IAC fried?

[Drewkimble48]

93 gmc c1500 tbi 350
So I dropped in a new distributor and the truck started idling unstable. Became frustrated and took my truck to a shop.
I knew my old distributor was old and tired and was creating some idling issues is why I had decided to get a new one. The thing though is that the plug that goes over the idle screw on the throttle body was taken out. So after taking it to the shop and getting it back, it Idles better.
Well curious of what it was, the guy that worked on it told me that the timing plug was unplugged which I knew it was unplugged because I unplugged it to set timing and it was the only way it would run to the shop . what he did was plug it back in and adjusted the idle screw. Yes it runs better but, I am a little worried that it was just patched basically by adjusting the idle screw up to make it run better you know what I mean?
Also I think while I was trying to fix it, I think the IAC was fried because I saw it smoking in the throttle body cavity.
I just want to see what you guys think of this and if you guys think my IAC is fried.
Sorry If this doesn't make sense, I'm just alittle frustrated and in a hurry to write this because I'm at work.

[Drewkimble48]

Quick update to verify my theory. adjusting the idle up did not fix it because I just started it after letting it sit to cool down and it's still doing it. So I'm royally pissed off at the place for doing what they did. So called "Genius". BullS@#%!
I have no way of knowing what the timing and base idle is at unless I spend big money on a timing light with the rpms displayed on it.

I know this much, compression checks out good, vacuum good and fuel pressure good.

[eagleuh1]

If you have a laptop you can download a free program called winalde, then buy a usb cable to connect your laptop to your ALDL diagnostic port on the truck. You can then see what all your sensors are reading. And it will tell you any codes your ecm is throwing as well. Do you have a check engine light showing? The smoke you saw was probably just fuel vapors coming back up through the passage for your IAC . Mine does it every time I shutoff the engine.

[eagleuh1]

If it ran good when you got it back from the shop, why did you try and "fix" it?

[Drewkimble48]

Originally Posted by eagleuh1

If you have a laptop you can download a free program called winalde, then buy a usb cable to connect your laptop to your ALDL diagnostic port on the truck. You can then see what all your sensors are reading. And it will tell you any codes your ecm is throwing as well. Do you have a check engine light showing? The smoke you saw was probably just fuel vapors coming back up through the passage for your IAC . Mine does it every time I shutoff the engine.

Yeah I've been thinking about doing that for a while but, the laptop runs pretty slow. I might see if I can use my dads possibly. Is it compatible with Apple?

Originally Posted by eagleuh1

If it ran good when you got it back from the shop, why did you try and "fix" it?

They adjusted the idle screw up. I haven't even touched anything since I got the truck back. Its frustrating to pay $100 to a shop that did not fix it.

[eagleuh1]

Winalde works on older laptops better I think than newer laptops. It's been around for a while. Look up Hamilton ful injection on Binder planet. He sells a cable that connects to truck and laptop for $32 I think I paid. Works good. I had to trim the connectors a little to make it slide in easier, but works good. He also has troubleshooting forum. Lots of info. Jim

[eagleuh1]

Look here
http://www.binderplanet.com/forums/f...aysprune=&f=75

[ChevyTech]

After the engine is turned off, vapors from the intake manifold came escape through the IAC passages.

Did you see a little vapor after you shut it off?

If it has an automatic transmission then WinALDL will not work on it.

The 4L06E is shifted by the computer and they changed to a much faster computer to do this. If it has a 4L60E WinALDL will not work.

A manual transmission 1993 truck still has the old style, 160 BAUD, slow ECM.

WinALDL is a 160 BAUD reader. WinALDL will not read a 8192 Baud data stream.

Tuner-pro can read a 8192 Baud data stream.

