I have a question about the IAC motor, I have been reading posts about people having problems with their car wether it be runs rough cold but good warm OR runs rough warm but good cold. In almost every post there is someone who says maybe its the IAC. Well I have a problem with mine not running good cold but it runs exellent warm, and before I go out and buy a $50 IAC can the IAC effect JUST cold or JUST warm? I know there are some very smart people on here that can answer this. Thanks for the help.

 

Anybody???? I really need to know. I have searched and searched and read books and it doesnt specify or what not.

 

Vader's article on Tps and Iac adjustment:



Yes, the engine should idle at the specified RPM for minimum air position adjustment (in DRIVE with an automatic).

I'm not sure what article you may have read, but try this procedure:

Throttle Minimum Air Position

Tools needed:
1. Torx driver # T-20
2. Paper Clip
3. Small Punch
4. Tachometer

GENERAL NOTE: The engine should be at normal operating temperature before performing any adjustments. Never rely on the dash mounted instruments for diagnostics and adjustments. The oil pressure and temperature gauges and the voltmeter and tachometer just aren't calibrated accurately enough for diagnosis, but are a relative indication for monitoring the vehicle while driving.

For this adjustment, the transmission will be in DRIVE while you're under the hood. You will need to securely set the parking brake and block the drive wheels. It would also be a good idea to have an assistant hold the service brake while you perform the adjustments.

In order to successfully complete the adjustment, the IAC air passages and pintle need to be clean. The throttle plates and bores need to be clean as well. If this is not the case, you'll need to remove the air cleaner from TBI engines or the intake air bellows from TPI engines to gain access to the area to be cleaned. A spray-type carburetor cleaner works well for this. Cleaning the IAC passages on a TPI/MAF engine will set a DTC, but we'll be clearing that later. With the engine idling, direct the spray cleaner in to the IAC air passages and around the throttle plates. Shut off the engine and continue cleaning the throttle plates by opening the throttle manually. Once everything is satisfactorily cleaned, replace the air bellows on TPI engines. Many times, this alone can solve IAC/idle speed problems.

If this doesn't solve the problem, you may need to remove and clean the IAC stepper motor. If the IAC appears to be clean and functioning properly, continue with the adjustment procedure.

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Idle Air Control Cleaning

You can remove the IAC and service it. Remove the electrical connector from the IAC. Unscrew the IAC unit from the throttle body.

You can gently rock the pintle back and forth and allow the spring to extend it until it comes apart in your hands. Clean everything with lint-free cloths and a mild solvent. Harsh solvents can affect the insulation of the stepper motor coils. It's generally the dirt and buildup on this worm shaft that causes sluggish IAC operation.

When the worm gear on the pintle shaft is clean and dry, apply one drop of clean light oil to the shaft and work the pintle back into the rack gears of the motor by the same rocking motion. It takes a while to get the pintle back into the worm gears, but you'll get it. It is important to get the pintle fully retracted into the housing so that the pintle is not forced against the gears when reinstalling the IAC unit in the throttle body.

While the IAC is out, clean the air passages in the throttle body. The orifice in the TB where the IAC resides is the seat that the IAC valve closes against, and it can accumulate a lot of carbon, dirt, and debris. The easy way to do this is with carburetor cleaner and a small stiff brush.

When everything is clean and dry, replace the gasket if it is damaged, apply a little anti-seize to the threads, and torque the IAC to the proper specs. (13 ft/lb for '85-'89 , 30 in/lb for 1990-on.) Proceed with setting the TPS and minimum air position.

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Locate the ALDL connector under your dash panel, in the driver's footwell area. Remove the plastic trim cover (if it is still there).

http://216.121.161.76/files/ALDLPlug.jpg

Cut and form a paper clip into a "U" shape. Insert the clip ends into the ALDL in the 'A' and 'B' sockets.

