Really Bad Loping Idle

[LordFly]

In the last few days since it started getting colder out, my car has started loping really bad. Not all the time, but maybe half the time it goes to idle. It rev to about 1500, then drop to 0, then repeat. I'm not sure hot it keeps running when the tach hits 0, but it does. Sometimes it'll be fine, and usually after about 15 or 20 seconds the loping will go away. Doesn't matter if the engine is cold, or fully warmed.

Probably related, but I've noticed it the last couple of weeks, when I start it, it'll rev up to almost 2k, then slowly come back down, then stall out. If I restart it, or give it a little gas before it stalls, it'll be fine. Any suggestions?

[LordFly]

Nothing?

[garetth]

Most likely a vac leak switching from open and closed loops. Get some carb cleaner spray around engine bay. What's driving conditions like?

[Skym]

Stalling = TPS not on idle contact (ECU doesn't kick rpm up to stop engine from stalling) or faulty if engine randomly stalls when stopping.

Up (lean) and down (rich) idle can mean there's a faulty o2 sensor (lazy), but engine would run very rich when this happens, popping sound from exhaust.

Unplugging o2 sensor stops this (temporary measure until replace o2 sensors, as GTR has 2x o2 sensors). But it's best to let a tuner do it, as engine could be running lean for some reason (need a wideband to check, which a tuner has or buy one).

Usually both TPS, o2 sensors are checked, replaced if necessary every 30,000-60,000km.

But the up and down idle can also mean there's a intake manifold airleak (intake gaskets have blown which is common on GTR, GTS engines) and the o2 sensor, ECU is making the idle fluctuate up (lean) and down (rich).

Also check that the idle rpm hasn't been raised to compensate. That requires Nissan to help reset it via Consult. or can do it via screw on side of ECU, which is a bit tricky if haven't done it before.

[LordFly]

Hmm, yeah, that would make sense. I could see it being a bad vacuum leak from a blown intake gasket. I'll definitely start there, then move onto the O2 if it's not a gasket.

[LordFly]

So it snowed pretty good here yesterday. Everyone turned into idiots, and it turned my 13 minute commute into a 45 minute parade. By the time I got home and pulled into the garage, the problem had gone away. I drove it 2 more times that night, and once this morning, and still no sign of the problem. I'm confused, but pleased

[caliber676]

Maybe a intermittent misfire or electrical issue.

[Skym]

Thinking about it more, the 1500rpm idle is most likely MAF related (when ECU doesn't see the MAF), but could be the o2 sensor upsetting the MAF.

The colder conditions reduce the heat inside the square part of MAF and on the MAF sensor itself, as has a IAT sensor. That would indicate there might be a dry solder problem inside the square part of the MAF or thermistor problem on the sensor of the MAF in the tube part.

It's worth buying new MAF's. Avoid second hand MAF's if possible (same problems due to age).

Also if the temperatures outside rise the MAF most likely will play up (it's one of the symptoms of a faulty MAF).

Next time it does it (constantly), turn engine off, unplug both MAF's and start engine to see if it stops. If it does stop, you have found the cause. Stock ECU can start, run without the MAF's, but engages a rev limiter around 2500-3000rpm and sets off a MAF error code on the ECU.

You'll need to remove the negative battery cable (with engine off and key out of ignition barrell) and press the brake pedal few times to take any charge out of the system. Then refit negative battery cable to reset ECU (clear MAF error codes). That's after you plug the MAF's back in.

[RSTuning]

maf, vacuum leak,

unplug maf and start car, it wont rev past 2500rpm due to the maf being unplugged but this way you can eliminate the maf. use electronics cleaner to wash it down if problem persists with it plugged in replace.



^^^^ what he said.

[LordFly]

Awesome, I'll try that! But it's been good for about a week now :/ Not complaining, but it makes it hard to trouble shoot.