Mechanics

ROUGH IDLE WHEN COLD

1993 Nissan 300ZX • 6 cylinder 2WD Automatic • 123,000 miles

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
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Bounty Hunter
January 3, 2011.



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 3.

http://z.about.com/d/autorepair/1/0/Z/O/nissan_dtc-test.gif

Post Codes for further info...

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Obxautomedic
Jan 3, 2011.
It idles like it is chocking on too much gas. Fumes bad

Tiny
Bounty Hunter
Jan 4, 2011.
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

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Obxautomedic
Jan 4, 2011.
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

Tiny
Bounty Hunter
Jan 4, 2011.
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.

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Obxautomedic
Jan 4, 2011.
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

Tiny
Bounty Hunter
Jan 4, 2011.
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....

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

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Obxautomedic
Jan 4, 2011.
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.

Tiny
Bounty Hunter
Jan 4, 2011.
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.

Obxautomedic
Jan 4, 2011.
Sorry, was tired. It has been like 4yrs

Tiny
Bounty Hunter
Jan 4, 2011.
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