so tonight when i was leaving work i plugged in my modis to see what my data stream looks like { ive been waiting to do this since i bought it}, i looked up any codes and got code 42? now ive had a high idle issue for months now. it starts off when cold around 1500-1700 rpm then takes 3 mins to come down to the 550 i set it at. it sometimes will sputter from a hard deceleration and it starts running very rich. the whole ignition system is new. plugs, wires, cap , rotor, distributor, icm, coil, etc. wires are taylor, coil it msd, dizzy and rest are all napa. icm is ac delco from dealer. anything im missing here and why doesn't this code set of my ses light? for the unknowing: the modis is a snap on scanner. im a mechanic for a living but find myself stumped today.

 

OBDII(95 & later) will keep the MIL on for any MIL fault code, until the code is cleared from memory, or for a given number of key cycles(depending on the manufacturer). The OBDI(82-95) will only turn on the light when the problem is present. The code will remain in memory for 50 key cycles after the problem has last presented.

On dastastream, how does the O2 voltage look? How does it look when the poor idle and rich condition exhibits? Using the Modis, perform the IAC test(if available), in the actuator test list. Clear code 42, as it can cause issues with EST timing control. This code will be set anytime you disconnect the EST bypass to set timing. After clearing codes, drive the car in conditions that would cause the failure(recreate failure). See if the code returns.

 

ah someone familiar with the modis. i believe i stumbled on the problem today tho. it seems the knock sensor itself is suffering from age. the actually sensor crumbled when i touched it to make sure the connector was tight. the problem is kinda hard to recreate and just happens random but there is a light at the bottom of a hill that it seems to happen mostly. like said rapid deceleration. still not sure if it explains the high idle at start up. it also doesnt turn the mil on when it is doing this sputtering either. not much seems to turn it on. only setting timing{ unplugged est}. my vacuum hose was broken to the map and even that didn't set a code. just boggles my mind these older computers.

 

Like any other internal combustion engine, it needs fuel in the right amount, sufficient spark in the correct time, good compression and unrestricted airflow. The high idle at cold start is normal. It should start at close to 1800 and work its way down to normal warm idle in 30 seconds or so. Code 42 is strictly EST timing control. The knock sensor will set a code 43 for ESC system fault, if there is a problem with it.

Use the modis to view data and look for indescrepancies in coolant temp between ECM data and actual(you'll need to use some common sense and maybe an infared thermometer). Check injector spray pattern. Since i'm sure you have a dial back timing light, use it to view injector spray pattern by dialing it back to time with injector pulses. This gives you a very clear picture of droplet size and shape of pattern. It should be a fairly solid cone with small even droplets. On throttle snap, the cone should expand to touch the sides of the throttle bore. If there is any question of spray pattern, suspect low fuel pressure. Check fuel pressure using the correct adapters from the master fuel pressure test set. Sweep test TPS using the Vantage function of the Modis. If fuel pressure is normal(9-13psi), and injector spray pattern is abnormal, remove injectors and have them serviced.

 

ok. i know the cone is good but i did notice that it starts sputtering pretty bad when it does this stumble. it wont die but just keep idling between 300- 650 rpm. i have 13 psi fuel pressure. i just replaced the pump recently. lol ill do the rest later on when i get the ole ladies truck running right.