rough idle when cold

1993 NISSAN 300ZX
123,000 MILES • 6 CYL • 2WD • AUTOMATIC
Avatar
BOUNTY HUNTER
  • MEMBER
  • 8 POSTS
My 1993 300zx runs very rough from a new cold start in the day and then runs rough off and on while idling but not nearly as bad...had some injectors replaced and wiring and still not right....HELP PLEASE
Jan 3, 2011 at 10:06 PM
Advertisement
Avatar
OBXAUTOMEDIC
  • CERTIFIED EXPERT
  • 3,711 POSTS
Hello,

Ok, when was last tune up? Worn Plugs, Corrossion on the Electrode in the Distributer Cap, Vacuum Leaks can all cause your problem.

Is the engine light on? I f so will need to pull codes...

1.Access the ECU and position it for observing the diodes.
2.If the engine does not run, turn the key on and proceed to step #4.
3.Start the engine and warm it to operating temperature then idle.
4.Turn the diagnostic mode selector on the ECU fully clockwise until both diodes flash 3 times then turn the selector fully counterclockwise. The ECCS system is now in mode

Post Codes for further info...
Jan 3, 2011 at 11:40 PM
Avatar
BOUNTY HUNTER
  • MEMBER
  • 8 POSTS
it idles like it is chocking on too much gas...fumes bad
Jan 4, 2011 at 12:11 AM
Advertisement
Avatar
OBXAUTOMEDIC
  • CERTIFIED EXPERT
  • 3,711 POSTS
Ok, Sounds like you have a couple cylinders that aren't firing.
Loosen plug wires so you can pull them off fairly easy, start vehicle, and one at a time pull plug wires off noting any change in engine. Make note of any cylinder that does Not change engine rpm's.

post findings

.
Jan 4, 2011 at 1:03 AM
Avatar
BOUNTY HUNTER
  • MEMBER
  • 8 POSTS
but it has black smoke .....if you rev it up it is like it cleans it out for a min. so if you say that ...what would i be looking for
Jan 4, 2011 at 1:13 AM
Avatar
OBXAUTOMEDIC
  • CERTIFIED EXPERT
  • 3,711 POSTS
Ok, the black smoke is an indication of the engine running rich(getting to much gas).

With the engine running and taking off one plug wire at a time paying close attention to how the engine responds each time you can narrow down which cylinder or cylinders are causing the problem. We can then proceed to determine the cause, whether it is electrical problem or mechanical.

.
Jan 4, 2011 at 3:32 AM
Avatar
BOUNTY HUNTER
  • MEMBER
  • 8 POSTS
Iknow I am asking alot but if it is not the plugs or wires...what then? It runs great under excelleration and most times idling when warm
Jan 4, 2011 at 3:56 AM
Avatar
OBXAUTOMEDIC
  • CERTIFIED EXPERT
  • 3,711 POSTS
Hey, no problem.

Ok, lets back up a little. Reading back I had aked when the last tune up was? And you never answered.

If it has been a while pull a plug or 2 and look at the condition and also remove cap and take a look at the inside, especially the electrodes if they look like there's a lot of corrossion on them try cleaning them off a best you can and also clean off the tip of the rotor. Put back together and see what happens.

Check out the link below for Plug conditions....

https://www.2carpros.com/articles/how-to-change-spark-plugs

.
Jan 4, 2011 at 4:35 AM
Avatar
BOUNTY HUNTER
  • MEMBER
  • 8 POSTS
If there is alot of fuel going in, that could be stuck injectors? Are thry hard to replace and how do i know if it is them,,,,,,
Jan 4, 2011 at 4:50 AM
Avatar
OBXAUTOMEDIC
  • CERTIFIED EXPERT
  • 3,711 POSTS
Could be stuck injector or injectors. You said you had some of them replaced along with wiring. However, if the spark is not strong enough to completely burn the fuel that is sprayed into the cylinder you will get same results. Once engine heats up it will burn the fuel a little better do to engine temp, but when cold it won't burn as completely.

So, once again when was last tune-up?

I am trying to narrow it down but if you won't answer my questions back to you , it is pretty much impossible.
Jan 4, 2011 at 3:20 PM
Avatar
BOUNTY HUNTER
  • MEMBER
  • 8 POSTS
sorry, was tired...It has been like 4yrs
Jan 4, 2011 at 4:55 PM
Avatar
BOUNTY HUNTER
  • MEMBER
  • 8 POSTS
Ok now i have the whole story...I chked myself...When I stert it it runs perfect for 5 minutes and then idles rough and slows down.to a vibrating idle....then as it warms up more it runs fins again....there was a recall on an item yrs ago....would that be the prob or something else...ty
Jan 5, 2011 at 1:14 PM
Avatar
OBXAUTOMEDIC
  • CERTIFIED EXPERT
  • 3,711 POSTS
Ok, Possible causes...

TPS (Throttle Position Sensor)

IAC (Idle Air Control) Valve

Could be the recall item will take a look at recalls

Is engine light on? If so look at my first post above and pull codes, post them here.

.
Jan 7, 2011 at 2:33 AM
Avatar
BOUNTY HUNTER
  • MEMBER
  • 8 POSTS
first would it be easier to call me?
No code lite on
Jan 7, 2011 at 3:44 PM
Avatar
OBXAUTOMEDIC
  • CERTIFIED EXPERT
  • 3,711 POSTS
Sorry, but no it wouldn't I work 3 jobs. And am pretty busy. When I have a few minutes here and there I will get on here and answer questions. I receive notification that people have responded to question I have answered on my cell so I know that I need to respond back as soon as I can. And sometimes it will still take me 24 hours, do to my main job (EMT).

Ok, The TSB I believe you are talking about is for the Ignition Power Transistor Unit. It came out Oct. 1994 so i would think that the unit would have been replaced or caused problems before now.

I know you said the engine light isn't on but, see if by chance there are any codes in the computer memory.

.
Jan 8, 2011 at 1:18 AM