'94 Infiniti running rough

My 1994 Infiniti g20 began running rough and has lost power. Little acceleration. At a stoplight it idles rough, but is ok in park. Replaced the usual--plugs, wires, cap, rotor. After spark splugs it began running a tiny bit better. Also replaced fuel filter.

The day before I drove about 20 miles of dirt road. Not too bumpy, but plenty dirty. Suggestions, ideas? did u check the air filter?

is the check engine lite on? My account is having issues, so I had to create a new one.

Just went to Jiffy Lube and had everything checked and filled. New air filter as well. The check engine light didn't come on until last night. It flashed for a bit and now just stays on. Any help whatsoever would be appreciated. Thank you. the check engine lite being on is a big clue. it means the computer saw something it didnt like and stored a trouble code. then it turned on the lite to let u know.

so u need to find out what codes are stored and go from there. your 94 should have a obd1 diagnostic system, so u can pull codes yourself. this link shows u how:

http://www.troublecodes.net/infiniti/

let us know what codes come up. The first time only one code came up: 41- Intake Air Temperature Sensor. Later two codes came up: 41, and 34-knock sensor.

I read on a g20 forum about IATs. There was a heated argument about them and whether or not they affect engine performance. So, should I get a new one? Will it make that much difference?

As for the knock sensor--I read about the difficulty of getting it out and I'm hesitant to replace it. Some have said that the sensor will go off when there is bad wiring and not because of engine problems. a bad iat, or air charge temp sensor, can cause performance problems. its job is to tell the computer the temp of the air being sucked into the engine, and its one of the sensors the computer uses to adjust fuel mixture.

if a bad reading makes the computer think the air is warmer then it realy is, it will cause the mixture to get too lean and that can cause the problems u got. if it gets too lean it can cause engine knock. the knock sensor will pick this up and let the computer know. if it reports a too-long knock signal it can set a code.

like with any sensor, it could be a bad sensor or a wiring problem. a common problem with these sensors is they get dirty and yuck up the signal. i think your car allso has a mass air flow, or maf sensor, and the same thing can happen with it. since the trouble started after driving on a dirt road, this is something to look into.

get a can of maf sensor cleaner from the parts store. take the iat and maf sensors out and clean them thoroughly. let them dry off real good and put them back in. make sure the wiring connectors are clean and making good tight contact. it would allso be a good idea to follow the wires back from these sensors and the knock sensor to make sure there in good shape. make sure the knock sensor connector is clean and tight allso, and check for loose wires in the connectors.

then clear the codes from the computer and see what happens. if the car runs better and the codes dont come back, your done. if cleaning the sensors dont help and the wiring is ok, the iat can be diagnosed by checking resistance. i aint got specs for that, but maybe some body in the infiniti forum does. if so, we can tell u how to check it. Here's the update:

Clean the IAT and the MAF. No change. Checked the IAT with a meter and different temperatures of hot water as my manual suggests--worked properly.

Reset codes, the check engine light began flashing intermittently, but not on any specific rhythm. It sped up sometimes or others it would slow down and sometimes it would stay lit. Stopped, checked codes again and it read cylinder 1 misfire. Reset and drove again. Same flashing without constant rhythm. Stopped, checked codes--got code 55--no problems.

Same rough idle and also 6-7 mpg loss in fuel economy.

Unsure where to go from here. ECM connections failing? This just gets more and more interesting. Thanks for all the help. yep, this is getting intresting.

one thing u can try is with the engine idling, pull the connectors off of the fuel injectors one at a time, then plug it back in before going on to the next one. if u find one where the idle dont change when its unplugged, that would narrow the problem down to that cylinder.

id allso check wiring harnesses to make sure all the connectors are clean and connected tight, including at the ecm.

if none of this helps, with the weird ecm readings your getting, it could be a problem there. youd need a scantool that displays live data and freeze frame data, or take it some place thats got one, to dig into that.Car Repair Talk's forum.