General Information The idle quality test allows more in-depth diagnosis of such engine complaints such as rough idle, missing when idling, or delayed starting time. The test scope is divided into: Idle quality, engine speed per cylinder, Idle quality, burn time per cylinder, Idle quality, while starting. The methods for using each test sequence are explained on the following pages. It is necessary in all three test sequences to evaluate the tabular examples and/or the graphic examples. The two should be compared and checked for agreement. When evaluating the idle quality measurement, the following should be noted according to the number of cylinders the engine has:

Engine Speed per Cylinder

The "Engine Speed per Cylinder" table clearly shows that the cylinder with the lowest engine speed is the weakest. As a result, the measured value is well suited as a confirmation in cases of frequent missing which can not be identified with certainty by use of the engine speed graphic example. Since these values represent an average of individual values, intermittent missing can not be identified. Intermittent misses can only be identified and evaluated by means of the sample graphic illustration. Before starting repair work based on test results, the vehicle should be evaluated from the driver's seat and compared to typical production vehicles. (Vehicles with automatic transmissions should be evaluated with the transmission in a drive range.) In such a case, test results can not replace individual judgment and the experience of a specialist. a) 4-cylinder engine, example 1 In principle, the average engine speed change or average engine speed difference measurements should not be used to diagnose 4-cylinder engines for reasons of measuring technique. The reason is: The average speed change value of a properly functioning cylinder can indicate a high speed drop of the following cylinder, thereby leading to a false diagnosis. In case of a failure, the average speed change value on 4-cylinder engines can not clearly indicate the defective cylinder.

Engine Speed per Cylinder

Idle quality table - Engine 102/111, Example 1

Cylinder	Average engine speed	Average engine speed change
1	785	1
3	776	- 9
4	784	8
2	784	0
Max	785
Min	776
Difference	9

Note: Brief or intermittent misfires can not be recognized from the table, for this purpose, the scope pattern must be used to identify the defective cylinder. The column "Average engine speed change" must not be used for the evaluation. A clear statement is only possible via the Average engine speed.

Engine Speed per Cylinder


Table Idle quality - Engine 102/111, Example 2

Cylinder	Average engine speed	Average engine speed change
1	999	5
3	994	- 5 Incorrect reading
4	976	- 18 Defective cylinder
2	994	18
Max	999
Min	976
Difference	23

Note: Brief or intermittent misfires can not be recognized from the table, for this purpose, the scope pattern must be used to identify the defective cylinder. The column "Average e purpose, the scope pattern must be used to identify the defective cylinder. The column "Average engine speed change" must not be used for the evaluation. A clear statement is only possible via the Average engine speed.

Engine Speed per Cylinder


Table Idle quality - Engine 102 with Tandem Mass Flywheel, Example 3

Cylinder	Average engine speed	Average engine speed change
1	753	- 1
3	750	- 3
4	739	- 11 Defective cylinder
2	754	15
Max	754
Min	739
Difference	15

Engine speed per cylinder

c) 6-Cylinder engine, Engine 103 In the example shown in the table below, the average engine speed for cylinder 6 is the lowest. The average engine speed change at cylinder 6 is clearly the greatest and can be used for the evaluation. The engine speed drop is also clearly visible in the scope pattern.

Table Idle quality

Cylinder	Average engine speed	Average engine speed change
1	727	14
5	728	1
3	726	- 2
6	670	- 56 Defective cylinder
2	698	28
4	713	15
Max	728
Min	670
Difference	58

Engine Speed per Cylinder

d) 8-Cylinder engine, Engine 116/117 In principle, the average engine speed change or average engine speed difference value measured should not be used for diagnosis of 8 cylinder engines. Cause: The engine speed difference value can indicate an excessive engine speed drop on the cylinder following a strong cylinder, thus leading to a faulty diagnosis. The engine speed difference value can not be traced with certainty to the defective cylinder . In the example shown in the table, the average engine speed for cylinder 6 is the lowest. However, the average engine speed change for cylinder 8 is the greatest. Since the greatest engine speed drop occurs at cylinder 8, cylinder 8 is the defective cylinder. Cylinder 6, which follows, is affected by cylinder 8 and should be ignored.

