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Vacuum leak locations on E30 throttle body (M20)

January 1, 2022

In the vast majority of cases, vacuum leaks are to blame for poor or inconsistent idle issues on M20 engines found in E30’s.

Vacuum leaks basically mean air that is entering the engine where the air flow meter has not had a chance to meter it. Unmetered air, is unexpected air, and as such causes a lean fuel mixture.

So where is unmetered air able to enter on the throttle body?


1. ICV Elbow – These are press fit from factory and loosen over time – There is a limited run of 100 CNC units that we have made to solve for this leak:

CNC ICV Elbow – Fix for ICV elbow vacuum leak E30 M20 engines

2. Elbows to hoses going to brake booster – Stay tuned for a CNC version of this once the CNC ICV elbows are sold through.

Both of the below can be replaced with INA HK08122RS, a dual seal bearing.
3. Top ‘drawn cup’ bearing (OEM is 2 seal)
4. Bottom ‘drawn cup’ bearing (OEM is 1 seal) — This is why you get oil in your TPS, seal is dried up.

5. Evap barb – the barb itself doesn’t leak, but it must either be capped, or there must be no leaks between it and the purge valve that connects to it.

6. Breather hose to valve cover – make sure there are no cracks in the rubber hose, and that the hose clamps are tight.


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