Engine hunts at idle

[Rich_NYS]

The original paperwork that came with my car states it's normal for it to hunt....ever hear that one?

[Horsebox]

The original paperwork that came with my car states it's normal for it to hunt....ever hear that one?

Never heard that before but interesting! Who wrote that, DMC?

I think I remember from the Pennebaker documentary that they were moving cars about on the boat and one of them sounded as if it was hunting.

Maybe first generation idlespeed control really was running at its limits even 36 years ago.

[opethmike]

No, it is not normal for them to hunt. I had the factory K-Jet system on my car for the first five years of my ownership, and had no issues with hunting.

[David T]

Hunting or surging is a relative term. By the specs the idle is 775 RPM + - 50 so even if it fluctuates from 725 to 825 it is still within tolerance. A well tuned motor shouldn't fluctuate that much. One thing you will notice is the frequency valve. It makes a lot of noise and it's pitch changes as the RPM's change which makes the hunting more noticeable.

[airfireman1]

I think it is running too rich now because it has no vacuum leak. It certainly is more responsive now, but it hunts at idle between 600 and 1000 rpm. I do have bad hearing but I don't think I can hear the frequency valve buzzing. Would I be able to feel it if I put my hand on it? It idled rock steady with the vacuum line not connected, ( open to atmosphere ).

[opethmike]

Yes, you should feel the valve buzz if you put your hand on it.

[airfireman1]

Finally getting some time took look at my car. I have replaced all the vacuum lines that I can get to but not the ones hidden under the intake manifold. I can't see how you can change them without taking the manifold off. I can definitely say that I cannot feel the frequency valve buzzing. Engine is at operating temp.
At the moment it can idle nicely at 750 and other times it will idle between 500 and 1100 rpm. So my question is what causes the frequency valve to operate and what would make it fail?. I cannot get a decent dwell reading, It just pegs out to one end of the scale. I have connected it to the Orange wire at the bulk head as I don't have the diagnostic wire at the back of the engine.
I know that the car has never had the O2 sensor changed and it has never had a Cat converter fitted as it is Euro spec.
It has only recently had new injector seals and fuel pump and filter. I have had to unplug the cold start injector because when the engine is warmed up then shut off it will flood the engine when re starting.
When the car is at operating temp it drive very well, its just the crappy idle that annoys me.
Any input would be appreciated.
Cheers

[Bitsyncmaster]

The most common cause of the FV not working is someone plugged the wrong relay into the lambda relay position. That relay position is wired differently for some unknown reason.

[airfireman1]

OK will check that in the morning,
Thanks again

[David T]

Bunch of "common" reasons the frequency valve stops buzzing.
Wrong or bad Lambda relay (it is different from all of the others so sometimes they get switched around and the wrong one winds up in the Lambda spot)
One of the connector terminals in the block "backed out" and is not making contact with the relay
The connector plug on the frequency valve has some corrosion. Plug and unplug it a couple of times
Someone disconnected the ground wire to the frequency valve. It has to be connected to ground on the engine.

Next bunch of problems with the Lambda system:
O2 sensor missing, disconnected, contaminated, or just old
Mixture screw WAY off/plug missing
Vacuum leaks.
Bad/misadjusted micro switches on throttle spool

The Lambda system can not work correctly if the motor is not in "good tune". All of the cylinders must be balanced and operating as equally as you can get them to for the Lambda system to function correctly. The mixture screw is the LAST thing you touch after you get everything else working good.