I have been trying to track down rough/searching at idle (posted previously). A likely culprit is the IAC but my impression is that there would be effects felt at other speeds as well since, for example, an IAC that is stuck open will still allow air throught the IAC inlet below the bores. Would this lead to rich/lean condition?. I ask this because since the bumpy idle has started, the car seems to feel different also at cruise speeds.

Are there any "backyard mechanic"-type checks that can be done to verify if the IAC is working? I am talking about the type of stuff you can do without scanners or voltage meters. I have heard that if you remove the IAC from the throttle body and turn the key on without actually starting, the pintel should move? What about checks with the IAC in place and the car running? I disconnected the electrical connector to the IAC at idle but did not hear a difference.

Or should I just bite the bullet and assume that with 50K miles on the car, buy a new IAC for $60 anyway?

Thanks,

Doug

 

Doug, try removeing the IAC valve and cleaning the carbon deposits out of the bore and throttle body opening. In the center of the throttle body between the butterflies is a bleed air opening that gets gummed-up. It is possible to clean the air bleed hole-up, remove carbon and correct the problem. It worked for me, at least until I installed a "Hotcam" and screwed the idle-up again!. Good luck and keep us posted :steering:

 

A faulty/dirty IAC can cause a idle problems as can a leaking EGR valve diaphram. The bad IAC effects will be felt mostly at idle but a leaking EGR valve can be felt at highway speeds and result in higher emissions.

To see if the IAC is moving, remove the IAC and place it into a zip-lock bag, jumper ALDL pins A & B with a paper clip, turn the key On and watch the IAC pintel to see if it extends. If it begins to extend, immediately turn off the ignition so it won't extend too far.

To test the EGR valve for a vacuum leak, carefully remove the vacuum line from the EGR valve, install a rubber vacuum tube with a T. Connect one T section to say the FPR vacuum source at the plenum and the other T section to a vacuum gauge (AutoZone has the vacuum hose, Ts and a vacuum gauge). Start the engine and, after the EGR valve opens, pinch off the vacuum hose to the plenum. This if the vacuum reading drops either the EGR valve diaphram is leaking or there is a leak in your new vacuum connections.

 

I have a 1995 that has the 16-pin ALDL connector rather than the 12-pin type. I don't think shorting the pins works the same way (i.e., my service manual shows both ALDL connector types but states that codes can be shown only with the 12-pin type by shorting A-B--there is no equivalent for the 16-pin type). However, I wonder if pintel movement can be seen by disconnecting the IAC from the throttle body (but keeping the electrical connection intact) and just turning the key on and off.

 

I too have a '95. You can display codes on the LCD speedo readout by taking a bent paper clip and shorting pin #4 to pin #12 on the 16 pin ALDL. Once you've got the bent paper clip slid into pin 4 and 12, turn the key to "on" such that the fuel pump spins up but do not crank the engine. The codes will display on the speedo. There are 4 or 5 modules on a '95 that will display codes, 1, 4, 9, and "A". Module 7 below may also display if your car has selective ride control shocks installed (?)



Brief summary of the procedure:


You short pin "12" to pin "4" and turn the ignition switch to "On" without starting the engine.

The speedometer will display any codes using the same protocol as the 1990-1993 model but there are some changes in the designation for the modules plus additional modules are added:

Module "1" is still the CCM module.

Module "4" is now called the PCM module (Powertrain Control Module) because automatic transmission computer control was added to Engine Control Module in 1994.

Module 7 (on the 1996 model only) is the RTD module. (This is the Real Time Dampening module which replaced the Selective Ride Control module in 1996).

Module 9 is the ABS/ASR module number from 1994 through 1996.

Finally, Module "A", the DERM (Dynamic Energy Control Module --- (the air bag control module) will be requested to show any codes.

Just like the 1990-1993 display, you read the codes on the speedometer (big) and read the module number on the trip odometer (small).
A series of dashed lines for instance --- indicates no more stored codes for that module.

A code showing as C12 for the CCM module (module #1) means no codes are stored. So C12 is a good thing to see.

