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Discussion Starter · #1 · (Edited)
Help!!!

My brother took my Nissan into the shop he works at to see what is causing a hesitation in my idle. Basically when idle every 3-5 secs the RPM's will lower to about 500rpms and almost die. I thought this to be my timing, which I got changed with a couple other stuff, timing belt, cam gaskets, tensioner, and water pump (just to make sure everything was running good and so I wouldn't have to pay extra labour later if it did break down). But that didn't fix my hesitation. When I accellerate quickly and time my shifting at about 5-6k rpm, there is no hesitation and no power loss. But if im just idling at a stop light, then that's when the rpm's drop.

So back to my story, my brother took it in to hook up to the computers, and they couldn't get a positive reading. He said they got no reading at all. Is this because its an older car? So they went to the ECM and up pop up all these trouble codes. Although I don't know if they are suppose to pop up at this point or not? They didn't know about the different MODES that they have to set to get MODE III for Self Diagnositcs. So, these are all the codes that pop up, (just to let you know, there are no engine lights on, nothing to show that there is something else wrong with the car other than the hesitation);

14 Car Speed Sensor
23 Idle Switch
24 Netural Switch
31 A/C
41 Fuel temp sensor

So before I go outta my mind at what I think will be a major repair service. Please anyone out there, help me, let me know if you ran into this, or if you know off hand that newer diagnosis computers can't read an older Nissan, and hopefully they read the trouble codes wrong. I'm anxiously waiting.

Don
 

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ZPOOLNZ
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Did you get the codes through the self diagnosis in the car? Fix code 23, check the MAF, replace the fuel filter and with all that you should be good.
 

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Discussion Starter · #3 ·
JAMESZ said:
Did you get the codes through the self diagnosis in the car? Fix code 23, check the MAF, replace the fuel filter and with all that you should be good.
Well, I wasn't there, and when I printed out the trouble codes off the net there were seperate modes you have to change it to self diagnostics mode. Since they didn't do the procedures to change the mode, I don't know how they got the trouble codes and if it was even in the right setting.

I was thinking it might be the MAF sensor, another mechanic suggested either the MAP sensor or the O2 Sensor. Before I spend a chuck load of money, I want to make sure it'll fix the problem and im not replacing anything that doesn't need replacing.

Eventually I know I want to swap out all older parts just to make sure it'll last another 10yrs. But right now im concerned about making it work.
 

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The only code I see in the above that would affect how the car runs at idle, is the idle switch. The speed sensor might, but I think thats more in the newer vehicles. The fuel temp sensor only affects the engine on startup on a warm day or if vaporlock might be present. Neutral switch? I must assume you have an automatic.

I'l put it like this, if the MAF was not working properly, you would not be able to rev past 2000 rpm. So you can pretty much stop worrying about that.
The idle speed switch is the little black box on the driver side of the TB. It's either bad or likely unplugged, or the wiring is bad. Check that first, it's probably the cause of your problem.
 

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ZPOOLNZ
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♣Zen31ZR♣ said:
I'l put it like this, if the MAF was not working properly, you would not be able to rev past 2000 rpm. So you can pretty much stop worrying about that.
You can rev the car past 2000 if the MAF is dead. Usually it just won't idle very well. Every time I have had a MAF go bad on a car it has just effected the idle.
 

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Vanilla Ice all the way baby!
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have the ecv check, and the only reason a check engine light would come on it for an emission related failure, thats the only thing the CEL comes on for

i ahd a similar problem with my 87 NA and it was the ECV, which suprisingly didn't set a light
 

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JAMESZ said:
You can rev the car past 2000 if the MAF is dead. Usually it just won't idle very well. Every time I have had a MAF go bad on a car it has just effected the idle.
We've had several threads here that beg to differ. I suggest you use the search. ;)
 

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Discussion Starter · #8 ·
Sorry haven't put enough details about my car.

Nissan 300zx Turbo 5spd Manual Transmission

I can rev past 2000 rpm, I can red line it. It only hesitates when it's idling.

Im pretty sure they didn't know how to pull up the self diagnostics mode and that's why they got a whole bunch of sensor failures that don't even show any affects towards the car.

