I've got a 98 I30 with 162k miles on it, I've recently had the transmission rebuilt due to a slipped overdrive band. I've been having some odd problems lately... It seems like it's idling way too low when in gear, but in park and neutral, it stays about 1000-1100 RPM. Lately, when I first put it in reverse, if I don't let it warm up first, it will occasionally drop below 500RPM and sometimes just die. The other thing it will do, if left undriven for several hours is, after starting up and going into drive, I find that as I slow down to a stop, the RPMs drop below 500, sometimes to 300 and it feels like its going to stall, but usually in a second or two it will correct itself, the RPMs jumping back up to 500-600RPM, almost as if it had a late downshift or something, also sometimes the shifts feel rough, sometimes they feel fine... The car isn't throwing any codes, so I don't know where to start, the only thing I can think of that needs replacement is the belts, anyone had any similar experiences they can help with?

 

Whoa 1100-1000 rpm is really high for an idle. mine is set around 700-800 maybe even a little lower. it sounds like u have a vaccum leak because when the car is dieing you usually are applying the brakes correct?

 

I have had the same problem you described when coming to a stop in both my '99 i30 and old '95 maxima...i asked around and i dont think there's a way to fix it. It happens when it's cold out, when you're coming to a stop, right before you actually stop the RPMs go down to like 3-500 and and you can feel a little vibration, then they go back up to idle. I dont think it's the transmission, b/c mine's in excellent shape and gets its fluid changed regularly at infiniti...it's also not a misfire b/c i had that a few months back and had all the coils changed. The car never actually dies, but the RPMs go pretty low. Anyone know what could be wrong?

 

Maybe the IACV (idle air control valve)

If there is another VQ in the area, you might swap them out to see if thats the problem.

 

That may be right, because when it is dying, it's when I'm applying the brakes, but only in reverse, only if I don't let it warm up, and it's sudden, there is no drop in rpms, it's just a sudden cutoff.

the 1100-1000 rpm idle only occurs in park and neutral before the car is warmed up... maybe it's the IACV, I have another entire upper manifold sitting at home, egr, iacv, tb and all... I may cannibalize it for parts soon.

 

try that and see what happens. i dont know exactly what is done to find vaccum leaks so im sure another fellow orger can help ya out. but from what the symoptoms are it sounds like a leak of some sort. just for kicks try to run some seafoam through ur motor using the brake booster hose and see if that helps any.

 

If you had a vacuum leak, you would more than likely know as it loud as hell (unless you are extremely oblivious).

Anyways, clean your throttle body and idle air control valve, then adjust the base idle to factory specs in the 4th gen stickies, and go from there.