madmike

Hope you guys and girls can help. I cleaned my throttle body, took the iac off squirted and cleaned it with throttle body cleaner. Put it all back together. adjusted the IAC by jumping the A/B connector, turned motor to on, waited one minute, disconnecting the IAC, Adjusting the idle to 450 rpm,turned motor off, replugged the IAC, and took the paperclip out. My idle is slightly rough. I checked the plug(all my clips on the IAC plug were broken previously) and the plug was able to plug in the IAC in two positions. I know it has litlle plastic stops that stop it from being plugged in improperly but if I plugged it wrong, would i damage the IAC if I ran the vehicle? I think I did plug it in wrong because I studied the plastic stops and they didnt match the first time I plugged it in. Hellllp :banghead:

AGENT 86

What year motor ??
:cheers:

AGENT 86

I had the same problem awhile back.
Kevin had the answer. Check it out http://forums.corvetteforum.com/zerothread?id=641712
:cheers:

madmike

Thanx agent , i will get right on it. I printed out the post and will see what happens. By the way its a 1987 tpi motor. Thanx again everyone for the help :party:

Sam Lam

Madmike: When you adjust the base idle, you should unplug the timing connector. Unless you do this, the computer will adjust the timing in an attempt to get the desired RPM. The GM Helms manual has this step in bold print. Suggest you readjust the base idle speed.

Midnight89

Madmike-- Great timing for this post...I'm going to have to do the same to my 89 this weekend.

Sam Lam-- I new to all of this stuff, but I did notice that this step wasn't included in the TechTip (while it is scattered through some of the posts in the archives). When you say to unplug the timing connector; What is the timing connector and where is it located? Is this a piece that I can simply unscrew? And finally, do I unplug the timing connector BEFORE I start the motor up to set the base idle?

madmike

Wow i never thought about unplugging the timing thingie. I didnt see it either in any of the million instructions I have :banghead: My engine runs a heck of alot better though. I recleaned the IAC and CONNECTED IT CORRECTLY. By the way, a good trick to clean the plenum is of course spraying it intensly with throttle body cleaner but also afterwards spray it intensly with Simple Green degreaser letting it soak in and hosing it off. Anyway the car runs smoothly now. I will recheck the idle with the timing unplugged. Location of the timing plug is left of the Brake booster if your facing the cab and slightly below the distributor. Thanx all for the help. you guys came through again. Party time. :party:

86PACER

It is the Electronic Spark Timing connector "EST". It is located against the fire wall on the driver's side to the LEFT of your wiper motor housing, and to the RIGHT of your brake booster assembly, near your fuel pump relay. One of the wires is brown. The color of the wires are mentioned in the Emissions Label on the left side of the radiator shroud near the upper radiator hose.

This connector needs to be disconnected when adjusting timing to allow the engine to operate in the bypass timing mode. :thumbs:

madmike
The IAC connector should be plugged in with the edge that has the broken off clip facing DOWN to the ground. :thumbs:


[Modified by 86PACER, 12:46 AM 3/10/2004]

Sam Lam

Guys: I too am new to Vettes (2 years) and have tried to read all I can on articles to make my car run better. One of the first things I did was to buy the Helms GM manual (http://www.helminc.com/helm/homepage.asp). This cost me about $100 and I have paid for this many times usning the manual. I actually tried to get the base idle tech article changed by contacting the author.....and did correspond with him. No luck with the change! I attempted to get the article changed by contacting the moderator and again no luck. Sorry you have to learn things like this.
SAM

Jloshotz

:iagree: :iagree: :iagree:
I once many years ago uneedingly replaced a timing chain set because i didn't know this connector existed..... :mad I'd put a light on it and all i saw was the timing mark bouncing all over the place and immediately assumed it was the chain..... :banghead: Don't laugh at me too much on this one guys, this was on an 84 Trans am back in 88. Ah, to be so young and foolish again... :jester


[Modified by Jloshotz, 11:55 PM 3/10/2004]

Sam Lam

Here are the "revised" instructions on how to set the base idle for a 89 Vette:

Corvette 1989 - 350 TPI Engine
Setting Base Idle Speed (using 89 GM Helms Manual)

If this has not been done on your car before, the adjusting screw will be covered by a pressed-in plug. It’s located on the driver’s side of the throttle body. Remove this plug by using a small punch. Impact the plug on the side of its face and this will allow its removal.

