Hello and thanks in advance for your suggestions. I apologize for taking up space being a newbie and if this topic was already covered, but I’ve been looking at the forum for some time before actually joining and highly value the member’s input. I purchased a 1987 IROC, automatic, 305 TPI in December, all original from what I can tell. My problem is that it will sometimes stall when I put the car in gear after the engine is warm. This occurred again today when maneuvering into my garage and going between drive and reverse. Otherwise the car runs and idles fine and the only time it has ever stalled is when putting it into gear. I just recently had a tune-up completed with new AC Delco plugs, wires, distributor cap, rotor, pcv valve, and air and fuel filters and still the same thing. The guy I purchased the car from was selling it for someone else and he said it basically sat in the garage for over a year because the owner worked out of state the majority of time. I have driven the car very little since I purchased it because of the winter weather here. My mechanic thinks the problem is likely being caused by the old leftover gas and also added a fuel additive, and said to run the tank low and then fill it with premium and that this will likely take care of the problem. Any comments or suggestions? Thanks again for your help.

 

Driving a tank of pr gas will help. Get it out, get it good and hot, do a few 1/2 - 3/4 throttle take off's, this will open the injectors and get the gunk to pass on through. It really helps.

 

Thanks for the reply. I'll do that when the weather clears up and let you know how I make out.

 

The problem is still continuing. I've since noticed that when it occurs my voltmeter is only showing around 11 volts. When I start the car or if I'm driving I show 13 volts, but after the engine warms and my rpms drop when idling, I sometimes only show 11-12 volts. Also my gauge drops down all the way to about 8 volts when my fans kick on before coming back up. Could this somehow be the underlying cause of my problem? The car still only stalls when I put it into gear after the engine is warm and otherwise runs and idles fine. I've also since learned that the seller replaced the alternator and ignition module in November. Thanks again for your help.

 

Check/set your base timing
Check/set your TPS
Check/set/clean your IAC

If you feel a bit more energetic you could have your ignition module checked out for free at most of the Autocrap zones.

 

Pull the alt and have it rechecked. Dropping to 8 volts is not good. Check at the Battery with a volt meter when the fans turn on, weak/bad connections will do this too.

 

Thanks guys, I'll get everything checked out. Also, when my engine warms up I'm only idling at about 600 rpms when the transmission is in park. Should my idle speed be higher? Thanks again for all your input.

 

Mine idles at 750 park and 550 drive.

 

Welcome Aboard!

There may be multiple problems, but the low idle RPM will affect the alternator output voltage as well as some of the other issues, so that would be among the first things to reconcile.

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.

Very little apparent varnish and dirt accumulation on the IAC pintle rack gear can cause poor or no operation. This is a comparison between a completely "dead" IAC and a completely funtional one, after cleaning:



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.



Check the spring free length. Stretch the spring as necessary to get a minimum 2¼" free length. When the worm gear on the pintle shaft is clean and dry, apply one drop of clean light oil to the shaft, align the keyways with the keys molded into the IAC body, 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 the dash panel, in the driver's foot well area. Remove the plastic trim 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. 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 if 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.



Throttle Position Sensor (TPS)

Tools needed:
1. Digital Volt-Ohm-Meter (VOM)
2. Breakout jumper wires or probes (make your own)
3. OPTION: 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.

 

Thanks everyone for all the information. I really appreciate it. Not sure if I'll attempt everything myself as I'm not the most mechanically inclined person, but now at the very least I'll be able to suggest some things to my regular mechanic and play a more active role in trying to diagnose the problem. Knowledge is power. Hopefully, I’ll have something to contribute to the forum as well someday.

 

none of this is really that technical, nor mechanically intense. If you follow the instructions closely, there is almost nothing which can go badly. The most critical steps are getting the IAC initially (since it could be seized after all these years) and being certain the IAC pintle is fully retracted before installing it. Application of penetrating oil a few days prior to removing it can be a huge advantage, and the rest of the steps are basically "read and follow all label instructions" type stuff. I'm guessing you can turn up a paper clip somewhere, and acquiring a basic digital voltmeter (under $20) can be beneficial in many projects, automotive or not.

 

I'll likely give it a try taking my time and following your instructions closely. Sometimes I get a little paranoid about screwing something up and creating a new problem that I didn't have before, but it doesn't appear too complicated like you said. Thanks.

 

OK, I am trying to test my TPS also because I got a code 22. I hate to sound stupid but what should I set the multimeter to when checking this?? With the key to run and testing the top two wires with jumpers I haven't seen anything close to .57 come up on the multimeter.
Thanks

 

I'm trying to diagnose my IAC problem, and according to the 1991 Shop manual, the reset procedure is different and a lot less complicated than what's outlined here. It says to just depress the gas pedal slightly and then start the engine. Run for 5 seconds and shut off. The IAC is now reset.
Is there a difference in the way the '730 handles the IAC from the '165? Doing the steps that Vader posted yeilds no movement from the 2 different IAC motors.

 

With the three wires, there are 3 different ways to check, across two wires.
Top to bottom, middle to top, and middle to bottom.

Across two of the wires (still hooked up to TPS, key on) 4.5 volts or so. Steady. Ground to 5 volts DC. (same plugged in or not)

Across the other two .54 volts (540 mv). Varies up to 4.5 with throttle depress. Should be a very smooth, linear sweep (used by computer).

Across other two 4.5 volts. Decreases to low volts when throttle is pressed. (not used for anything, but should also be smooth)

 

Just a quick follow-up. Had my base idle adjusted to 750 about two weeks ago and since then everything seems fine. Haven't put very many miles on since it's not a daily driver but it seems to have made a world of difference. Thanks everyone for all your help.