Other than the trouble codes, has anyone had this same problem? Im going to perform my own Trouble shooting with the ECU and i'll find out the true trouble codes for my engine.

Thanks for all the help, but keep a look out for my next post as to the true trouble codes and what can i do to keep my Z31 going!

Thanks
 

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nambino said:
Sorry haven't put enough details about my car.

Nissan 300zx Turbo 5spd Manual Transmission

I can rev past 2000 rpm, I can red line it. It only hesitates when it's idling.

Im pretty sure they didn't know how to pull up the self diagnostics mode and that's why they got a whole bunch of sensor failures that don't even show any affects towards the car.

Other than the trouble codes, has anyone had this same problem? Im going to perform my own Trouble shooting with the ECU and i'll find out the true trouble codes for my engine.

Thanks for all the help, but keep a look out for my next post as to the true trouble codes and what can i do to keep my Z31 going!

Thanks
Pretty sure the idle switch is your problem. Without it the ecu has no reference for when the car is at idle, or coming off idle. It can tell somewhat due to MAF flow increases, and 02 sensor readings, but other than that it's pretty much blind.
 

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ZPOOLNZ
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♣Zen31ZR♣ said:
We've had several threads here that beg to differ. I suggest you use the search. ;)
Yeah I have answered all of those threads the cars didn't always stop at 2k. Usually there is alot more wrong if the car is hitting a dead point. With the MAF dead the car will rev past 2k rpm there is nothing to stop it from reving. It will just have trouble idleing. Ive had the same thing on the Jetta the MAF goes bad every now and then and it just won't idle very well. I've been in a Z31 diagnosing problems before and the car had a bad MAF and it just wouldn't idle.
 

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Hey, I'm just trying to help the guy out. Based on past experiences, I think it's the idle switch. You could be right, but I gotta go with what I know. Based on price, the idle switch is a lot cheaper to replace. I'd have it tested or swap another one in, at least.
 

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Discussion Starter · #14 ·
Thanks everyone, im going to try some of these things this weekend. It might also be my Air Regulator, because the sensor hookup is in bad shape. I'll let you guys know what I find out!

Thanks again!
 

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nambino said:
Thanks everyone, im going to try some of these things this weekend. It might also be my Air Regulator, because the sensor hookup is in bad shape. I'll let you guys know what I find out!

Thanks again!
The air regulator should have thrown a code, too, if it was not properly connected.
 

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MAF

♣Zen31ZR♣ said:
The air regulator should have thrown a code, too, if it was not properly connected.
When mine went, i'd get 1900 RPM...that was it...the ecu threw a code 21...the idle increase to 1200 and ran smooth but nothing, and i mean nothing over 1900...200 later and a new MAF it was fine...follow the self diagonsis in the factory service manual...do just as they say....it told me exactly what was wrong and saved me from replacing the coil and other high dollar parts...good luck
 

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What does MAF, ECU, ECV stand for?

I've had this same problem with the idle for 2 months now. It's easy to put off during the week but I've got to fix this. About 6 months ago I was having this same problem and the mechanic replaced I think, it was called the fuel filter regulator and fuel filter. It was something along that and it fixed the problem that I'm having now. He's so expensive just to walk in and I'm trying to fix anything I can.

So my idle problem for 87 300 nt has to be; MAF, ECU, ECV, Fuel Filter, Idle Switch, or check the wires under the black box to see if there connected?
 

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MAF = Mass Air Flow Sensor
ECU = Engine Control Unit
 

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♣Zen31ZR♣ said:
The only code I see in the above that would affect how the car runs at idle, is the idle switch. The speed sensor might, but I think thats more in the newer vehicles. The fuel temp sensor only affects the engine on startup on a warm day or if vaporlock might be present. Neutral switch? I must assume you have an automatic.

I'l put it like this, if the MAF was not working properly, you would not be able to rev past 2000 rpm. So you can pretty much stop worrying about that.
The idle speed switch is the little black box on the driver side of the TB. It's either bad or likely unplugged, or the wiring is bad. Check that first, it's probably the cause of your problem.

I checked under the black box and all 6 wires were connected. Also, I didn't see any lose wires or connections. Then again, I might not even be in the right spot.
 
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