Number: 87-100

Section: 6E

Date: APRIL 1987

Subject: THROTTLE BODY CARBON BUILDUP

Model and Year: 1985-87 CAMARO, CORVETTE WITH 5.0L
                            OR 5.7L PFI ENGINE (VIN CODES F AND 8)
TO: ALL CHEVROLET DEALERS

Some 1985-87 vehicles may experience the following:

1. Code 34 on restart.
2. High idle speed.
3. High accelerator pedal effort.
4. Engine stalls at idle or during deceleration.
5. Rough/low idles.

These conditions may be caused by carbon buildup inside the throttle body bores behind the throttle plates limiting air flow. It should be noted that what appears to be just a small amount of accumulation can be enough to limit air flow.

To diagnose this condition, perform the following steps:

1. Measure minimum idle speed using procedures defined in Section 6E3 of the Shop Manual.
2. If minimum idle speed is less than specified in chart, proceed to Step 3. Otherwise, perform activities defined in the Shop Manual under Section 6E3, Section B Rough, Unstable or Incorrect Idle, Stalling.
3. Remove negative battery terminal.
4. Remove mass airflow duct at throttle body.
5. Cover TPS and IACV to protect from overspray
6. Stuff IACV air inlet passage with shop towel to prevent cleaner from entering passage (See Illustration).
7. Block throttle lever in wide open throttle position.
   *NOTICE: THE CHEMICALS USED IN CARBURETOR CHOKE CLEANERS ARE VERY STRONG. DIRECT CONTACT WITH ANY RUBBER OR PLASTIC PARTS WILL CAUSE SWELLING, CRACKING, OR OTHER DAMAGE. DO NOT USE ANY CLEANER THAT CONTAINS METHYL ETHYL KETONE, WHICH IS AN EXTREMELY STRONG SOLVENT, AND NOT NECESSARY FOR REMOVAL OF THIS TYPE OF DEPOSIT.
8. Spray carburetor choke cleaner around throttle bore (s) and on back side of throttle valve(s). Avoid spraying directly at throttle shaft bearing surfaces to prevent washing out factory lubrication.
9. Use a nylon parts cleaning brush or shop towel to remove heavy deposits. (It should be noted that what appears to be just a small amount of accumulation, can be enough to limit airflow).
10. Release throttle lever. Open and close throttle lever several times to make sure it operates freely.
11. Remove shop towel from IACV air inlet passage, and uncover TPS and IACV.
12. Connect mass airflow duct to throttle body.
13. Connect negative battery terminal.
14. Check minimum idle speed, and readjust speed and TPS as specified in the following chart:

* Distributor Connected     ** Disconnect the distributor set-timing connector.
Labor Operation Number: T1205
Labor Time :0.6 Hours