Hey guys,

First time owner of a 91 Maxima. Heres whats going on..

1) when I put the car in drive, it hesitates to catch at least when its col, preventing me from driving .. also makes a loud humming noise

2) the rpms will also fluctuate down when I am stopped .. sometimes close to the point of stalling for going too low. It will fix itself, then the rpms will go higher than normal. When im driving it also will speed or slow down slightly on its own

3) I put the car in Drive at a parking lot and sat idle to make sure I wouldnt stall, and my engine temp shot all the way up. Checked coolant. Full. Oil was clear.

I drove it home with the heat on, the car stayed cool, the rpm fluctuations stopped, and I stopped nearly stalling at lights

Friend says he thinks its thermostat, another friend thinks its a worn belt (because of Drive not catching right away. Thoughts?

Thanks so much in advance for your help!

 

For your idling problem, you may want to check/clean the TPS (Throttle Position Sensor).

The over heating could be many things. the thermostat is always possible. When the temp gauge shot up, was the engine coolant coming out as in boiling over? If it wasn't, the ECTS (Engine Coolant Temperature Sensor) could be reporting the wrong temperature.

 

1 - put it in 2 and see if the car will move...if yes then you have a bad shifter bushing. if not then check your ATF fluid to make sure you're at the proper level. if the fluid is ok then you better start saving up for a rebuild.

2 - this points to a lot of different possible issues. TPS, O2, MAF, your transmission slipping, carbon build up, spark plugs/spark plug wires, cap/rotor, plugged up fuel filter, etc etc...the list goes on.

3 - did you see steam coming out of the coolant tank..was the car actually over heating or was the needle pegged? t-stat, water pump, radiator, temp sensor(s), fan motors, are all possible culprits.

 

For your overheating issue it wouldn't hurt to just change the thermostat being they're pretty inexpensive i'd also in the meantime try making sure you don't have an air lock by removing the 8mm bleeder screw at the back right side of the intake manifold and warm the car up to operating temp. and check to see if your coolant is bubbling out or not and for your idle fluctuations you could start by checking all your vacume lines for cracks. Old rubber tends to crack and deteriorate especially if none have been changed with the car being over 20 years old. If your fans aren't coming on then i'd also look into changing the coolant temp. sensor which is also pretty inexpensive.

 

Make sure your radiator isn't sludged up. If it is, good chance that the heater core is sludged. That will also keep an air "bubble" in the system and cause some coolant flow fluctuation. I agree w/ what ac max 92 said re: temp sensor and hoses.
If, and this is a big "if", the heater core is causing the air bubble issue, you must remove the entire dashboard assembly and replace the heater core. There's pretty much no way to clean it out without replacing. I've tried power flushing and it didn't work.
So if you also hear an annoying gurgling noise inside the car and can't solve that with using the bleeder screw and power flushing, I'm sorry to say your heater core is clogged. I did the job myself 2 years ago and saved probably $900+. It's a beotch of a job. See my write-up where I posted my pleasant experience!