http://216.121.161.76/files/ALDL.gif

Turn on the ignition, but don't start the engine. This will force the ECM into its diagnostic mode. Wait 30 seconds to allow the IAC pintle to fully extend. Under the hood, remove the electrical connector from the IAC, then turn off the ignition and remove the paper clip jumper from the ALDL. With the IAC pintle fully extended (closed) all idle air will be controlled by the position of the throttle plates. Some manuals indicate that the EST bypass connector should be disconnected for this procedure, while some make no mention of it. While timing is a factor in idle speed, the EST should only operate as a function of engine RPM, temperature, and detonation sensor inputs. To remove all doubt, disconnect the EST bypass connector is your car is so equipped. Some TBI and V-6 engines do not have this bypass connector, and therefore must be set with no regard to the EST system. The EST can be bypassed on some cars by grounding the diagnostic terminal at the ALDL and continuing with the procedure, but the fuel mixture will be skewed to the rich side, affecting idle speed as well. In any event, the minimum air position idle speed range is wide enough to allow for some variations. As always, it is best to consult your service manual for the exact procedure for your system.

Locate the Torx screw on the left side of the throttle body. It may be equipped with a protective metal cap from the factory. This was intended to discourage adjustment. If the cap is present, use a small punch to knock it out. Once the screw is accessible, start the engine and place the transmission in DRIVE. Adjust the throttle stop to obtain 400 RPM with the transmission in "DRIVE" on an automatic transmission car, 450 in neutral on a manual transmission car, rotating the Torx screw clockwise to raise speed and counter-clockwise to lower speed. Once the idle RPM is set, place the transmission in PARK and turn off the engine.

Re-connect the electrical connector onto the IAC. Start engine. Idle speed should be governed by the ECM at approximately 600-650 rpm in "DRIVE" (for unmodified cars). Idle speed in NEUTRAL or PARK is less significant, and will be higher.

http://216.121.161.76/files/TBTPI.jpg

Throttle Position Sensor (TPS)

Tools needed:
1. Digital Volt-Ohm-Meter (VOM)
2. Breakout jumper wires or probes (make your own)
3. AutoXray, Diacom, or similar scanner will replace the VOM and jumper wires.

Turn on ignition, but don't start the engine.

With a diagnostic scanner: plug in the scanner and read the TPS voltage. It should be 0.54Volts +/- 0.07 VDC.

Connect the VOM to the TPS electrical connector terminals ‘A' and ‘B'.

With a breakout jumper: Disconnect the electrical connector from the TPS. Install the breakout in-line, between the TPS and wiring harness connector. Connect the meter probes to terminals 'A' and 'B' on the connector. (‘B' is the positive connection, ‘A' the signal ground, or negative.)

With probes: If you have very slender probes on your VOM, you can back-probe the TPS connector while it is attached to the TPS. If you have made probes of large dressmakers pins or a similar item, you can back-probe the connector as well. Connect the meter probes to terminals 'A' and 'B' on the connector.

Turn on the ignition to read the TPS output voltage at the idle position. The reading should be 0.54VDC +/- 0.07VDC. The ideal is the center of the range, 0.54VDC for a stock engine. To adjust the output voltage, loosen the two Torx screws holding the TPS to the throttle body, and slightly rotate the TPS up or down, reading the voltage until it comes into specification. Tighten screws. Using the throttle lever, rotate the throttle to WOT (wide open throttle). The TPS voltage should be over 4.0 volts. Close the throttle again, and then slowly open it to WOT, observing the voltage reading. It should increase progressively and in a linear fashion. If it sticks or jumps or falls off at all while doing this check, the TPS sensor may be failing and could be a cause of stumbling and driveability problems.

After achieving the desired setting, turn off the ignition switch. Remove all jumpers or the scanner and reconnect the TPS connector as required.

Reinitializing the ECM

If you set a DTC during the procedure, the SES light should be illuminated on the dash. This ECM retains DTC data for the previous 50 engine starts, so the codes will eventually be cleared. If you want more immediate results, after shutting down the engine disconnect the negative battery terminal for five minutes. This will clear the ECM of all diagnostic trouble codes. Clearing the ECM also clears any data learned about your engine, and clears the radio presets. If you have a Delco-Loc or Theft Loc II radio, make sure you follow the procedure to unlock the radio protection before disconnecting the battery. This five minutes is also just about long enough to clean both battery cables. Reconnect the battery. When you first start the engine after clearing the ECM, the engine will operate with base parameters programmed into the ECM PROM. These parameters may not be optimum for your engine, but the ECM will enter a Block Learn Mode soon after the engine is warm and enters Closed Loop Mode. The ECM will write new data tables specific to your engine and will eventually rely on those tables instead of the base tables of the factory program. You can expedite this process by driving the car for 20 minutes under varying conditions to allow the ECM to initialize. Or you can wait and drive the car normally at your convenience. The BLM tables are constantly being updated as sensor input ranges change, but the greatest change will occur within the first twenty minutes of Closed Loop operation.

