Idle adjustment on Mahindra?

[brazosdog]

I have a very obvious high idle set screw, but there is nothing for the low idle anywhere. So, I guess this is internal somehow? It’s a 3505DI and the pump says Mico Bosch 25 and a lot of other numbers on the tag.

I’d like to kick the idle up to spec around 750 as it’s a hair low just no screw on the outside to set that.

 

[brazosdog]

On the Mahindra 3505DI, the 3-cylinder engine features a mechanical Bosch-Mico inline injection pump. Because you only see the high idle screw externally, your pump is equipped with a mechanical RSV or RSV-style governor attached to its rear. [1, 2]
On this specific Mahindra setup, the low idle is not adjusted by stopping the external accelerator lever. Instead, it is controlled internally by an anti-surge/buffer spring located at the back of the governor. [1, 2]

Where to Find the Low Idle Screw

1. Walk to the side of the engine where the injection pump is mounted. [1]
2. Look at the very back wall of the pump housing (the rear-facing flat metal cover pointing toward the tractor's driver's seat/clutch housing).
3. Projecting straight out of the upper middle portion of this back plate, you will see a small threaded stud with a screwdriver slot and a locking hex nut. It is often covered by a domed metal cap nut or a plastic thread protector to prevent tampering.

Step-by-Step Adjustment Procedure

1. Warm up the engine: Run your Mahindra 3505DI until it reaches its normal operating temperature. [1]
2. Remove the cover cap: Spin off the protective dome cap covering the rear stud if one is present.
3. Loosen the locknut: Use a small open-ended wrench (typically 10mm) to break loose the jam nut holding the threaded stud in place. Keep the screw from turning with a flathead screwdriver while you break the nut loose.
4. Adjust the low idle:
   • To increase idle speed: Turn the inner screwdriver slot clockwise (inwards). This increases the internal spring pressure against the internal governor linkage, raising your base RPM.
   • To decrease idle speed: Turn the inner screwdriver slot counter-clockwise (outwards). [1, 2, 3]
5. Set the position: Turn the screw in small 1/4-turn increments. For this Mahindra engine, aim for a smooth baseline low idle between 650 and 700 RPM. [1]
6. Lock it down: Hold the flathead screwdriver completely steady so the inner screw does not migrate, and securely tighten the 10mm jam nut down against the pump housing body.

A Critical Warning Note
Do not confuse this idle stud with the larger fuel-delivery or torque-control screw lower down on the rear backplate. The low-idle screw is the smaller, thinner stud located higher up on the rear governor face.
Is your engine idling too low and stalling, or are you adjusting it because the engine is surging (revving up and down unevenly)? If it is surging, adjusting this buffer screw will resolve the unstable engine speed.