# 1993 maxima rough idle



## Moms93NissanMaxSOHC (Dec 15, 2008)

I am trying to figure out this rough idle, its not bad... the car runs and drives fine, but it just doesnt seem 100% to me. I replaced a fuel injector about a year and a half ago(That was a bad idle, this is nothing like that) it just has a slight miss at low RPMs. New plugs, wires, cap, and rotor did nothing. Every wire when pulled makes it idle like it has a dead cylinder(since it then did).

Could timing be a thing to look at? I have never adjusted that on this car, what should it be set at anyway? This car has well over 200K on it but its a great car, body is nice and it runs well... except for this.

Please help,
Craig


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## jdg (Aug 27, 2009)

Crank/Cam sensors?
Vacuum leak?
Fuel pump pressure? (which _shouldn't_ affect the idle if the high rev's are good, but...)


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## smj999smj (Jan 1, 2006)

Have you checkd for trouble codes? Performed a compression test? Made sure you used OEM parts during the tune-up? Check fuel pressure... Might try a professional fuel injection cleaning.


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## Moms93NissanMaxSOHC (Dec 15, 2008)

Can the crank/cam sensors be tested? I checked the vacume a while ago and I forget what the reading was but one of the more mechanicly minded guys at the bodyshop looked at it with me and said he didnt think it was a vacume problem. The fuel pressure may be something to look into other than it doesnt seem to be running at all rich... other than initial startup I can smell a faint fuel smell but nothing when hot(this is probably worsened by the small stress crack in the factory y pipe.. its on the list to replace!)


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## Moms93NissanMaxSOHC (Dec 15, 2008)

Also the car isnt throwing any codes, what should the fuel pressure be at? and is there any way to adjust it or just replace a regulator? As far as the tune up, I used NGK plugs and wires. I dont remember the cap and rotor... they were from napa auto parts I belive, but they also made no noticible differance to the idle quality.

I was thinking about getting the fuel injectors cleaned... I read a few posts about a SEAFOAM fuel system cleaner that I was going to try first(dont usualy have too much hope in the bottle fix).

Also, as far as the compression test, I never did one... what should it be? or is it more important that they are relitivly even?

Thank you all!
Craig


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## jdg (Aug 27, 2009)

Time to get yourself a Haynes or Chilton's manual for your car.
Every one of your questions (fuel pressure, sensor testing, compression checking, etc) can be answered in one of those.


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## smj999smj (Jan 1, 2006)

The crank sensor is part of the distributor and I doubt that's your problem. The only test I know would be to monitor the spark patterns on an oscilloscope. If your exhaust leak is near the oxygen sensor, it could throw it off and be the cause of your rough idle. Fuel pressure should be about 36 psi regulated and it's not adjustable outside of the fuel pressure regulator's normal operation.


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## jdg (Aug 27, 2009)

I was thinking crank sensor 'cause at low rpms, the output from it _could_ be weak, but you'd figure that would set a code of some sort for random misfire or the like.


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