Smoking Stuttering Stalling Backfiring etc. etc.

[nightshift]

I have a 1991 240sx with about 120000 miles on it the engine though was rebuilt last year around this time of year.

Since May its been having a nasty Idle which hasnt been much of a problem since It only goes to school and back. Lately though its been getting worse. I replaced the sparkplugs that were crispy black and cleaned out the electrical connections around the car and its still getting worse. Pulled out the plugs today to give them a check and they were black and crispy. The odd part is that as long as I have my foot on the gas the car runs fine . . . well at least on the highway or hauling *** (after stalling at an intersection some idiot in a civic thought it would be cool to rev on me so I proceeded to spank the crap out of him and then let a big nasty smoke gas fart out at him when I slowed down) but as soon as I slow down to say normal street speeds is does all of that stuff up there in my title and if I take my foot off the gas it doesnt even idle just drops the needle and stalls.Ive checked for loose hoses and havent found any and all the sparkplugs are firing we checked em when we pulled them out today. Please :help !

[NISTECH]

your runnin fat. check your airflow voltage out put,about 1.3 to 1.4 volts at idle. check your coolant temp resistance(2 wire one) see if it thinks the car is cold. also check your coolant temp sensor.Engine Coolant Temperature Sensor TestWith an ohm meter check resistance of sensor at specified temperatures.TEMPERATURE:20°C (68°F)RESISTANCE: 2.1 - 2.7 K ohmsTEMPERATURE:90°C (174°F)RESISTANCE: 0.24 - 0.26 K ohmsTEMPERATURE:! 10°C (230°F)RESISTANCE: 0.14 - 0.15 K ohms

[p00t]

in addition to what nistech said i would also check the 02 sensor. it appears your running very rich, so it has to do with your ECU moderating the A/F ratio.

might be your timing also? maybe they screwed it up when they were putting it back together? gotta check that!

[nightshift]

I got around to testing the MAF signal and it goes between 1.55 to 1.62 when the car is already warmed up so is that way out of spec? what the remedy? as far as coolant temperare sensor I think my voltage meter touched something it wasnt supposed to while I was trying to get to it cause it doesnt read anything on anything anymore. . . . . . anything else I could check?

[nightshift]

thank you thank you nissan Gods . . . . . errrrr I mean Nistech after I checked the Voltage it occured to me that I had the original MAF sittin around the garage so . . . . I put it back on and the one that was just on the car looked NASTY inside the old one was clean . . . I dont know why I took it off. Neways car still sounds like crap but the voltage checked out right at 1.29 neways so I drive the car out to an open road and floor it so it can burn all that gas that was in the system . . . . . car runs perfect now . . pegs 750 at idle and accelrates nicely.

So just as a follow up I should probably change the plugs again to some new unfouled ones and check the timing that I probably messed up trying to fix this and what else?