Totally stumped- Nissan mechanics?

[Pritch]

Hello there!

Well folks, Pritch's daily driver is sick. Im through trying to diagnose it, ive even used the shop service manual with no luck. If anyone happens to be a Nissan Mechanic or know one, it would be great. Or just if you have had any experience with these fussy older models.

Symptoms:

Idling, it will occasionally "miss". It goes POP....POP...POP like its misfiring. Sounds like someone playing a bass drum under teh hood. Sounds like a bad plug or wire but it only does it so often...and seems to like doing it when its hotter and more humid outside than when its cold. Also no missing when you accelerate. Im not sure but would a bad wire or plug miss all the time or just under idle, no load?

Also, idle is so fussy...sometimes it idles at 500 revs like its supposed to, sometimes 1000, sometimes 1500 even. Coasting to a light sometimes the revs will even jump up without pressing the gas. Power delivery at LOW revs ie under 2500 is lumpy

Vehicle is a 1993 Nissan 240SX, 2.4 Liter 5-speed with intake, header and exhaust. 270,000 kms and otherwise no modifications or problems.

Any idea?

[ASQ]

Generaly speaking there are two major system in a car engine. The feul system and Electric system.

When it revs up and down the Engine is getting erratic feul supply may be because of mechanical linkage needs freeing up , or may be Electrinic control system is malfunctioning(if it is installed).

And Pop Pop sound could also mean many things, may be the coil if it is on this car is failing, may be the electrinic board supplying current is failing, after all the car has 270,000 KMS.

To check these problems u may have to consult the service manual of this car by the Manufecturer or look for a generic service manual.

Good luck.

[apl16]

hmmmm....have seen nissans with weak fuel pumps.....maybe poor fuel fix with fuel conditioner or fuel filter partial plug......maybe issue with distributor cover crack allowing moisture in.....good luck!

[Pritch]

seems ignition related yes......weird thing is how it is sensative to temperature.....

[Roadstar]

Did U check the manifild for cracks ?

[ASQ]

It could be as simple as a loose wire or broken wire on a plug.