Unstable RPM with PFC

[510fever]

Just wondering how stable eveyone's RPM is as displayed using apexi PFC?

Mine varies +- 50 RPM at least. I have a lumpy idle and assumed it was instantaneous rpm fluctuations at first, but have decided that is not the case since it occurs at a steady cruise RPM of 3000. While cruising at a steady state, RPM constantly varies between 3000 and 3100, etc.

Is this a common occurance with pfc or do I have a sensor/wiring issue?

Thanks

[Wingnut]

I haven't seen a car yet that holds a pure steady idle. 100RPM drift is nothing.

[Dragon Humper]

Mine hunts at idle (non-stock cams) but it's a timing issue, the timing wanders from 20* down to sometimes 5* BTDC when the car is warm (might be the CAS). At a steady cruise of 3000rpm though she is rock steady. D-jetro and no O2 sensors.


Jon.

[MikeM@Ztune]

510fever, +/- 50RPM is pretty normal for any early 90s Nissan engine. Idle is controlled by the Idle Air Control Valve (IACV), and they tend to get sticky and slow when old. If your idle doesn't hunt too badly and your car doesn't stall when you push in the clutch, then I wouldn't worry about it!

Dragon Humper, it sounds like you need a new IACV...I doubt it's your CAS, but both can be tested to confirm. If your IACV can't hold idle steady, then timing will bounce all over while you're in active timing mode.

[tokes]

I don't know how 3 people missed it, but he's talking about his RPM's fluctuating around when he's cruising along in gear @ 3000 RPM's

[Skym]

Check for airleak behind AFM.

[510fever]

Thanks Tokes, you are correct, the engine speed as displayed on the PFC changes 100 rpm no matter what steady state speed. I will check for leaks, but i dont think that is the cause since i dont feel any shudder at cruise.

I basically am wondering if this is common to all PFCs or if I have a sensor/wiring issue.

From an early reply sounds like the latter since the poster has rock steady rpm at cruise. Would any one else care to confirm this?


On another note, I do believe I have some form of idle issue. not only is it SUPER lumpy, but PFC wont control the speed lower than 950 rpm. I can set idle to 800 and it still likes to range from 900 to 1000. It could be a leak, bad IACV, or the throttles out of equal tune, and I would love to hear some ways to cross each possiblity off the list. BUT, the RPM at high speed issue cannot be caused by this (so I believe).

Thanks for the input everyone

[510fever]

PS I have turned Idle Ignition Control off

[Skym]

The only other things I can think of at cruise conditions is throttle enrichment settings (increase fuel) are wrong or 02 sensor, TPS problems (TPS is related to throttle enrichment settings). RPM's rising can be lean A/F ratio and falling a rich A/F ratio. Check TPS voltage at TPS plug. Both sensors can make ECU run engine richer or leaner and make engine miss at idle. TPS fails earlier if you thrash car (racetrack, etc).

Try disconnecting o2 sensors (disables o2 sensor feedback) and see if problem goes away. My car would jump around rpm wise, splutter, pop flames with o2 sensor connected at idle, cruise conditions and when disconnected, idled smooth and no popping, etc at cruise conditions. That's with factory ECU, but should work the same with PowerFC.