BMW E36 rough idle and hesitation

The most common causes are an intake-side air leak, a dirty or faulty idle control valve, a faulty lambda sensor and the crankshaft position sensor. Read the fault codes first and check the cheapest things before replacing expensive parts.

First check the accordion boot between the air flow meter and the intake manifold, plus the other air hoses and connectors. A cracked boot, a loose hose or the crankcase vent diaphragm can easily leak. The leak may be small. If the revs rise clearly when you spray starter fluid under the intake manifold, you have found the leak.

Remove the valve, clean it with brake cleaner and blow it through with compressed air. No gaskets are needed. A good valve lets air through and rattles when shaken. Measurement: between pins 1 and 2 and between pins 2 and 3 the resistance is 20 ohms, between pins 1 and 3 it is 40 ohms, tolerance +/- 5 ohms.

Yes. A faulty lambda sensor can make the idle fluctuate and the fuel consumption gauge swing. The crankshaft position sensor can give a wrong signal and cause hesitation in a certain rev range. After replacing the lambda sensor the fault memory must be cleared.