Again, you can cause the codes to repeat by turning the ignition off for five seconds and then back on. Turn the ignition off and remove the short to restore normal operation.

To clear codes in the CCM proceed as follows:

1. With ignition "off" ground terminal #12 of the DLC (use bent paper clip to connect pin 4 to pin 12)

2. Turn ignition "on".

3. Press trip/odo button on the DIC until 1.7 appears in the trip
monitor area of the instrument cluster.

4. Press eng/met button on the DIC & hold until "---" appears in the
speedometer area of the cluster, this will clear CCM DTC'S.


To clear PCM/ECM codes do the following:


1. Press the trip reset button on the DIC until the desired system is displayed. In this case it will be 4.0.

2. Press trip/odo button on the DIC until the desired diagnostic mode(4.7) is displayed on the trip monitor area of the cluster.

3. Press & hold the eng/met button on the DIC until "---" is
displayed in the speedometer area of the cluster, this will clear PCM codes.


To clear ABS/ASR codes do the following:

Same as above but you’re looking for on the trip odo

P.S. If the problem still exists the code(s) will return after engine operation


94/95 OBDI LT1 DTCs:

DTC 11 - Malfunction Indicator Lamp (MIL) Circuit
DTC 13 - Bank I (Left) Heated Oxygen Sensor (HO2S) Circuit (Open Circuit)
DTC 14 - Engine Coolant Temperature (ECT) Sensor Circuit ( Voltage Low, High Temp)
DTC 15 - Engine Coolant Temperature (ECT) Sensor Circuit ( Voltage High, Low Temp)
DTC 16 - Distributor Ignition System (Low Resolution Pulse)
DTC 18 - Injector Circuit(s)
DTC 21 - Throttle Position (TP) Sensor Circuit (Signal Voltage High)
DTC 22 - Throttle Position (TP) Sensor Circuit (Signal Voltage Low)
DTC 23 - Intake Air Temperature (IAT) Sensor Circuit ( Voltage High, Low Temp)
DTC 24 - Vehicle Speed Sensor (VSS) Circuit
DTC 25 - Intake Air Temperature (IAT) Sensor Circuit ( Voltage Low, High Temp)
DTC 26 - Evaporative Emission (EVAP) Canister Purge Solenoid Valve Circuit
DTC 27 - Exhaust Gas Recirculation (EGR) Vacuum Control Signal Solenoid Valve Circuit
DTC 28 - Transmission Range (TR) Pressure Switch Assembly Fault
DTC 29 - Secondary Air Injection (AIR) Pump Circuit
DTC 32 - Exhaust Gas Recirculation (EGR)
DTC 33 - Manifold Absolute Pressure (MAP) Sensor Circuit ( Voltage High - Low Vacuum)
DTC 34 - Manifold Absolute Pressure (MAP) Sensor Circuit ( Voltage Low - High Vacuum)
DTC 36 - Distributor Ignition System (Faulty High Res. or Extra Low Res. Pulse Detected)
DTC 37 - Brake Switch Stuck "ON
DTC 38 - Brake Switch Stuck "OFF
DTC 41 - Ignition Control (IC) Circuit (Open Circuit)
DTC 42 - Ignition Control (IC) Circuit (Shorted or Grounded Circuit)
DTC 43 - Knock Sensor (KS) Circuit
DTC 44 - Bank 1 (Left) Heated Oxygen Sensor (HO2S) Circuit (Lean Exhaust Indicated)
DTC 45 - Bank 1 (Left) Heated Oxygen.Sensor (HO2S) Circuit (Rich Exhaust Indicated)
DTC 46 - PASS-Key Circuit
DTC 47 - Knock Sensor (KS) Circuit or Module Missing
DTC 48 - Mass Air Flow (MAF) Sensor Circuit
DTC 50 - System Voltage Low
DTC 51 - EEPROM Programming Error
DTC 53 - System Voltage High
DTC 55 - Fuel Lean Monitor
DTC 58 - Transmission Fluid Temperature (TFT) Sensor Circuit Low (High Temp )
DTC 59 - Transmission Fluid Temperature (Low Temperature Indicated)
DTC 61 - A/C System Performance
DTC 63 - Bank 2 (Right) Heated Oxygen Sensor (HO2S) Circuit (Open Circuit)
DTC 64 - Bank 2 (Right) Heated Oxygen Sensor (HO2S) Circuit (Lean Exhaust Indicated)
DTC 65 - Bank 2 (Right) Heated Oxygen Sensor (HO2S) Circuit (Rich Exhaust Indicated)
DTC 66 - A/C Refrigerant Pressure Sensor Circuit (Open or Shorted)
DTC 67 - A/C Refrigerant Pressure Sensor Circuit (Pressure Sensor Activity)
DTC 68 - A/C Relay Circuit (Shorted Circuit)
DTC 69 - A/C Clutch Circuit
DTC 70 - A/C Clutch Relay Driver Circuit
DTC 71 - A/C Evaporator Temperature Sensor Circuit
DTC 72 - Vehicle Speed Sensor Loss
DTC 73 - Pressure Control Solenoid (PCS) Circuit (Current Error)
DTC 74 - Traction Control System(TCS)CircuitLow
DTC 75 - Transmission System Voltage Low
DTC 77 - Cooling Fan Relay Control Circuit
DTC 78 - Fan control PCM terminal A10
DTC 79 - Transmission Fluid Overtemp
DTC 80 - Transmission Component slipping
DTC 81 - Transmission 2- 3 Shift Solenoid Circuit
DTC 82 - Transmission 1-2 Shift Solenoid Circuit
DTC 83 - Reverse Inhibit System (Manual Transmission)
<<<<<<<<<select>>>>>>
DTC 83 - TCC/PWM (Auto Trans)
DTC 84 - Automatic Transmission 3-2 Control Solenoid Circuit
<<<select>>>>>>
DTC 84 - Skip Shift Solenoid Circuit (Manual Transmission Only)
DTC 85 - Transmission TCC Stuck "ON
DTC 90 - Transmission TCC Solenoid Circuit
DTC 91 - Skip Shift Lamp Circuit
DTC 97 - VSS Output Circuit
DTC 99 - Tach Output Circuit





