Very high idle

[FEP]

My Tech 1 has had a replacement M20 engine with Motronic 1.3.

It wasn't idling vey well and for sure the throttle stop screw was not in its factory position.

I took the throttle body off and cleaned it up. I reset the butterfly to have 0.0015 inch clearance and took the TPS off to clean as best I could. I could not get it open without major butchery so did not do so. The TPS seems to have open circuits across all the pins, wherever the throttle is. Spraying lots of electrical cleaner into it has made no difference.

The ICV seemed to be OK - it buzzes when the ignition is on and the innards rotate when you shake it. I sprayed carb cleaner though it. Should it actually spin when energised? It doesn't.

The resistance across pins 24 and 45 (for the blue sensor temp sensor) at the ECU plug is as it should be.

The boot/pipes do not seem to be leaking anywhere. The AFM is putting out a variable reistance as the flap opens.

When I put it all back together, it idles (hot and cold) at 3,300 rpm. I slipped the TPS connection out of the throttle body and blocked the hole - revs dropped a bit, to about 2,000 rpm

I appreciate that the TPS needs sorting, but why so high? In ideal state, with no throttle pedal, shouldn't the failed TPS have the same effect as a good one?

Given that the TPS appears to be NLA, can anyone tell me if its possible to open and fix without destroying?

If not, is it used parts only or are there viable alternatives?

Thanks

[maggspower]

An engine can only idle in this way if it has the air to do so. You either have an air leak somewhere, or the ICV is passing air at a higher rate than it should.

Also the throttle stop is only to prevent the butterfly from wedging itself in the bore of the throttle body. It should be as close to being completely shut as possible without getting stuck.

[FEP]

Also the throttle stop is only to prevent the butterfly from wedging itself in the bore of the throttle body. It should be as close to being completely shut as possible without getting stuck.

That's not quite what it says on the Wiki:

"If you think the Throttle Stop has been tampered with, or you have stripped and rebuilt your throttle body, then the closing point can be reset using a 0.0015in feeler gauge between the door and the bore of the throttle body. However, to accurately set the throttle stop requires the services of an exhaust gas analyser."

http://www.e30zone.net/e30zonewiki/index.php/Intake

I suspect my problem may well be with the ICV. How do I test it? What should the inside of my ICV be doing?

[Speedtouch]

Remove it and spray carb/brake cleaner in there.

I would also check your throttle cable and accelerator pedal carefully, as if they are sticking or in the wrong position(s), this could well lead to such a high idle.

[maggspower]

Also the throttle stop is only to prevent the butterfly from wedging itself in the bore of the throttle body. It should be as close to being completely shut as possible without getting stuck.

That's not quite what it says on the Wiki:

"If you think the Throttle Stop has been tampered with, or you have stripped and rebuilt your throttle body, then the closing point can be reset using a 0.0015in feeler gauge between the door and the bore of the throttle body. However, to accurately set the throttle stop requires the services of an exhaust gas analyser."

http://www.e30zone.net/e30zonewiki/index.php/Intake

I suspect my problem may well be with the ICV. How do I test it? What should the inside of my ICV be doing?

Oh well the wiki must be right then...... although quite how you get a flat feeler gauge to accurately measure the gap between two curved parts with the same radius is beyond me. And how will a gas analyser know when the throttle butterfly is correctly positioned, when the ICV is constantly adjusting its aperture to hold the idle steady.

ICVs rarely go wrong but can benefit from a clean.

[Brianmoooore]

M20 ICV is effectively two electric motors turning in opposite directions. If full power is applied to one and nothing to the other, it will either fully open or fully close, depending on which motor has the power, and switching power to the other motor, will cause the opposite.
By applying different amounts of power to both motors, the ECU can hold it at any position in between.
The throttle stop adjustment is set so that the majority of the air required for the engine to idle passes by the butterfly, and this is added to by the ICV to bring the idle up to the correct level.
Best way I have found to set the throttle stop is to remove the ICV, either block both hoses or plug the ICV itself and replace it (wiring not connected), start the engine, then adjust the stop so that the engine is idling very low and lumplly, almost threatening to tear itself from its rubber mounts. After this, the TPS will need to be checked to ensure it switches immediately the throttle leaves its stop.
All this must be done after ensuring that there are no air leaks into the inlet side of the engine, after the AFM.

