Rough Engine Idle

[DUMPD_VP_CALAIS]

hi my car this morning (engine dead cold) started ok then the idle became erratic. the idle would go down to 500 then up then down again. once or twice it would stall because the revs got so low, but would start up straight away afterwards.

i changed the crank angle sensor couple of weeks ago. The computer diagnostic check showed oxygen sensor faulty...what do check / replace??? any ideas??? i let car run for a bit until the fan came on and the motor got some heat, but still the idle was stupid...For a while now though, after a minute of driving the car when its cold id get the engine warning light come on for about 20seconds - thinking it was the O2 sensor i didnt take much notice cos the car still ran ok with decent mileage...

while the car was idling bad:
-i hit the fuel tank from underneath thinking it might be the pump
-moved around the leads at the coil pack
-moved around the oxy sensor a bit
-checked to see of all injectors working ok
but still it wouldnt idle right.

the engine revs seemed to go up a little then down a little. when i start the car it idles fine for about 3-4 seconds then it starts idling weird

when i drive the car the motor misses pretty badly.

i cleaned out around the IAC valve in the TB a bit, but still not much change. spark plugs changed about 10k kilometres ago.

I dont think its the O2 sensor, or throttle body. I reckon it may be the coil pack because the engine is missing pretty bad. When i got to start it, the revs seem to struggle to go past 500-600, but when i accelerate a little the idle increases (rough as, not smootly)...

 

[beckrey]

i'd be checking ignition leads first
i've had 2 Commodores & on both when they start missing really bad it always seems to be leads or plugs

 

[Chuff]

In the engine wiring loom circuit 452 is a Black wire with a Yellow trace. This wire gets spliced in the loom between the ignition module and the TPS/IAC. The problem may be here, as over the years this splice loses contact and produces an erratic idle which comes and goes for no reason.

The way I found the problem was I moved the engine wiring loom between the ignition module and the engine while the engine was idling, and while doing this the idle increased and decreased dramatically. If you move your engine loom around at this point while the engine is idling, and this makes the idle go up and down, then I'd say the problem is as I have described.

To fix it, follow the loom over the engine to the drivers side you'll find where it attaches to the rest of the loom via a couple of plugs. Unplug the loom from here, remove the throttle body cover and the throttle body, unplug the loom from the TPS, IAC Temp sensor, A/C, 2 grounds etc...

Once you've done all this, take the loom out to the point where the convoluted tubing ends near the ignition module. Remove the convoluted tubing and find the black wire with the yellow trace, then follow this wire till you find the splice. You'll see what looks like shrink wrap at the splicing. Move the shrink wrap and you'll see the splice which is a simple crimp which joins the 2 wires to each other. Redo this and problem solved.

PS: While your there, look for a second splice in the loom. I forgot the wire colors, but it will be wrapped in the same shrink wrap stuff. Might as well redo that one as well while you've got it all apart.

Good luck, and let me know how it goes.

CATCH!

 

[DUMPD_VP_CALAIS]

one of the coil pack things had stopped working. they just just replaced the defective one and replaced my leads. car idles really nicely, must have been on its way out before it **** itself.
thanks beckrey and chuff for your suggestions