Min Airflow

MINIMUM THROTTLE BODY (TB) POSITION (NON-ADJUSTABLE)
It is extremely unlikely that this adjustment will ever be necessary on a TB that has not been tampered with after production! If idle revolution per minute is low, you may need to replace the TB to correct the low idle speed.

MINIMUM THROTTLE BODY (TB) POSITION CHECK
The minimum throttle body (TB) position (throttle stop screw) adjustment should not be considered the "minimum idle speed", as on other fuel injected engines. Low internal friction and provision for slight production variations and various operation altitudes resulted in a calibrated minimum TB position which is too low to allow most engines to idle. The adjustment is preset at the factory and no further adjustment should be necessary.

If there is a complaint of high idle speed, vacuum leaks should be considered the most likely cause. Because the Engine Control Module (ECM) "learns" Idle IAC, it is even less likely that a stalling complaint would be due to an incorrect minimum TB position. In either case, Diagnosis by Symptom and IAC valve check CHART C-2C should be referred to. Testing and Inspection

If it is determined that the minimum TB position is suspect, be sure IAC valve is not "lost" (not actually at the location indicated by current IAC "counts"). The IAC valve could be "lost" if ECM power has been interrupted with the ignition "ON", or the IAC valve has been disconnected with the engine running since the last reset, as described previously in this section in the "IAC Valve Assembly" general description.

The minimum TB position may be checked using the following procedure.

1. Block drive wheels, and apply parking brake.
2. Connect "Scan tool" to the data link connector.
3. Start engine and allow to reach operating temperature (about 90°C) and "Closed Loop".
4. A/T - shift to DRIVE ("D") and then back to neutral ("N").
5. Select power steering pressure switch input on "Scan tool". With air conditioning and all electrical accessories "OFF", transmission in neutral, "Scan tool" should read "OFF" or "NORMAL". (If not, refer to CHART C-1 E to diagnose and repair faulty power steering pressure switch circuit before proceeding). Allow idle to stabilize. Testing and Inspection
6. Select IAC valve display on "Scan tool", and read IAC valve counts. If between 5-45 counts, the minimum TB position adjustment is acceptable. It is important to allow idle speed to stabilize to assure correct counts are determined.

If counts in step 6 are too low, check for intake air (vacuum) leaks at hoses, TB and intake manifold or damaged throttle lever and correct as necessary. Also, refer to CHART C-2C "Diagnostic Aids". If no vacuum leaks or other cause of excessive air into the intake are found, it may be necessary to replace the TB to correct the low idle speed problem. Refer to "TB Replacement" in this section.

If counts in Step 6 are too high, check for damaged throttle lever or airflow restriction by the TB. If no problem is evident, remove inlet air duct at the TB, and clean residue from inside of TB bore and from edges of TB using carburetor cleaner and a shop towel. (Do Not use a cleaner that contains methyl ethyl ketone. It is an extremely strong solvent, and not necessary for this type of deposit). Re-check "Scan tool" IAC valve counts, per the preceding procedure.

If counts are still too high it may be necessary to replace the IAC valve or the TB assembly, If no vacuum leaks are indicated or engine loads are present.