Mi16 high idle. Throttle body testing?

[davemar 16]

I'm trying to get to the bottom of the high idle I've got on my Mi16 engine (1.9 running normal Motronic ECU). I've checked the throttle switch and that seems to function fine, and the electrics are all good.

 

I'm suspecting the throttle body plates aren't sealing as snuggly as they should when the throttle is shut. Am I right in thinking that at idle the throttle plates should be totally sealed shut and the idle relies on the air passing via the ISCV to get the air supply? So is there an easy way of testing how leaky the plates are?

 

[Tom Fenton 1,541]

There is also a manual bypass with an adjuster screw. If you have checked everything else then you can adjust on that.

Refurbishing the mi throttle body isn’t hard I’ve done a few. The bushes the spindles run in wear out. 

[davemar 16]

I gave it a good clean up recently when giving the engine bay a deep-clean. So clearing the muck out might have knocked the bypass adjustment out a bit. The lack of dirt might also be letting a bit more air through now too. I'll take it off and have a closer look.

 

[davemar 16]

I gave the bypass screw a bit of a clean, and when it is now wound all the way in the idle drops to around 1300rpm. Still a little bit high, but not too bad. The spindles feel OK, and there's no unwanted movement in them.

 

 

[petert 586]

Have you verified contacts in the TPS with a multimeter?

[davemar 16]

Yes, two of the pins become connected when the TPS switches.

 

[davemar 16]

I've decide to try and see if there's any leaking from the throttle body. So I took it off the car and taped over the side that mounts to the manifold and sat it on a bench with that side down. I then filled it with water to see if any leaked out of anywhere. I got a bit of a dribble from both of the spindles on the TPS side of the body. Not a major gushing, but just a light dribble. Would this be enough to cause enough of an air leak to upset the idle this much?

 

As for taking the throttle body apart, how do you undo the two screws that hold the throttle plates to the spindles? They seem totally stuck and any blade screwdriver feels like it's going to make of mess of the slots on the screws. 

[davemar 16]

A bit of an old thread, but I though I'd better share what I found.

In the connector on the throttle switch the wire that connects to the ground connection (middle pin IIRC?) had come free, so the switch wasn't pulling the signal to ground. The other two wires that go to the ECU were fine, which is probably why I missed this one.

Now properly connected it now idles properly!