[FEP]

Thanks all.

The throttle cable, pedal and linkage are fine.

As I said above, I have already liberally doused the TPS and ICV with cleaner.

I have sprayed carb cleaner all over the inlet side of the engine - no rise in revs.

The ICV buzzes and when energised the innards do change position. Is there a way to more conclusively test its function?

Does anyone know if it is feasible to break open the TPS, fix and glue back together, or if there is an alternative new part as the original is apparently no longer available?

[Speedtouch]

See the Zone wiki guide to cleaning it:

http://www.e30zone.net/e30zonewiki/inde ... ion_Switch

[FEP]

See the Zone wiki guide to cleaning it:

http://www.e30zone.net/e30zonewiki/inde ... ion_Switch

Thanks Speedtouch. I have been following the Wiki, but what happens if having been cleaned as much as possible it still doesn't work?

[Speedtouch]

It sounds as though the problem is related to the TPS, so I would check that out more thoroughly first - perhaps try borrowing another from a fellow Zoner in your area?

[Brianmoooore]

I've just looked back at the OP, and note that it says that the idle is 2000 RPM with the ICV blocked off.
To idle at 2000 RPM the engine needs a sufficient quantity of air to do so, and the first thing to do is to establish where this air is coming from - either past the throttle butterfly or by some other unauthorised point of entry, such as missing blanking caps, perished/loose hoses, failed gaskets, etc.
The above can only happen because of the reasons I've listed. Nothing to do with ICVs, TPSs, or anything electrical.
When you are sure there are no leaks, set the butterfly stop in the way I detailed in my last post, ensuring that the throttle cable isn't partly holding it open.

[BenHar]

I've just looked back at the OP, and note that it says that the idle is 2000 RPM with the ICV blocked off.

Actually it says: "
When I put it all back together, it idles (hot and cold) at 3,300 rpm. I slipped the TPS connection out of the throttle body and blocked the hole - revs dropped a bit, to about 2,000 rpm "

TPS off, not ICV.

I'm not sure what "slipped the TPS connection out of the throttle body" means.

I wonder if the blanking plug under the throttle body is missing?

Ben

[Speedtouch]

I was confused about that bit too!

Certainly, 3,300 rpm idle sounds incredibly high - half way up the rev range of the engine!

Which ECU is fitted? The later 0 261 200 381 ECU was reknowned for blowing diodes in the idle circuit, which may cause such issues...

[FEP]

Sorry - my mistake. I slipped the ICV connection out, not the TPS. Sorry to confuse.

I will do as Brian suggests and set the throttle to a low and lumpy idle with the ICV blanked off. I suspect that maggspower is right and that my setting at 0.0015 inch was just letting way to much air past. Suppose that may have worked better using a rod type feeler gauge.

As regards which ECU, I remember looking into the different ECUs when I upgraded to Motronic 1.3, but offhand I don't remember which I got. I'll check later.

Yes, it would be great to be able to sub in a known working TPS and ICV, but right now I don't know anyone to help. I'm in London N1 if anyone is offering.

[FEP]

Update.

Using Brian's method of setting the throttle valve, the revs never go below 800 - even with the screw backed off till it is no longer touching the stop.

Running the engine with the boot off allowed me to discover the hissing noise indicating that air was going past the bypass down the right hand side of the throttle body - the one that is varied by a screw on the right hand side that is seemingly NEVER mentioned in Bentley or on here.

It appeared to be set at 1/4 turn out from all the way in. If screwed up tight and with the throttle stop right out the engine does stall. From there, I was able to re-set the throttle stop as Brian suggested. I take it that this bypass screw is not relevant to the set up on the M20 and should be shut? Anyone know?

Any way, I was then able to establish that with the TPS and ICV electrical connectors disconnected, the engine idles, blips and runs exactly the same as with either or both connected.

If the TPS is non functioning, should the ICV be always assuming the car is idling or always assuming that the throttle is partially open?

I have now Dremmeled the TPS open - horrible in there! Cleaned up and all seems to work fine. The gasket compound is just drying now to re-seal it.

More later.

[Kane30]

So, that screw on the TB… was it all ok when turned all the way in? I have that same screw, I did a smoke test and it’s leaking through there as it’s not in tight. I’m idling slightly high but don’t want to just tighten it up if it messes with air mixture. Does anybody know?