1993 Onboard Computer Question

[JF5000]

Hello! This question has already been asked I’m sure. I also searched the forum prior to making this post and was unable to find an answer. If someone could point me in the right direction I would really appreciate it.

Situation: 1993 Pathfinder sat for 1 year without a battery. Replaced the battery and now the vehicle runs a little rough and does not idle well (low idle). My initial assessment is that the onboard computer has forgotten the settings for various electronic components.

Question: Will the computer learn the proper settings after several driving cycles like some cars do? Or will this require a manual solution?

Again your help in this matter is appreciated. V/r James

[SpecialWarr]

The computer ( from what I have read) is a learning computer but the drive cycle is set at 50 cycles initial and an additional 50 cycles to have a complete parameter guide. It should learn some settings within the first 10-15 drives and get "acquainted" with your driving in a 2-3 weeks period. after that it appears that it will re-learn some settings after the battery has been out for an hour or more..... this is just what I have noted over the last 4 years and $5000 of parts and installation of things!

 

Low idle? 500 ish might be in need of a MAF cleaning / throttle body cleaning / a good rip onto the highway at full throttle to clear things up. MAybe an adjustment if those don't work.

[adamzan]

It should run at 750 give or take 50 rpm. That is what the service manual says. You can adjust it but it requires unplugging a connector so you're not fighting the ecu.

[Slartibartfast]

The ECU shouldn't need to learn anything for the engine to idle. I've had power unhooked from mine many times, sometimes for months, and never noticed a difference in how it runs afterwards. This isn't a finicky modern ECU that needs idle re-learn procedures or other calibration because you replaced a sensor or because it's Tuesday. It should run just fine on its default settings. I don't know much about how or what these ECUs self learn, but I suspect it's just refining its fuel trims and timing curve.

 

My first thought is rodents. This is mostly because my '93 sat for a while before I bought it and had a rat's nest in the air filter box. It jammed up against the screen on the MAF sensor, blocking off the airflow and fouling the MAF itself. It actually didn't idle too badly but it had no power on the road. I would also check for vacuum lines popped off or gnawed off, damage to wiring (especially the spark plug wires), and the usual looseness/corrosion in the electrical connectors (wiggle the MAF plug and see if it changes the idle). You might check under the distributor cap too and make sure it's dry and clean in there. My second thought is that this thing sat for a year. Did you put fresh gas in it or is it trying to run on year-old gas? My '95 runs fine on old gas but then I did throw in some stabilizer before parking it.

 

If all of that checks out, I would check the throttle position sensor and the idle air control valve. Cleaning the throttle body won't hurt anything either, and actually freed up some power on my '95.

[JF5000]

Awesome feed back! Thanks!