Think positive, the re-learning on the IAC and re-programming the MAF sensor may have fixed it. If not, rough idling when cold suggests the mixture is too lean. Some combo of too much air nor not enough gasoline entering the cylinders. That could be caused by a vacuum leak, air induction system leak, low fuel pressure, faulty engine coolant or intake ambient air temp sensors, clogged injectors etc.
We finally to got to the bottom of this problem after these many weeks:
"After repairing my buddy’s 2000 Max for the exact same problem, I would be willing to bet on the o-ring gasket for the plastic upper intake manifold. BTW, it also had the new MAF, ECU reprogram and six new coils that helped but did not totally fix the issue.
An air leak is created by the old brittle gasket where the plastic upper manifold meets the aluminum lower manifold. Gets better when the engine is warmed up.
The parts man at my dealer has seen several of these, and recommended this as a fix.The updated part number should be in the database at your dealer. Sorry I don’t have it in front of me, but the dealer should have it."
Thanks to everyone for their help in troubleshooting. I have passed on the word to my ‘car talk’ and the Infiniti mechanics.
L J Pressman
OP … your post above is a little unclear. Is it solved now? Was it in fact caused by a vacuum leak due to a faulty upper intake manifold gasket?
Yes, that O-ring was the problem. I have not had any problems since.
Glad to hear you are back to a smooth running engine. Good for you for sticking with it.
A new problem just cropped up. The transmission has started to whine a little when I back up. It quits when I’m in any of the forward gears. Any ideas as to whether a simple fix or am I looking at overhauling the transmission? It is a 2000 Infiniti I-30 with 142,000 miles. Since it’s got quite a few years, if it’s an expensive fix I may need to move on.
Check the transmission fluid level.
Your 18 year old car with 140,000 mile on it just started to whine a little in reverse? That could go on for 10 years or more without causing any problems.
First thing I did was to check the transmission fluid (had it and filter changed about 120,000 miles). I also added a transmission additive when it started to whine. I’m optimistic to hear that it could hang in there for a long time yet.
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Sorry that I’m a bit late with this update. I knew I needed to replace my rear disc pads, which I did a couple of weeks after this post. Lo and behold, the whining sound went away. It turned out that the whine was the metal clip on one of the pads scratching against the rotor - but only when I was going in reverse. So happy to feel even more confident now about my transmission! On most of my other cars, those reminders of a low disc pad really made a loud grinding noise to get you in gear to replace the pads and rotors.
Glad you got those whining brakes diagnosed & fixed w/no transmission problems. Good for you. Thanks for the update.