[Drewkimble48]

Well I know this much now. I can go through the procedure to reset the IAC only for it not to start immediately unless you unplug IAC or give it some gas with it plugged in. After that though it starts hunting basically. Idles up and down. If you disconnect the IAC to do the reset procedure, truck idles great. So it's all tied into the IAC somehow. Vacuum is at 20" in park and 19" in drive with miniscul fluctuations. No fuel pressure flu cations either
Quick question though for you guys is now the screwed up the idle screw, I'm trying to figure out what it's suppose to idle at for a stock 93 gmc tbi 350?
Thank you guys for the help. It's been greatly appreciated.

[Drewkimble48]

Well I figured it out. Noticed how much my timing kept jumping. I went ahead and pulled the new distributor out and dropped in my old one with the new cap and rotor the new distributor came with. Times it and it runs perfect but now I can't get the engine to kick up when the A/c is on. It goes right back to where the engine normally idles at when the a/c is off. Any thoughts of what it could be?

[speedygonzales]

It would appear your "idle" screw is what's determining your idle speed instead of the IAC which according to what you said earlier is fried anyway. So? What's so hard to figure out?

If the IAC is not being used to set your idle, how would it change the idle according to load like engaging the AC?

Get a working IAC and back the idle screw off and see what you got. Pretty simple by the way I see it.

Unless I read something wrong.

[Drewkimble48]

Originally Posted by speedygonzales

It would appear your "idle" screw is what's determining your idle speed instead of the IAC which according to what you said earlier is fried anyway. So? What's so hard to figure out?

If the IAC is not being used to set your idle, how would it change the idle according to load like engaging the AC?

Get a working IAC and back the idle screw off and see what you got. Pretty simple by the way I see it.

Unless I read something wrong.

yeah since those the shop touched my idle screw, I have had hell trying to get it to where it should be at. I've almost got it but, I'm just hitting a wall with the IAC valve. I can see the IAC operating when you blip the idle and when you put the truck in limp mode, it retracts itself leaving it where air can pass through it, making it harder to dial in the idle speed screw when the truck is idling in drive at 900 to 1000 rpms. I'm not really tech savy when it comes to using tuner pro or any of that. I rather just have someone scan it to see what everything is doing. the problem is I can't find anyone in the dfw area that has the capability to do that.

[speedygonzales]

SMH

Back off the screw so it's using the IAC

[Drewkimble48]

Well, I have set my throttle back down to where it should be via the tps sensor at .54 volts to be exact. I have also went ahead and bought tunerpro and a aldl cable to see what the engine is doing. all seems well now including the iac counts and it now idles up when the a/c is engaged so now that seems to be completely solved. Now the only problem I run into is the intermittent engine miss when the engine is warmed up and at idle. I can see when the engine miss happens on tunerpro and found out that every time is misses, the ignition timing is retarded significantly which leads me to believe that I am now dealing with a ignition related issue now.
As far as what has been replaced ignition wise I have replaced:
Spark plugs: regular AC Delco gapped stock .35
Ac Delco plug wires
Accel distributor cap and rotor
Wells/Carquest ignition module w/ grease on bottom.
And this is using the old distributor still just to throw that out there.
knock retard is around 23-24 if that helps to understand.
I am able to get more engine data if need be to.

[ChevyTech]

Many TBI trucks get a strange rhythmic misfire or stumble at idle when the fuel has ethanol in it. The higher the ethanol content, the more noticeable it is.

I you have poured anything in the gas tank, wait until you have a fresh tank of fuel before you get to involved in the idle misfire.

If the system is retarding the timing just before the misfire happens, I would watch the knock counts and see if there is a considerable increase just before it retards the timing. If so, I can go into detail on the possible causes.

If the timing retards happens just as, or just after the misfire, I would say the misfire caused it.

[Drewkimble48]

Originally Posted by ChevyTech

Many TBI trucks get a strange rhythmic misfire or stumble at idle when the fuel has ethanol in it. The higher the ethanol content, the more noticeable it is.

I you have poured anything in the gas tank, wait until you have a fresh tank of fuel before you get to involved in the idle misfire.

If the system is retarding the timing just before the misfire happens, I would watch the knock counts and see if there is a considerable increase just before it retards the timing. If so, I can go into detail on the possible causes.

