87tunedport

thanks for the info ill get that replaced today

87tunedport

i appreciate all the info. never would have gotten this far with out you guys help. this has been the most helpful forum i have been on so far

87tunedport

ok lets say it is the CTS causing the car to idle low. would the car idle crappy all the time? cause the car has a nice idle when engine is cold but once warmed up is when it idles poorly. i could be wrong im just asking. i am by no means a technician

lonestar7

iTrader: (1)

A quick question for the experts, is the CTS used for the temp gauge also or is there yet another sensor for that?

87tunedport

see post 38-40
if you are referring to the one i am replacing in the intake manifold, no that one is for ECM the one for the temp gauge is located in the driver side head near the front. at least on my v8 tuned port engine it is

87tunedport

ok i got one on order gonna be here tomorrow. lol seems like i wait on ordered parts more then i drive and enjoy the car

87tunedport

got the part in, car has no more smoke and alot less gas smell so that was good news. idle had no change though.

ASE doc

Ohm your injectors?

87tunedport

yep all were between 16-17 of each other hot and cold

ASE doc

I just read through the thread to refresh my memory as to what you've done. I don't know, from what I've read, if you've actually performed the factory minimum idle air adjustment procedure. In this procedure, you force the IAC to close by placing the system in diagnostic mode. This is the same mode you read codes in where you jump terminals A & B of the ALDL, then turn the key on. Wait 45 seconds for the IAC valve to seat fully, then without turning the key off, unplug the IAC. Now start the engine and set idle speed to 450rpm. Then set TPS to .54 volts +/- .4 volts. Once finished, turn the key off, reconnect the IAC and remove the jumper from the ALDL.

If after doing this, exactly as written, the engine still idles low, you need to find a scan tool and look at fuel trims to see if the system is going lean or rich when warm and causing the low idle. With the scan tool you can also view commanded idle and IAC steps. By turning on the AC, you can force the ECM to command the IAC to open. I don't remember right now if more steps is more open or visa versa but you'll figure that out by playing with it.

Using a volt meter or test light, you can watch the ECM try to activate the IAC coils to open or close to valve. The 4 wires to the valve are coil A and coil B driver circuits. The ECM applies power to one side of the coil and ground to the other and switches from coil to coil to move the pintle. With the IAC disconnected, you can use a test light at the connector to see this. Or you can use a DVOM either at the unplugged connector or backprobing at the IAC. Pins A & B are coil A and pins C & D are coil B.

One quick test of the IAC and control circuit is to monitor idle speed on engine start up. When started, the engine should idle up to 1,200 to 1,500 rpm and slowly come down to idle speed. When fully cold, the engine may go as high as 2,000 as it goes through after start enrichment decay. If this isn't happening, you either have IACV or IAC control circuit issues. The voltmeter test can point this out but a lab scope is better for actually seeing the on time/off time.

There is an IAC tester made by Thexton tools that makes quick work of testing the valve itself. Once you know the valve is good(since yours is new,it's probably okay) you can move on to checking the control circuit and IAC drivers.

87tunedport

ok ill try to redo the minimum idle procedure. the only thing i have done for minimum idle was turn stop screw till it no longer touched the throttle, then connected my volt meter to TPS and turned the stop screw until i got .1 volt more on the TPS read out. ill give this a shot and report back. can i use the tach in the car to read RPMS? i heard a bunch of people say that is not precise enough to set idles

Tuned Performance

iTrader: (92)

Im not sure who told you how to set the minimum idle speed that way but there wrong. I asked you on post #6 if you covered this and ou said you did. Sounds like its jacked up worse listen to Doc

87tunedport

alright i believe i got the minimum idle set but still have the low idle. if i had a problem with valve seals or piston rings could that lead to a bad idle? im not saying i know i have internal problems, but its a v8 trans am i know it was used and abused (thats what makes me mad about buying used, i buy someone elses problems). with everything set correctly im thinking its not electrical related. im gonna go test the fuel pressure now. i dont think i tested it before. im coming to my whits end on this problem lol

87tunedport

i was reading another thread on idles and a member chimed in with that method and said it worked great for them. i thought minimum idle was set right and i was having problems with my TPS but i dont think thats the case anymore

87tunedport

hey does this help? i went to put gas in the car once i loosened the gas cap i heard a hissing sound coming from the cap like pressure was there and when i loosened it pressure escaped. i have never head a vehicle that
did that from the gas cap before

ASE doc

It is normal to have some pressure or vacuum in the tank, depending on temperature. As fuel warms up it expands, as it cools it contracts. The fuel system is sealed to prevent vapor release into the atmosphere. It normally vents only through the charcoal canister.

87tunedport

ok well that good to know nothing is wrong with my tank. im pretty sure i got the minimum idle in the ball park range by doing exactly what you said and TPS is set to .54 cause the engine does run to 1500 like you said and slowly comes down (this is warmed up) but it keeps going down its at like 500 im park when i put it in drive it goes to 200 and sounds very poor and shakes. my ac is gone but still have the switch in my HVAC controls can i still force ECM to command IAC? do you know what the voltages thECM sends to IAC to activate coils? im on my way out to pick up a fuel pressure test to test the system

87tunedport

i just hooked my multimeter to the A-B of my IAC by back probing them, had a buddy flip the key to on and i got a 9.98 on the meter she turned it off, then i got 10.28 before going back to 0.00 im just trying to see if the ECM is activating idle air control valve the right way

ASE doc

The ECM activates the IAC coils with 12 volts. The control pattern is an on/off square wave signal. If you had a lab scope and could watch the pattern on both coils simultaneously, you would see one coil turned on and off then the other turned on and off. I have seen bad drivers in the ECM before and the control pattern turns into garbage. The control voltage may appear lower than 12 volts with the key on engine off due to the alternator not running.

