Revs dip on light throttle, Otherwise perfect! Options

[gturner008]

A little bit of experience and wisdom needed.

I’m new to 914 - so don’t know if this is normal for the 2.0 1976 engine.

Engine runs perfectly. Great starter. Smooth and easily revs. Very happy.

But I noticed when it’s ticking over - and I gently rest my foot on the throttle - and apply a tiny bit of pressure, the revs dip - and it almost wants to die.

Apply more pressure or quick pressure, and it picks up perfectly.

Any ideas on what might causing this? Or is it a characteristic of this engine and injection system?

Very grateful for any thoughts. Thanks. Gary

[BillC]

A little bit of experience and wisdom needed.

I’m new to 914 - so don’t know if this is normal for the 2.0 1976 engine.

Engine runs perfectly. Great starter. Smooth and easily revs. Very happy.

But I noticed when it’s ticking over - and I gently rest my foot on the throttle - and apply a tiny bit of pressure, the revs dip - and it almost wants to die.

Apply more pressure or quick pressure, and it picks up perfectly.

Any ideas on what might causing this? Or is it a characteristic of this engine and injection system?

Very grateful for any thoughts. Thanks. Gary

Sounds like one of the tracks in the throttle position sensor (the one for the "accelerator pump" function) might be worn away, in the just-off-idle area. IIRC, 914Rubber has replacement board kits available. Might be worth taking a look at.

I did mine a while ago, and it should only take a couple of hours to do, from start to finish, including recalibrating the TPS.

[ctc911ctc]

A little bit of experience and wisdom needed.

I’m new to 914 - so don’t know if this is normal for the 2.0 1976 engine.

Engine runs perfectly. Great starter. Smooth and easily revs. Very happy.

But I noticed when it’s ticking over - and I gently rest my foot on the throttle - and apply a tiny bit of pressure, the revs dip - and it almost wants to die.

Apply more pressure or quick pressure, and it picks up perfectly.

Any ideas on what might causing this? Or is it a characteristic of this engine and injection system?

Very grateful for any thoughts. Thanks. Gary

Sounds like one of the tracks in the throttle position sensor (the one for the "accelerator pump" function) might be worn away, in the just-off-idle area. IIRC, 914Rubber has replacement board kits available. Might be worth taking a look at.

I did mine a while ago, and it should only take a couple of hours to do, from start to finish, including recalibrating the TPS.

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[gturner008]

Thank so much. Very helpful.

What do you think about the idea of removing the TPS and spraying in cleaner? Could this work? Is am I going to cause more harm than good?

[Bartlett 914]

The cover comes off easily. You can clean the contacts and make an assessment if the traces are damaged. There is an adjustment procedure for the TPS. I don't have it handy but search and you will find it.

[gturner008]

Eventful day.

Took off the TPS, got inside. Photo attached. It does not look to me to be the issue. Of course it still might - but contacts look pretty decent. Only 40k miles from new.

I rechecked all vacuum lines. All good.

Car runs like a dream. So smooth and balanced. The only tiny issue is on that featherlight throttle - revs dip.

If I put normal throttle pressure, it’s fine. No hesitation or anything.

I think I’ll let it pass, and go enjoy the car. Unless anyone has another thought or advice. Welcome any at all.

Thanks. Gary

[PlaysWithCars]

The trace for the "accelerator pump" isn't your problem. It has the same function as an accelerator pump on a carburetor only instead of moving a diaphragm to squeeze extra fuel into the air stream, it cycles the injectors open and closed. It only works to add extra fuel as the throttle is being opened, not to enrich it at a fixed throttle position.

If I recall correctly from my '74 2.0, the other traces on the board are used to sense throttle position and inform the fuel injection ECU so it can supply the right amount of fuel based on throttle position and load (measured by the manifold pressure sensor). Someone else suggested checking the adjustment of the throttle position sensor. I think that is where I would start. My guess is that it isn't changing resistance when you move the throttle very slightly off of idle. The result is extra air entering w/o the computer knowing to add extra fuel.

[gturner008]

Bingo!

I scribed the position at the start, before removing.

It had never been off the car before. After cleaning, I then put it back precisely in the same position. No joy. Same issue.

I then took your excellent advice, and moved it clockwise very slightly, and now I don’t get an hesitation whatsoever.

Big thank you all for your expert advice. Such a great and friendly forum.

So much appreciated. Gary

[gturner008]

Update. I now get the slight hesitation at 1500 rpm. Seems I need one of those new boards. Must have an issue in the track that’s moved.

G