, but i dont recall what it was, 12ish years is quite some time, pretty sure i was using the wrong mask during this, that engine is looooong gone now

1987bucket

yea figured it would be a long shot. I just got mine running and it’s doing exactly the same thing.reset iac and then turn it on runs fine when shut off go to start again and super high idle.

Schurkey

Connect a scan tool, verify EVERY sensor and computer output.

If you've dicked with the base idle screw, re-set it using the service manual procedure.

1987bucket

Have done the base idle reset along with iac reset. New cts,iac, checked over and over for a vacuum leak
checked ohms on tps. new Tbi base gasket the car sat for about 8 years before I got in to it. I haven’t used a scan tool yet I went over the basics to get it running again.

78camaroguy

Did anyone else figure this out? I’m on my second iac and this keeps happening to me too

Schurkey

Have you connected a scan tool to see if the computer can control the IAC? Have you verified ALL the other sensors and computer outputs?

A perfectly-functional IAC will not control the idle if the wire harness is damaged, or if the ECM has corrupted programming or failed quad-drivers. Or, for that matter, if the computer thinks it's -40 degrees out because the coolant temp sensor--or it's wire harness--has failed.