Removing M42 Throttle Body Heater

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Like most BMW engines from the period, the M42 features a throttle body heater. Using a pipe line from the cooling system, hot water is channelled into a plate attached to the throttle body to prevent it icing up in cold weather.

However, here in the UK we don't get the sort of temperatures that make that necessary, and since colder air is better for the engine you should see an increased throttle body response by ditching the system and re-routing the plumbing. Here's how.

A lot of the pipes used here are leftovers from an E36 M42 installation, cut to fit, which means no part numbers are provided. Be creative.

1. Drain the coolant. You don't need to drain it all but if you don't lower the level then coolant runs out of the engine and makes everything wet. If you are wearing latex gloves like I was then it only increases the chance you will drop something into the inlet manifold.

2. Remove top half of air box, AFM and throttle body.

3. Remove upper part of inlet manifold.

4. Remove pipes.

5. Remove lower inlet manifold. I left the fuel lines attached and moved it just enough to reach the plastic pipe on the block (marked X in this diagram).

6. Remove the hose that feeds hot water up to the throttle heater (part 18 in the diagram above) from the plastic pipe on the side of the engine .

7. Replace this pipe with the one from the same position on an E36. Cut off the last 90° bend from the top. Part number is 11511739245 (needs checking). This hose has an 16mm opening at the end that connects to the plastic pipe and 10mm where it connects to the block.

8. With the 90° bend cut off the 10mm end you can now fix this hose with Jubilee clips from the plastic pipe to the metal stub between cylinders 2 and 3.

9. Refit lower manifold.

10. Refit upper manifold and put the TB in place but not fixed. This makes connecting the rest of the hoses easier. I installed a new gasket.

11. Route a hose from the front of the engine to the brass stub on the underside of the TB. I used the original E30 hose at the front of the engine (A in the photo), one straight connector and a piece of E36 hose from my scrap box (B in the photo).

12. The ICV needs a hose routed from the back of the engine to the rubber boot attached to the TB. I used one length of E36 hose cut down (C in the photo) and a straight connector into the boot . I don't have a part number for this piece.

13. Refit TB, boot and airbox.

14. Refill with coolant. Get up to temp and bleed.