thankumuch

Periodically, my 97 with 78,000 miles will just go flat while trying to accelerate away from a stoplight. There is simply no power being made when pressing on the gas. It continues to idle smoothly, but no amount of accelerator pedal makes the engine rev. Then suddenly it gets power and runs like a champ. Everything is up to date and maintained. What would cause this huge dead flat spot that vanishes as fast as it arrives? Sometimes it's months between incidents. I'm afraid some part is about to fail, but it's not throwing any codes, so what to look for? Thanks in advance.

JvG

Sounds like the throttle position sensor has malfunctioned. Or possibly the maf.

Stay tuned for opinions from other members.

vqmaxman

I am assuming your an automatic and the first question i have is does the car at or from the stop when you accel at Wot launch, it takes off like an cement truck once it's going it is normal. Did you ever watch the rpm gauge when this happens. The gauge stays or slowly builds up with the car speed. This could be an early sign of a torque converter failing. If the tranny fluid is low this can also happen because of it, check the fluid level on the dipstick. The code should be stored in the tcm and the ses light should be on or on it's way. The best bet is get the code scanner and get it checked. The tps sensor can go bad but it would of triggered the ses light on. Let us know what you got post back.

Turbobink

iTrader: (2)

Agreed ...

Also consider replacing the IAT (intake air temperature sensor).

JvG

Turbobink, Im not familiar with how the IAT could cause this problem. What' the operating theory behind this?

thankumuch

Yes, the 97 is an automatic tranny.The tranny fluid is up to spec. Once the condition clears, the normal stellar performance is back. My guess was some kind of sensor that controls air, fuel, temp, etc... The interesting thing is that idles fine and smooth during these episodes, doesn't die, it just does not respond to throttle input, then poof, it's back and running normal. Thanks so far for ideas. PS, Would there be some clue in the brain, even if it's not throwing a code?

JvG

I'd look up how to test the throttle position sensor.
I had one which was out of adjustment on an old 1970s Volvo I had a long time ago. The symtom was similar.

The ecu responds to information provided by the sensors. If a sensor provides lies instead of good information, the ecu will respond to the lies.

I think that the TPS does not respond at lower rpm, but does at higher rpm.

Turbobink

iTrader: (2)

ECU receives incoming air temperature data from the the air charge temperature sensor (aka intake air temperature sensor).

ECU, with the help of several other sensors in addition to this one, calculates the correct A/F mix based on air temp/density.

In correct air temp. data = incorrect A/F mix = poor acceleration/lack of power.

JvG

Makes sense.

That sensor could be tested with an ohm meter.
Compare the ohm readings to specifications.

Turbobink

iTrader: (2)

It could be tested ... and the OP didn't say anything about engine temps in his initial post ... but the IAT would need to be tested throughout a wide range of air temps to determine where in the temp range the brain-fart, if any, occurs.

I recommended replacement based on the fact that an OE Nissan sensor is only like $23 or $26.