1. Start the car and let the engine warm up to its operating temperature. (It is suggested that you make sure the timing of the engine is set to specification prior to doing this procedure.) During this step, the engine should be in closed loop operation and all electrical accessories INCLUDING COOLING FANS should be off. Shut off the engine after it is warmed up.

2. Turn ignition switch to ON, but do not start engine. Adjust the Throttle Position Sensor to .54 +/- .08 volts using a digital meter. There are 3 wires stacked vertically on the TPS. You will need to be able to measure the voltage between the two top wires. You can either buy a special harness connector that breaks these wires out (from Mid America costing $12), or gently pierce the insulation of the wires with the pointy prongs on your voltmeter. You can also stick a paper clip into each of the two top locations of the connector and clamp onto the paper clips to measure the voltage. The adjustment is accomplished using a Torx driver and loosening the two screws that hold the TPS to the throttle body. Then rotate the sensor either clockwise or counter clockwise (with the ignition on and engine not running) to obtain the .54 volt specification. Retighten the two TPS Torx screws to “lock in” the adjustment.

3. With the IAC connected and the ignition “OFF,” insert an Auto Zone tool (free upon request from Auto Zone) into the diagnostic connector (ALDL) terminals “A” to “B.” (These are the upper right two holes in the connector.) This grounds the ECM and places it into the diagnostic mode.

4. Turn the ignition to the “ON” position without starting the engine. Wait 30 seconds before doing step 5. Doing this forces the IAC pintle to the closed position (closes air passage) within the throttle body.

5. With the ignition still in the “ON” position, disconnect the IAC connector at the IAC valve. This action prevents the ECM from controlling the idle speed using the IAC valve.

6. Turn ignition switch off!

7. Remove the Auto Zone tool from the diagnostic connector.

8. Disconnect the timing connector located just behind the left valve cover. This is necessary to prevent the ECM from attempting to adjust the timing as you adjust the idle speed.

9. Start the engine. The idle speed will be really low, and you may have to coax the engine using the gas pedal or your hand and the throttle cable to keep it running. I find it useful to insert a small screwdriver between the end of the idle adjusting screw and the throttle body to keep the car running at this low idle point. HOWEVER, REMOVE THE SMALL SCREWDRIVER BEFORE MAKING THE FINAL IDLE ADJUSTMENT!!!

10. If your car is an automatic, set the parking brake and put the transmission in park. If your car is a manual, leave it in neutral.

11. Adjust the idle speed screw to obtain 425 +/-25 engine rpm. This will require a Torx tool to adjust the idle screw in the throttle body. As you adjust the idle screw to obtain the desire idle speed, you are changing the TPS voltage setting. The TPS will require re-adjustment in step 12. Make sure the cooling fans are not running while you make this adjustment.

12. Shut off the engine, re-connect the IAC and the timing connectors.

13. Turn on the ignition switch and do not start the engine. Reset the TPS to .54 +/-.08 volts as stated in step 2. Turn off engine.

14. Reset the IAC pintle position by:
a. Depress accelerator pedal slightly.
b. Start and run engine for about 5 seconds.
c. Turn off engine for 10 seconds.
d. Start engine and check for proper idle operation.

You are now in adjustment on base idle speed and TPS output. Start the engine. It may take a few minutes for the car to “catch on” or learn its new settings.

It should be stated that the throttle response from the engine can be increased by using a setting of .62 to .65 volts instead of the .54 specification. If desired, this change should be made after setting the base idle (using .54 volts).

I also set the timing on my 89 350 engine to 8 degrees before top dead center (BTDC). This setting along with the .65 volt TPS setting gives good throttle response. It is very difficult to start the car rolling, as it really wants to take off and run!!!

Revised by Bob Lamb 10/03 from a tech article written by Lars Grimsrud 10/01. These changes were required to align the Grimsrud article to the Helms GM manual for an 89 Corvette.

Use this as you wish as I have saved this on my puter as a reference!

SAM