 

I'm having very similar problems. When the car is cold it sometimes starts fine, other times it needs me to feather the pedal for 5 or so minutes until it idles on it's own. After that the idle hunts from 500-725 constantly....after about 10 minutes it idles normally.. I was thinking perhaps my eecs canister is purging when the car is cold, but I have also though about the IAC and the IAT sensors, does my car 89 5.7l have the inatake air temp sensor? If so, can this be a possible cause for my starting distress and sloppy throttle response, all other maintenance done, plugs, wires, etc... going to test TPS...car has 98k on it....also going to try to clean out IAC passages and sensor itself...sorry this was long...but this is really bugging me because once the car is warm it runs like a champ

 

Same thing here except on my first start 90% of the time it will not run for the first few min. unless I give it gas. I have done all the things that Vader has said in the above post, it helped a little.
My only real question for this post is can the IAC cause a problem for JUST cold or JUST warm? At this time I cant afford $50 which seems to be the going price for these. Can it be a vacuum leak? I have already found about 5, one being the EGR valve that was a PITA to figure out.

 

Yeah, that's the kinds of things I am afraid are in my future. I didn;t mean to make it sound like the car started, like yours it wont run on its own usually. Can it be the evap canister? I cant wait to get this thing figured out.......

 

The IAC does not do anything unless the ecm tells it to move.

I would look at fuel first, since that is a much more common problem. Depending on what temperature the CTS is reading, the ecm adds more fuel. The colder it reads, the more fuel added. If the CTS isn't connected, or is bad, then thats something you need to look at.

Hook up a scan tool or laptop via the ALDL port, and see what the CTS is reading. If you don't have access to a scan tool or laptop, you can check the CTS with a voltmeter.

Keep in mind that both of you guys have cars with a cold start injector that is at the very least 17 years old.

 

I just ran to the store and picked up some carb + throttle body cleaner. First I tested the fule pressure, all was within spec. Then I attempted to start the car....ran like ****. Moved it to the driveway and shut it off. Removed snorkle and MAF and began to lightly spray the intake and IAC passages. Then I started the car and resumed light spray. Shut of car once it was clear, opened butterflies and cleaned out the inside and backs of them , started the car with the maf off and it ran great with immediate throttle response and great idle, this was as I was spraying. Shut off car, reattached everything, and it still runs fine. I'm wondering if it's because of the maf or the spray....I'll let it sit until 8 tonight and start it again...keep yer fingers crossed.

 

I can tell U from personal experiance that if the throttle body is all full of crap, that it WILL NOT RUN RIGHT!

Basically (as it was explained to me) is the intake is cheating and taking in (or not taking in air) and not letting the ECM know exactly what is going on.

Hope that fixes it--let us know--we all learn from everybodies else's experiances!

C

 

ARGH.....so I'm on the board about to reply to this thread when all of a sudden I lose control of my pc. I cant click anything and it just keeps rebooting.....stupid exploit, I'll have to fix that now too....so on to the famiy pc I go. I'll write back tonight and let you all know if the car started...thanks for the replies!!!

 

well mine shines more on the inside then it does on the outside lol I cleaned that soooo good. I dont think that is my problem.

 

I'm still waiting until tonight to see if it works, that thing has to sit for several hours before it acts up. I still really wonder if disconnecting the MAF had anything to do with it...the previous owner had just replaced it....

 

Possibly.....but I think probably not.

The 2 times I haave had MAF problems on 2 different 89 IROC's, it would always start, but wouldn't run right or die when U gave it throttle.

 

Another question, Does the ECM use MAF readings in Open loop? If not then it cant be MAF related right? BTW I changed my CTS as well as the temp sensor located next to it (not sure what it is called i just changed it b/c as I was taking the CTS off i hit it and broke it) I also cleand the throttle body as well as the passages.
And replaced my MAF sensor $50, got it really cheap.

