Gary Berg

Hi im trying to adjust my Idle Air Control and My Throttle Position swith on my 91 t/a 305 tpi. not sure of there locations? I have all the tools needed to adjust both. but i cant seem to find the ALDL, IAC or the TPS.

Vader

First, there is NOT ANY adjustment of the IAC. It is completely under the control of the ECM and nothing you can do to it short of damage can "adjust" it in any way. The phrase "IAC Adjustment" has been misused for just about 20-some years now, and is a complete misnomer.

The only things you can do to affect the idle RPM and how the IAC reacts is to either reprogram the ECM or to adjust the minimum air position of the throttle plates. Reprogramming is seldom necessary unless there is some mismatched cam installed. Checking (and if necessary, setting) the throttle minimum air position is supposed to be part of a tune up, and should be done as normal service. This has nothing directly to do with the IAC. The IAC merely adjusts the bypass air based upon what the ECM reads as RPM and programming.

Gary Berg

i love this site!!!! thanks man!!

Gary Berg

does the car need to be warmed up before i adjust the IAC?

Vader

Perhaps this will help:

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 brakes 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 into 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. Measure the free length of the spring, and stretch it carefully if necessary to make the free length at least 2¼". Assemble the parts in proper order, start the pintle shaft into the stepper motor in the correct orientation (paying attention to the keyways), 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 oriface 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 Assembly Line Diagnostic Link connector under your dash panel. Remove the cover if it is still there.




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




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. With the ignition still on, go 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 400-450 RPM with the transmission in "DRIVE" on an automatic transmission car, 450-550 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.



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.

Reid Fleming

iTrader: (2)

I'm assuming you mean before adjusting the min idle speed screw. The answer would be yes.

If you try starting the car with the IAC unplugged (after you've done the paper clip/30 second wait/unplug IAC/shut off the car routine), you'll find that your car will idle somewhere around 300 RPM or so. It'll start but it won't stay running unless you keep your foot on the gas. Basically the car is in cold rich mode but since the IAC is closed and not connected, the car is running on restricted air.

With the car warmed up, it will idle easier and should make the min idle speed screw adjustment much easier to do.

I need to do this in the next few days myself. My car will idle at 1000 RPM during a cold start, but will idle too low at red lights when it's warmed up. The alternator seems to not run too well once the car gets below 700 RPM. (I have a digital volt gauge that plugs into the cig lighter)

Mine currently idles around 500-600 RPM at full operating temperature. Traffic jams will send my voltage too low. Shifting into neutral will bring the RPM up enough to let the alternator work. I'm going to adjust mine so that it maintains 700-750 RPM at full operating temp in DRIVE.

If you haven't cleaned out the throttle body yet, you'll notice an amazing difference after you do.

Gary Berg

I cleaned it and i noticed some diff. but when i cleaned the iac motor i noticed less hesitation.

Reid Fleming

iTrader: (2)

You're right. I meant to say TB and IAC. I remember when I cleaned mine, the throttle body looked clean to the eye. But after seeing all the black gunk come out, I was absolutely amazed.

88PontiacT/A

OK, I know this is old, but I need to know if the ALDL diagram shown here (by VADER) also works for 1988. I have seen some that say that A= #6 and B= #5, and some that say otherwise (like A= #6 and B= #12 or something like that)
Thanks,
John C.

LUCKY 1

hi Thanks rjtc for turning me here. NOT SURE MECHANICAL ENOUGH TO DO ALL THIS BUT ATLEAST I KNOW I DO HAVE SOME OF THIS PROBLEM MINE RUNNING WHEN OPERATING TEMP 1,000 RPMS LUCKY 1

megan.artiaco

Very informative thread here!

DJK90IrocZ

Vader...

I wanted to ask you....Would I need to adjust my engine timing first before doing the IAC and TPS adjustments or the other way around?

I just recently had to replace my intake manifold gaskets, since they had been leaking oil on top of the manifold too much. I guess thats what happens to 21 year old cars.

Thanks for all of your help!!!

Rickey_85TA

.

Benc1

iTrader: (10)

So I have been trying to accomplish this but no luck. With the iac pintle fully extended and then disconnected. I can restart the car but can never get the idle down to 450 to 500 rpm. If I get any lower than 700 the car cuts off. I just can't figure it out unless it's the air foil that is installed on the throttle body causing problems. The car also has Bosch III 19lb injectors, under drive pulleys and bbk adjustable fuel pressure regulator (pressure set at around 48). I've set it as low as possible and reconnected the iac now the car is idling at around 1000 to 1300rpm which is why I started this process in the first place. I've also tried cleaning the throttle body before I started messing with the iac. I never went any further because I feel like I am doing something wrong. Any ideas

neilcase

HELP! I have an 87 305 TPI/5 speed car. It sat under a redwood tree for the last 10 years. I bought is as a parts car for my 87 convertible but decided save it because the whole original car was intact. I have spent two months reviving this thing from dead. It runs pretty good now except for one thing. I CANT GET THE IDLE SET! I've done the exact procedure outlined in this thread 3 times now and it sets OK for about 3 minutes and then it slowly works its way up to 1500 and settles there. If I cant get this solved I can't get it smogged and then it goes back to being a chopped up parts car and that would be a damn shame. Somebody help. Here's what I've done.

