Engine - Idle and Driveability Complaints
84BMW05GROUP 11 Engine
Bulletin 11 14 84 (936) Page 1 of 2
Montvale, NJ December 1984 Technical Dept.
SUBJECT: Diagnostic Procedure for Evaluation of Idle and Driveability Complaints
MODELS: All
Complaint: a. Rough idle
b. Poor initial driveability at high ambient temperature
c. Poor driveability after a hot soak
d. Surging at idle during warm-up
e. Idle lower than specifications only when A/C compressor is on
f. Surge at steady state throttle
g. Poor startability
Cause: There are obviously various causes for the above complaints but one significant influence is carbon accumulation on the intake manifold side of the intake valves. This build-up can become a factor on
^ M-10 Engines after 6,000-8,000 miles
^ M-20 Engines after 10,000-15,000 miles
^ M-30 Engines after 15,000 miles
Correction: Following the enclosed procedures for Diagnosis/Carbon Removal, based on the above mileage criteria, should simplify the diagnosis procedure and reduce shop comebacks.
Procedures: The following sequence should be used when evaluating all customer complaints stated previously:
1. Check ignition and fuel system using the BMW Service Tester. Replace failed fuel system components as appropriate. If ignition system problems are found refer to S.I. 12 04 84 (863) for upgrading secondary ignition system components.
2. On all M-20 and M-30 Engines install secondary ignition up-date kit per S.I. 12 06 84 (904) if not previously done.
3. If problem has not been corrected and the engine has accumulated the mileage stated under the Cause section of this S.I., remove intake manifold and inspect for carbon build-up. If carbon deposits are greater than 1 mm thick, the carbon should be removed prior to any additional diagnostic work. If carbon is present, currently you must carefully scrape the carbon from the intake manifold side of the valves. This can be done with the cylinder head installed by rotating the valves. Take care not to damage the valve seat surfaces while scraping.
Note: In the near future (January-February '85) BMW will have available a walnut shell blaster which will significantly reduce the time and effort required to clean carbon from the valves. (i.e. cylinder head removal will no longer be necessary).
4. While cylinder head is removed check valve guide stem seals and valve seating. Repair/replace as necessary.
5. Only after steps 1-4 should you proceed with other solutions for these driveability complaints (i.e. summer complaint summary S.I. 05 02 84 (841)) or diagnosis of individual components.
Customer Relations
Information: A) The carbon build-up on the intake manifold side of the intake valves can have two (2) sources. The main source is from the fuel itself. The gasoline oxidizes, leaving a carbon layer on the back side of the valve. The other source is from excessive oil which may leak past the intake valve guide seal and oxidize on the back side of the intake valve. It is very difficult to differentiate between the two sources of the build-up and possibly it is a combination of both sources. The rate of build-up can be minimized by the customer in the following ways:
1. Adhere to proper quality and viscosity of oil as stated in the Owner's Handbook or S.I. 00 04 84 (890). Also, the customer should adhere to the oil change/maintenance intervals in order to minimize the contamination of the oil with subsequent wear of valve seals etc.
2. Use a gasoline with a high dispersency additive (similar to Chevron, Exxon and Shell).
3. Periodic use of "Techron" additive (refer to S.I. 05 02 84 (841)) in strict accordance with the manufacturer's instructions printed on the container.
Warranty
Status: Reimbursement for carbon removal will be provided through normal warranty processing under Defect Code 11 34 00 76 00 using the following qualifying conditions:
1. 36,000 mile/3 year standard Vehicle Warranty for all engines
2. 50,000 mile/5 year Emission Control Warranty for all engines