 

good luck

 

Did you check for vacuum leaks?

 

yeah....everything was cool

 

Ok...the car started then stalled, started then stalled, started then ran rough.....and I almost made a great commercial for the carb cleaner I used. Anyway...the problem to me at least seems to be a lack of air, the car will idle all on it's own, but as soon as I apply pressure to the gas pedal that's when the car really runs bad, as soon as I lift, idle resumes. It's a tough problem, but I think we can get it, in fact I really have no choice as this car is going to be my daily driver in about two weeks!!

 

I ran outside again, sheesh its hot, and disconnected the MAF....idle went up to about 1k and was stable, throttle response immediate, and of course I got the SES light. I shut the car off, reconnected the MAF and lo and behold the car did not run as well, but it also was not running poorly as it had been earlier, I wish I knew what this meant

 

My IROC has experienced the same type of cold running problems for a couple years. Like you guys, I was told "IAC" over and over.

I set my iac so many times that I comitted the process to memory. I've replaced the IAC twice, replaced the harness plug, replaced the ECM, burned new chips and done wire verification tests.

The car still has the same problems. The only thing I haven't changed is my throttle body. Currently I'm running a 100% like-new Holley 52mm. The only thing that I have left to try is to go back to a stock GM throttle body.

Hopefully some of you guys will find an issue/problem that I haven't already tended to so that some light can be shed on my problem.

 

I've read a few posts on TGO that people said they had nothing but problems with the Holley 52MM TB?

 

I really hope that my problem doesnt last for YEARS that would be horrible, and If I wanted to sell the car, I would have to warm it up for them lol that would be bad.

 

just cleaned the intake with some carb cleaner and it cleaned the idle right up on the 2.8 that has been jumping from 500 to 700 rpm and sometimes going so low it wanted to die... A good cleaning of the intake and the boot for the air cleaner and it stopped doing that almost immediately.

 

I've read that too, and maybe that's the case (I'll find out when I swap to a stock throttle body), but honestly, it would surprise me. The machine work on the holley throttle body is phenominal, and the IAC air path isn't exactly rocket science. All it consists of is a hole from the front of the TB to the bottom, then another hole from the bottom to the back.

 

Few words of thought here.

Flaking out sensors can cause issues in open and closed loop, MAF sensors included.

Most of the people here with problems seem to be having "iac"ish related issues.

All the v8 guys replying are also 85-88 owners.

U also have the dumb 9th injector for cold starts, and the associated leaks, bi metallic strip for the switch and the other garbage with it. No one has mentioned bothering to check any of this out or following the procedure for hard starts in the manual.

Might help a few of you find your problems this way. It will run real bad when it doesnt have enough fuel when its cold too :-)

U using your foot to keep it running a few times gets it wet enought to eventually run on its own.

Try verifying all your sensors like coolant and IAT and see if they are the same when cold and test them when hot also and see if the numbers jive(will both be different when hot obviously)

Not the Haynes, but some of the TPI swappers books ahve alot of this inof in them so if u dont have one, find one or somebody that does.

later
Jeremy

 

sounds like some good advice, I will have to get started checking some of that stuff. To me it seems like it's probably just some little niggling thing that has to be found, but it's well hidden! If I find anything I'll let you know!!

 

I have been hearing about this 9th injector and cant even see it on my car, where is it? Is there a way to test if it is leaking or a way to test if it is working? Now that you mention the symptoms it would make sense to look at that.

 

The cold start vavle or the 9th injector is located under the plenum between the rear 2 injectors on the left side (drivers) of engine. There is also a sensor in the front of the intake for this valve. It has a connector much like an injector and is located next to the CTS under the throttle body. Under 100 degrees this sensors allows the cold start valve to run for 8 seconds to help the engine run. The valve or the sensor may be bad in your case.

 

My cold start injector has long since been removed and I've been running various 89 TPI PROM codes. All MAF related equipment has been replaced at one time or another since I started having the idle issues.

 

damnit I was afraid of that I just took off my Plenum about a month ago and didnt even think that it could be a problem at the time. Is there a way of testing it with out taking off the plenum again? If not looks like I will be needing some gaskets huh.