1. cleaned entire throttle body and intake
2. All new TB gaskets
3. New IAC control valve
4. virtually every sensor on the engine is new as well
5. set the timing to 6 degrees
6. followed the procedure here 3 times (idle stays at 550 with EST and IAC unplugged)
7. Checked as best I could for vac leaks
8. forgot to mention that the throttle screw is backed ALL THE WAY OUT AND CANT BE BACKED OUT ANY FURTHER TO CLOSE THE PLATES ANY MORE. So its gotta be an IAC a vac or an ECM issue?
9. (sorry another edit) I also set the TPS to exactly .54 volts
10. (edit) I just sprayed starting fluid all around the TB and plenum to see if there were any vac leaks. Nothing happened and I soaked it pretty good. (I know a lot of you will say that is stupidly dangerous). But that seems to debunk my theory of possible vac leaks. Comments about that? Is that a reliable way to test for vac leaks?

Here's what has NOT been changed

1. Mass air sensor (cant see why the car would run so good otherwise if bad MAF)
2. ECM (I'm beginning to suspect this is the problem)

I'm thinking either the ECM is buggered up or this thing is pulling air from somewhere at idle. But the fact that idle stays at 550 with EST and IAC unplugged leads me to believe it is NOT a vac leak problem? Its either a bad IAC (brand new) or a ECM program problem. Would there be any other symptoms of an ECM issue I could look for?

Ideas anyone?

85Special

Mine sat for 12 years 3 under a pine tree, wanted to kill my friend for that one than 9 in a storage unit. In that time my ECM went bad. Condensation probably dunno for sure but it was shot.

neilcase

OK the problem is gone but.... I got impatient and did two changes at once so I don't know which change solved the problem. I swapped the ECM from my 87 convertible into the 87 t-top car and then I went through the IAC and TPS setting procedure WITHOUT unplugging the EST when setting min idle. Runs perfectly now but as I said I don't know which change did the trick. I suspect it was the ECM and not the EST so in the near future I am going to swap the original ECM back in and see what happens. Stay Tuned. God that was a bad pun.

neilcase

I've read quite a few threads that say it is rare for an ECM to go bad. But it certainly looks like the case on mine too. I think for you and me the key is that it sat outside in the elements for so long. Granted, under a redwood tree in CA is not as harsh as in a barn in Minnesota but it seems to be enough to bugger up the ECM.

On a side note. Looks like I'm going to snag an 89 convertible with 305/5 speed (5 speeds on convertibles are rare) and dual exhaust for a really good price. I'll probably try to flip this car so if any of you know somebody who wants a bright red convertible in slightly above average shape let me know.

cuzimanoob

neilcase, did you happen to figure out what was the fix to your problem? I have an issue where my idle is low and really rough it keeps going so low it wants to die then it revs kinda high and keeps bouncing around then it finally dies, no matter in Park or Drive. I also hear a knocking at low rpm, but only when its having its stuttering problems. I changed the IAC but I dont think I adjusted it correctly, so thats on my todo list tomorrow. I'm going to have the timing checked and vacuum lines checked as well this weekend at a friends house who knows a lot more than me. Thanks for helping out a 3rd gen Noob.

neilcase

Noob,

I did eventually get it solved. I replaced the IAC valve and then I followed Vader's instruction to a tee found in this thread. it is very important that you do the steps EXACTLY as Vader says. In fact I had to do it more than once. But it finally worked. Note that I had to do it more than once because I was not patient with the results. Once you do the procedure there is a good chance that the engine won't run perfect until you drive it some. The ECM needs to re-learn many things in order for it to settle into a groove and run correctly. Mine runs absolutely perfectly now. Starts up within 2 seconds, idles great and does not stumble at any point in the throttle band.

tillyvick14

Hi, I'm having some idle issues on a 350 TPI Formula and unfortunately the min idle screw is completely stripped out and can't be adjusted on my car. Does anyone know if there is a new/replacement assembly that I can purchase somehow? Thanks very much for your help!

Tuned Performance

iTrader: (92)

https://www.summitracing.com/parts/sum-228714/
Summit has replacement Throttlebodys on sale.
This one has 89/92 linkage.
or you can place a ad in the wanted section or eBay for a used one.

Tuned Performance

iTrader: (92)

85-88 linkage
https://www.summitracing.com/parts/sum-228706/