Intake

All engines need to breathe, and the engine in your E30 is no different. You need oxygen to make an explosion. Fuel + Air + Spark = Power.

Since the majority of E30s use petrol injection engines, this page describes injection intake systems.

For the Turbo Diesel engine, jump to the Turbo section of this page or learn more about forced induction.

For M10 engines and other carburettor systems, please refer to the M10 page.

Overview

Contrary to popular belief, when you press the accelerator pedal, you're not controlling your fuel input. You're actually controlling the air input, and based on that the engine puts in fuel to match, at a ratio determined by the ECU. The ECU takes its readings from a number of sensors around the Intake system, as well as the Exhaust system on later engines.

The natural sucking effect of an exploding engine is called Natural Aspiration, and is directly opposed to having the air forced into the engine by way of a turbo or supercharger, known as Forced Induction.

Air enters the system through an air filter, located behind the passenger side headlight. This is bolted directly to the AFM, a sensor that measures air flow. The air is carried from here by a rubber boot, which distributes air flow to the intake manifold in one of two ways. If the engine is idling, a small amount of air is allowed into the engine by way of an Intake#ICV, which is directly controlled by the ECU. The moment the throttle pedal is pressed, the ICV is switched off and the Throttle Body takes over, a mechanical door directly connected to the throttle pedal by a cable. The ECU senses that the throttle body is open by the TPS mounted underneath.

Once the air enters the intake manifold, its entry into each cylinder is controlled by valves within the engine head. As it enters the cylinder, it is mixed with fuel and ignited. The waste gas is then ejected through more valves into the exhaust system.

In later systems fitted with a lambda sensor, this exhaust gas is analysed for oxygen to more accurately control fuel economy and protect the exhaust system.

Components

Throttle Position Switch

The Throttle Position Switch (TPS) is a three-pin switch, and is bolted to the bottom of the throttle body. When the throttle pedal is untouched, the throttle body is closed and the TPS reads Throttle Closed, thus informing the ECU to activate the idle control valve. As soon as the throttle pedal is touched, the TPS should click, indicating that it is reading open throttle and that the ECU should now read from the AFM. If the throttle pedal is fully depressed, the TPS will read Wide Open Throttle (WOT) and the ECU will adjust fuelling accordingly.

The TPS is driven by the shaft that runs through the middle of the throttle body, and is held in place with two screws. However, to access the TPS, the throttle body must be removed.

Because of the oil recapture system in BMW engines, it is possible for the TPS to become gunked up over time with oil, which will stop it working. A dirty or damaged TPS is the source of many intake problems.

ICV

The Idle Control Valve, or ICV, can be thought of as an electric door; it spins around at a certain rate, blocking and opening the passage so that only a specific flow of air can pass through it. It activates as soon as the ignition circuits are turned on, and should make a light buzzing noise.

The ICV is active when the TPS reads Throttle Closed.

Lambda

The Lambda sensor is an oxygen sensor, mounted in the down pipe. If oxygen is detected, the ECU adds more fuel so that no air goes unused. If no oxygen is detected, the ECU lowers the fuel quantity until oxygen is again detected.

Turbo

:Main article:

A turbo is a pair of fans or screws used to force more air into an engine. The first fan uses the exit velocity of the exhaust gas to spin up, which in turn drives the second fan which pushes air into the other side of the engine. This is known as Forced Induction.

The only Forced Induction model of E30 is the 324td. However, it is possible to mount a turbo to any E30 engine, although some are better suited than others.

Be advised that installing a turbo is an extremely costly project requiring extensive modification to both the Intake and Exhaust system, as well as significant strengthening of the Engine internals.

Upgrades

K&N Filter

Replacing the existing air filter with a bolt-on aftermarket one is a cheap and popular modification to E30 engines, but Zone opinion is very heavily weighted against them. The standard BMW filter is more than adequate for standard engines, and replacement filters will only be needed after severe modifications to the rest of the engine.

Throttle Bodies

Replacing the existing throttle body with another is a good way of getting more air into the engine. Unfortunately, there are no easy, bolt-on options through the standard E30 range, but with a little bit of grinding it is possible to fit a 325i throttle body to a 320i engine. Learn more about converting your throttle body.

If you already have a 325i throttle body, and the rest of the M20B25 engine that does with it, the next step is an aftermarket upgrade known as a Big Bore Throttle Body, or BBTB. Learn more about BBTBs. [[Intake#