87tunedport

where is the ECM located?

Tuned Performance

iTrader: (92)

Under the dash next to the kick panel on the passenger side.

87tunedport

ok if drivers in ecm are bad can they be repaired or do i need to replace the ecm?

ASE doc

Most anything can be repaired but I generally just swap in a remanufactured ECM. They're relatively cheap. I'm curious though since your engine does idle up after started. I would really like to see what the ECM is doing through data stream. The IAC steps and idle speed should respond to changes in engine load. One behavior to look for is a delay in the engine returning to idle after opening the throttle. This is to prevent stalling during decel fuel cutoff. Try duplicating this by raising engine speed to 2,500 rpm for several seconds then releasing the throttle. If the idle stays high for a moment before dropping, that tells me that the IAC and IAC controls are working. There may be another issue affecting idle speed. If the IAC or circuits are faulty, the engine will drop back to low idle immediately.

It's possible that the IAC drivers are heating up and dropping out, but that would be more inconsistent and would most likely be worse in hot weather.

EDIT: I just reread post #67 and obviously, if the IAC and controls were responding to engine load, the idle wouldn't drop to 200 rpm and stay there. In fact, the ECM should very quickly open the IACV and the idle should spring up a little when the engine is placed in gear, then the idle should settle back down to 550.

87tunedport

is there anything else you would recommend checking out? i would love to see what the ECM is seeing and how its adjusting the idle, but yesterday i had to renew my insurance and plates which socked me pretty hard. at the moment i would be lucky to have a penny in my name lol, you mentioned a tester by Thexton to test the IAC ill have to see what next pay brings. is there anything i can do with my multimeter?

i did try testing fuel pressure but idk if i got a bad gauge or i actually had 0 pressure but gauge would not register anything (not even a flick) with key on or engine running. i turned the car on and off like 7 times to see if it would build pressure and got 0 damn loan-a-tool Autozone
if i did have 0 pressure the car would not run at all right?

Aero

I have a similar problem, and I am currently under the process of seeing if changing the head gaskets/other gaskets would help.
If you have a leak in any of your piston areas, it can lead to a choppy/low idle.
Try doing a compression test. For me cylinders 3/5 had a leak, so right now I am going into my car and trying to change my head gaskets as well as the others since im down there. I am not that much of a mechanic myself, but it is a learning experience, and hopefully I am not messing up.
But that's just my two cents. Try doing a compression test and see if you have a leak somewhere.

ASE doc

Zero fuel pressure= the car wouldn't run at all. More likely, the valve core depressor that is supposed to be in the adapter of the gauge was missing. They drop out if the user isn't careful. It probably ended up under the car of the last person to use the gauge. Is there no response at all in idle speed to shifting into gear? Besides just dropping to 200rpm? Does the idle rise at all for even just a moment.

Aero brings up a good point about compression and engine health, but you would still get some response from the IAC. The ECM monitors engine rpm and tries, by moving the IACV, to maintain programmed idle speed. Of course 550 rpm is low and if the engine has low compression on a few cylinders or otherwise can't support load at 550rpm, you will get a very rough idle. Low idle, not so much.

The DVOM is limited for testing the IAC and circuits. You can test the coils of the valve and test for control voltage but if the voltage isn't what it should be, you will have a hard time seeing drop outs or glitches in the signal with a digital voltmeter. A test light is almost better for this test than a digital meter. You can watch the test light flash and see that is doesn't go dim or flicker. A logic probe like the Power Probe would be good but they tend to run $100+ and you could just get winALDL and make up a patch cable and get closer to what you need.

A general circuit test I learned in GM school years ago was to use a 12 volt bulb in place of the load. In other words, make up test leads connected to a light bulb and connect them to one side of the IAC valve connector at a time and see if the bulb flashes brightly and doesn't flicker when the load is activated. In this case the load is the IAC valve and you could activate it by tuning the key on or by idling the engine with the valve unplugged.

Different bulbs draw different current. A headlamp bulb draws around 5 amps while a brake lamp bulb draws about .6 amps. This places a load on the drivers and may point out a problem. But until I've tried a test like this on an IAC circuit myself to verify it works and doesn't damage anything, I can't recommend it.

The Thexton tool we have is pricey if you can even find one anymore. It just verifies that the valve is good or not. You still need to verify the circuits are okay then you can replace the ECM and know it will work. You could try PMing Tunedperformance and see if he has your ECM on the shelf. He might be willing to loan you one to try.

Tuned Performance

iTrader: (92)

Another way to make a inexpensive tester is to use a bipolar led with a 1k resister jumper each coil wire at the iac 4 pin connecter to check the ecm commanding iac movement. I do have a couple 165 ecms and I will loan you one but I had a issue with one I loaned out months ago and have never had the user purchase it or return it. So I would require you to purchase it for $50 but will refund you purchase minus the paypal fee and $12 for the initial shipping cost if that sounds fair.