buellrunner

Is a slight (and I mean +- 50 to 80rpm max) fluctuation of RPM normal for 964's when nice and hot?

My mechanic fixed a stumbling idle issue I had developed after having some work done on my car, and I dont remember if the motor previously fluctuated RPM's at all?

sits at around 750rpm....then when sitting in neutral will ever so slightly bounce up and down just a bit....normal?? Do your 964's do this?

Cheers!

springer3

Mine seems to stay pretty stable, but it is normal for controls to "hunt" just a little bit. It will do no harm if you want to live with it. Cleaning the ISV might make idle more stable.

buellrunner

Thanks Springer,

When you say "pretty stable", does that mean that there is no fluctuation in RPM at all?

Cheers,

TR6

Mine sometimes fluctuates about 50rpm +/- if I remember correctly. No big deal. It usually settles down to a steady rpm pretty quickly. It may have something to do with electrical load, etc on the engine (oil cooler fan, AC, etc).

edit: I also have a light weight flywheel which may contribute to idle fluctuation.

911URGE

I watched my idle while running the scantool setup and watched mine fluctuate about +/-20 rpms. Fluctuation was not noticable on the tach and I could not sense it.

I believe factory spec on idle is 880 rpms +/- 40

buellrunner

hmmm..

Well, my story goes as follows:
I had my clutch replaced, and when I got it back the rpm's were hunting up and down VERY noticeably. I brought the car back to my mechanic (who is quite well known for quality Pcar work), and by fluke it seemed that my Airflow sensor (the silver box) had failed at the same time as the clutch job being done. So, he put a new one in, no cost. Seemed to be running great after that.

I cant remember though, if there was any tach movement at all at idle. I don't think there was...but now the needle will move up and then down +-80rpm every 10 seconds or so when the motors hot. Doesnt do it when cold, and starts beautifully when cold with no idle hunting or jumping.

This is why I'm asking what others are seeing in their 964 RPM gauges when hot...

Regards,

TR6

I think my fluctuation is when hot also which is why I suspected the electrical load from the oil cooler fan might be affecting/causing it. Just speculation though. But mine doesn't do it continuously. It seems to settle out after a bit.

buellrunner

Just spoke to my mechanic...said a tiny bit of RPM fluctuation is normal...not to worry about it. Going to get a second opinion from a great mechanic tomorrow afternoon. Ill let you know what comes of it.

What amazes me is that I took my car in for a clutch, and the Air Flow Meter ended up going bad at some point during the job. Wierd. Symptoms were a constantly hunting idle when hot. up and down between 800 and 1000rpm...would never settle. New Air Flow Meter fixed the problem. Mechanic said it was Murphy's law, pure coincidence.

Not too happy about it. But I have a new one in there. Those parts are never supposed to fail....

Anyway, just venting...

MisterRisky

is yours a tip or manual?

DarrylH

Like Stephen, watching the idle with a hammer, at least in my car, it fluctuates 880-920-880-840-880 and repeat. This small variation can be heard, but not seen on the tach. The variations are greater if a system idle adaptation is needed, e.g. after disconnecting the battery. Might be worth connecting a hammer to yours, just to see what it's doing, and maybe to do an idle adaptation to see if it helps.

buellrunner

Its a manual...

I can hear the fluctuations...but I can also see the tack move up and down ever so slightly. Ill see what my mechanic says tomorrow....

Thanks!

springer3

I would have said "rock stable" if that were the case. The tach needle does not move that I can notice, but I can hear the engine note change ever so slightly. The O2 sensor is essentially bi-stable, so the engine controls are designed to cycle from rich to lean as the O2 cycles from "it's too rich" to "it's too lean". I have always assumed the note change in the engine was a lambda control cycle, and that lets me know the O2 sensor is fine and the engine controls are working. I go for emissions check this month, so I will soon know if all is well back there.

ChaseN

My car does the same as springer3's. At idle, I can't actually see the tach needle move, but I can hear the engine fluctuating very slightly.

TEN DOLLAR

My 964 "hunts" when it's hot too. Not much - only 50 rpm either side of 750 but it can be heard. The tacho and oil press gauge show the hunting too. It's a small issue but it really annoys me. I've replaced my coils, dist caps and rotors, cleaned the entire induction system and I still can't shift it. I did read in a manual the other day that a sticky resonance valve in the induction system, can cause an uneven idle, if it doesn't close fully. My car does have a surge in engine noise at 5500 rpm - a bit like the clutch has suddenly slipped. I know this valve is supposed to open at 5500rpm. So this valve could well be sticky and is my next line of investigation. Just a thought.

Cheers TD.

Blown Away

I would suggest that a good clean of all those little sprung plugs visible around the top of the engine would be a good move first of all. Wet and Dry paper and a little WD40 penetrating oil seemed to solve mine hunting.

If that doesn't solve it, it could be a sensor problem or other connector problem.

If your engine /top end is fairly worn you could be getting oil in the combustion chambers which may also affect the idle.