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Rough idle (cycling) when cold

Starts right up and runs fine when it is warmed up. Just got it back from my ‘car talk’ mechanics and they haven’t been able to diagnose the problem.

Is that all we get? No make, model, mileage, engine, description of the symptoms, prior history?

Than all I can offer is

2000 Infiniti I30. 3 liter with 140,000 miles. They cleaned the throttle plate.

If you mean the idle cycles up and down, say, 1000 rpm over a second or two when cold, I’ve only seen this once, on a Ford, and a new fuel pump fixed it.

I hadn’t noticed the rpm’s - .sounds like up and down a few hundred rpm. It takes about 5 minutes before it runs OK when I put it in gear.

Other suspects: idle air control valve:

Picture 2

and engine temperature sensor(s).

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I too would suspect the temp sensor based on the little information we have.

Thanks to both of you. I will check into both of those fixes.

Thanks. I will check into replacing that or both.

I had a problem gm, it would surge 400 rpm at idle and while driving every 30 seconds or so, my mechanic said disconnect the battery and rest the brains. It worked. Some cars do not like their brains reset, but it might be worth asking the dealer if there is a software upgrade available.

I had a similar symptom on my Corolla, turned out to be the idle air control valve. I’ve had vacuum leaks cause that symptom on my truck though. Those are the two places I’d look first if it were my car. Beyond the other ideas above, a faulty throttle position sensor could be another – less likely – cause. My guess is that if this car possesses an idle air control valve, that’s the problem. That’s what that part mainly does, control the idle speed during warm up. It has no effect once the engine has reached operating temperature. So the symptoms are mostly consistent with that part being the problem. The main problem w/this theory is that usually a shop would clean and check the operation of the idle air control valve as part of a throttle body service. So OP should ask if that was done or not.

I’ve scheduled to have the idle air control valve replaced on Wednesday. Will let everybody know if that did the trick.

I had already tried that to no avail. I’ve scheduled to have the idle air control valve replaced on Wednesday. Will let everybody know if that did the trick.

Sorry for not getting back to folks sooner since I was out of town. Replacing the idle control valve and sensor failed to cure the problem. Thinking now that a mass air sensor? Will probably wait until after the holidays to try the next logical fix.

If your a little handy you can try cleaning it using maf cleaner.

I got around to replacing the mass air flow sensor last week and had it reprogrammed. They did not indicate any computer issues. I’m still having a problem with a rough idle when the engine is cold. I think I’ve run out of ideas so I plan to let it go and hopefully a service engine light with a code to diagnose will pop up some day. Any other thoughts out there? Thanks.

not necessarily my Nissan experience will help, but upon cleaning a throttle plate (which you mentioned earlier), you are supposed to perform the “idle self-learn” procedure

for my Pathfinder, the procedure was:

  • start from warm engine
  • shut down and disconnect MAF
  • start engine and let run for ~5 seconds, until you get CEL
  • stop, reconnect MAF
  • turn ignition on, do not start, clear MAF code, turn off
  • start engine and let it idle for 20+ minutes, do not touch the gas pedal
  • drive as usual after that

you can find more info at or relevant infinity forums (if any)

What does your intake manifold vacuum measure, cold vs warm engine?

Don’t know about the vacuum. I made an appointment for the Infiniti dealer to check it out on Tuesday. I’ll let you know the verdict. (I’m about ready to just put a block heater in it like we did for my years in the USAF up in Minot, ND!)

Well, now the Infiniti mechanics have spent a few days scratching their heads. They did the “self-learn” on the IAC and reprogrammed the MAS again. Now I’ve got the car back to see if I can locate a remanufactured ECM - the next best guess in the progression. Not about to plunk down for a new ECM through Infiniti - that would be almost what I paid for the car! Still don’t plan to shoot it, but the block heater may still be on the table if this doesn’t work! Any other ideas while I move forward with this next step?