[Modified by Lone Ranger, 6:39 PM 3/28/2004]

 

In answer to the question about stuck IAC causing rich or lean condition, the oxygen sensors should see rich or lean and so the PCM will add or pull fuel in an attempt to compensate.

By the way, Oxygen sensors that are lazy or going south can cause some idle un evenness and also would cause symptoms at part-throttle operation, most likely a slightly rich condition. If your mpg mileage has dropped, I would look at oxygen sensors before i would look at IAC.

 

Hey Lone Ranger--thanks for the info. I guess the hardest part is getting in a position to even see the ALDL so that a paper clip can be inserted. I have a Hypertech Power Programmer that came with a cable that plugs into the ALDL on one end (I always do this by feel rather than site). The other end of the cable looks like a typical serial-port type computer cable and I wonder if it is easier to do the shorting on that end (although I do not know what the pinouts are). By the way, where did you find all that useful info?

 

You just have to be flexible and you can put your eyes on the ALDL. I would think the hypertech cable might change the pinout config but who knows. Found the info hannging out on the forum...

 

I finally got around to trying the 4-12 jumper short on my ALDL which was an interesting discovery. No codes showed up for any of the modules. I also tried the IAC test by shorting 4-12 and turning key on but not starting. I could barely notice any movement in the pintel, even if keeping the key on for a while and also by turning the key on and off. I should mention that while I had the IAC electrical connection hooked up, I had disconnected the throttle position connector to provide better access to the IAC screws--I do not know if the tps needs to be connected for the IAC to work.

I also tried moving the pintel by hand but did not want to force anything. Gentle pressure pushing in or out results in no movement--is this supposed to be moveable by gentle manua pressure?

Anyway, I wonder if any of this indicates that it is time to replace the IAC. I guess it is cheap enough even if not needed.

Doug