machine23

ive been trying to figure out my misfire and rough idle for months now. its keeping me from getting my car smogged. and i really dont have the money to take it in to a shop...

soooo....i was talking to my coworker...i explained that my check engine light doesnt come on by itself, but only when i jump the diagnostic port. and when i do that it flashes code 24. open or closed air temperature circuit. he was thinking my ecm was possibly bad, he thought it was odd that the light doesnt come on by itself but only when i jump the diagnostic port.

ive looked at my air temp sensor and got a reading of 1.6 ohms. which is slightly lower than it should be. i removed the sensor's wiring and soldered in a resistor of 2.2k ohm...the engine still ran the same. i reset the ecm and drove the car around for a little while. again, the cel never came on but i jumped the diagnostic port and sure enough, it fashed 24 again.

so i decided to make sure there was continuity between that air temp sensor and the ecm, and there is.

no other engine codes have come up.

so guys..what do you think?

Flash319

If it runs it is not the ECU. It is telling you that the air temp sensor in the AFM is NG. Your problem could be many things but I would start at the AFM and intake duct work. You may have a crack or leak. With the truck running pop the AFM off the air cleaner and put your hand in and move the flapper a bit by hand. Did the idle smooth out? If so then you have a leak.

Is it missing at idle or while driving?

machine23

yea it misses when its idling. and noticeable lack of power when driving. i did run the engine with the top cover of the afm off, and moved the afm meter by hand and the engine responded to that. it didnt make the misfires go away though. and there are no leaks in the intake tubes

abecedarian

Did you clear the codes after working on it?

abecedarian

Reading a little more...

You've set the timing and idle speed where they belong, checked your valve clearances, no vacuum leaks, throttle position sensor, etc.?

Done a compression test? Had your injectors checked for flow and pattern?

Flash319

Run it at night and look for arcing around the coil and wires.

abecedarian

During the day, you can also use a spray bottle full of tap water- set the spray to the finest mist (non-aerosol / pump hairspray bottles work excellent) and spray around where wires are near metal. If the idle changes / engine misfires, you've found weak insulation in a spark plug wire. Even if you're really brave, do not try using a mix of water and alcohol or even straight alcohol.

The water mist will lower the resistance between the wire and metal and make it more easy for the current to jump. It will often be accompanied with a 'tick' when the spark jumps.