This 1998 Maxima, auto trans, with 170K miles performs flawlessly except periodically on cold starts when ambient temperature is below 60-65F. Above the 60-65 temp, turn the key and it starts with rpm steady at 1200 or so and as engine warms up rpm decreases. Below 60-65, sometimes rpm needle swings up maybe 1500 then down very quickly and without intervention, the engine stalls. Intervention is to tap the gas (really air) pedal. This usually works, but sometimes need to try to start a second time and give it some gas to have rpm at 1200 or so and steady. No codes. Years ago, Nissan dealer checked it out and gave me a service bulletin that broken wires in the harness to the ECM need to be investigated. They checked Idle Air Control Valve and cleaned it. Did not solve the problem. In 2024 I installed new IACV [WVE 2H1133 from Rock Auto] and it seemed to help in 24/25 winter; but problem exists to lesser extent. In the course of changing out the IACV I did some ohm checks, continuity checks, and ground fault checks as outlined in the shop manual. I did not disconnect wires from the ECM, to do these checks, as could introduce other problems. Did not find any evidence of broken wire, or ground fault. The ohms across some of the terminals of the new IACV are different than the shop manual says is normal. As of this writing, forget how the ohm readings across the terminal of the old IACV compared to shop manual normal ranges. Key point is that the unsteady cold start rpm is only when ambient temperature is below 60 F and with a love tap to the gas the rpm may do a dip, but returns to the expected 1200 and is steady. Thanks ahead of time for your response(s).

 

check the engine coolant temperature sensor and it's connector as well as any small coolant leaks. a sensor reading off or too much air in the cooling system can really throw the idle off. I've seen it so bad that it can flood the engine making it hard to restart. sometimes the factory hose clamps may only leak as the engine cools off letting in air.

 

HI uptownsamcy,
Thanks, suggestion makes sense, but a question before my attempt to access the coolant temp sensor in hard place to reach. If the coolant temperature indication on the dashboard is behaving normally, is there reason to suspect that the sensor is not working? The needle on the gauge on dash is a bit below the horizontal after warming up. No sign of sensor misbehaving. BTW, I checked the easier to access inlet air temp sensor and it checks out OK per shop manual procedure.. As of now, will wait until cooler weather to reevaluate problem in light of doing new IACV summer of 24. This made a big improvement. This would be a perfect FL car, instead of NH where we salt roads and have 6 months of winter.

 

when you have air in the system it won't really affect the temperature gauge unless the coolant gets real low, but it will throw off the air fuel ratio.

I have an 02 and a few years ago I could already see the factory hose clamps were losing tension. I had no leaks while running but would see drops on the floor after the engine cooled off. I ended up changing every hose clamp.