If the timing retards happens just as, or just after the misfire, I would say the misfire caused it.

I was actually looking at the knock counts last night when my timing would retard and did not see any change to it when the misfire would happen.
As far as when the timing retards, you can see that it is retarding prior to anything. once it does, you can see the MAP increase after the peak of the spark retard along with the IAC. regardless of the phases the 02 sensor would be at, the retard would happen when it it was rich or lean. Knock retard would take a small dip when the timing retard but nothing substantial.

[Drewkimble48]

Oh also the average rpm the truck idles at in drive is about 525 rpms. At the peak of the ignition retard, I have seen it drop down to 475.

The blue line in the picture that follows is the 02 sensor
green, spark advance
MAP: teal
Red: engine rpm

[ChevyTech]

Oh also the average rpm the truck idles at in drive is about 525 rpms. At the peak of the ignition retard, I have seen it drop down to 475.

As the RPM drops, does the IAC count remain constant, go up, or drop the go back to where it was?

Does this vehicle have headers on it?

Does it have a one wire oxygen sensor?

Have you watched the open/closed loop status to see if it is switching from closed loop to open loop as this happens?

It looks like the oxygen sensor is cooling off as it idles to the point it is not longer giving a good voltage reading.

[Drewkimble48]

The Iac will go up once the timing has retarded. It doesn't go up exactly with the timing but soon after the peak it will increase IAC count
NO headers, stock exhaust manifolds.
It is a one wire o2 sensor.
When I drive the vehicle before it warms up it will be in open loop but soon after will go into close loop. if its not up to temp it will go back into open loop sometimes. I will have to look at open and close loop alittle closer when i get back to my computer. I'm at work right now and will be off soon.
I have been wanting to upgrade to a heated 02 but, would prefer not to tap into a wire for power and risk that connection breaking look to a vital component for operation. I'm not at the best as far as wiring goes haha

[ChevyTech]

A heated oxygen sensor is better but if everything is stock you can get by with a one wire sensor.

It depends on how often the occasional misfire is, how noticeable it is, and how much it bothers you.

You may want to try different fuel.

You may want to clean the carbon deposits from the engine and see how much that helps. If the engine has been run with a defective or to cold of thermostat, I would strongly suggest carbon treatment twice.

[Drewkimble48]

Well as far as depleting the carbon deposits, I have run seafoam the times I have ran to amarillo (362 miles) one way on a full tank of gas. As far as the ignition misfire, it happens more often when the engine is at temp idling. The gas mileage is great on the truck (around 18-22mpg).

[ChevyTech]

If you are getting that kind of gas mileage then it is running pretty well.

Here is what I have wrote in other threads about SeaFoam:

Carbon deposits can be very hard to get rid of. I have had the best success using the added thru carburetor instructions on the can.

I slowly pour in a half can in the HOT engine at fast idle then stall the engine and let it sit ten minutes. Then I slowly pour in the rest of the can at a fast idle, and then go drive it.

I have used SEA FOAM several times with great success. I have also used GMs TOP ENGINE CLEANER at the dealership many times with good results. The GM Top Engine Cleaner smells just like SEA FOAM to me and I have wondered if they are the exact same product. I have never had any problems from using these products, but if an engine has very heavy carbon, one treatment may not get it all out. My biggest concern is that it is not poured in so fast that it liquid locks the engine.

[Drewkimble48]

Yeah I love seafoam. I've put some into my oil once before and I think it helped alittle bit. I was hesitant doing it since it's a non-viscosity liquid but everything still seems alright.
Besides that, tonight I thought I go ahead and crack open the throttle just alittle to see if it would help the idle. It's not as bad as it was before but the real test to know if it helped is when hot days come back around and I have the A/C on in stop and go traffic. That's when it really starts to idle like dog poo. I'll probably check tunerpro again to see where the IAC counts are at since I touched the idle screw again.
Does anyone have suggestions as to where I should put my 12 volt power wire for when I get a 3 wire o2 sensor? I think I ought to at least upgrade that and see if it improves more