Table Idle quality

Cylinder	Average engine speed	Average engine speed change
1	704	4
5	712	8
4	720	8
8	686	- 34 Defective cylinder
6	668	- 18 Effect from cylinder 8
3	684	16
7	695	11
2	700	5
Max	720
Min	668
Difference	52

Engine Speed per Cylinder

e) 8-Cylinder Engine, Engine 119
Table Idle quality

Cylinder	Average engine speed	Average engine speed change
1	658	3
5	656	- 2
4	660	4
8	658	- 2
6	659	1
3	656	- 3
7	660	4
2	655	- 5
Max	660
Min	655
Difference	5

Engine Speed per Cylinder

f) 12-Cylinder Engine, Engine 120
Table Idle quality

Cylinder	Average engine speed	Average engine speed change
1	664	6
12	658	- 6
5	663	5
8	659	- 4
3	665	6
10	660	- 5
6	665	5
7	658	- 7
2	664	6
11	658	- 6
4	663	5
9	658	- 5
Max	665
Min	658
Difference	7

Engine Speed per Cylinder

f) 12-Cylinder Engine (Engine 120)
Table Idle quality
Cylinder 4 defective (right bank)

Cylinder	Average engine speed	Average engine speed change
1	716	11
12	712	- 4
5	723	11
8	721	- 2
3	732	11
10	730	- 2
6	740	10
7	734	- 6
2	743	9
11	737	- 6
4	730	- 7 Defective cylinder
9	705	- 25 Effect on following cylinder
Max	743
Min	705
Difference	38

Engine Speed per Cylinder

f) 12-Cylinder Engine, Engine 120
Table Idle quality

Cylinder 10 defective (left bank)

Cylinder	Average engine speed	Average engine speed change
1	743	11
12	739	- 4
5	748	9
8	744	- 4
3	752	8
10	734	- 18 Defective cylinder
6	722	-12 Effect on following cylinder
7	717	- 5
2	727	10
11	724	- 3
4	735	11
9	732	- 3
Max	752
Min	717
Difference	35

Burn Time per Cylinder
(only with Bear engine analyzer)

This test is intended as an initial measurement similar to the idle quality test. Positive or negative variations, which always occur at the same cylinder, indicate a problem in the ignition system which will not always necessarily result in an engine speed drop. However, engine missing may occur at higher mileage. Burn time per cylinder, Engine 104/111 HFM-SFI can be tested with HHT starting 01/94. Major positive or negative variations may be caused by carbon fouled spark plugs (e. g. short-distance driving). The vehicle should be driven for a longer distance to obtain a more exact diagnosis. The variations shown in the table do not result in an unacceptable engine speed drop.

Table Idle quality, Engine 102

Cylinder	Average engine speed	Average engine speed change
1	683	- 4
3	684	1
4	686	2
2	687	1
Max	687
Min	683
Difference	4 - Difference value still acceptable

Burn Time per Cylinder

Variations >± 0.5 ms per cylinder should be confirmed by additional measurements such as oscilloscope and secondary ignition system table.

While Starting

The program " Idle Quality " can be used as a " Starting Test " to quickly isolate leaking injection valves. Preconditions: Warm up engine to at least 80 °C engine oil temperature. Shut off engine for at least 15 minutes. Observe "Complaint related notes" Select idle quality program, the program "Idle quality". Starting test appears only when engine is turned off. Start engine and follow instructions displayed on engine analyzer. The idle quality table must not be used for analysis. The fault indications can only be determined from the scope pattern (see example 4-, 6- and 8-Cylinder engine).

The example shows a 4 cylinder engine
Idle quality table, Engine 102

Cylinder	Average engine speed	Average engine speed change
1	1056	17
3	1051	- 5
4	1047	- 4
2	1039	- 8
Max	1056
Min	1039
Difference	17