I had this down in TPI, and I am thinking it may be computer related, so I will try here as well.

I had the all too typical occasional idle surge and frequent stalls at lights. But after some driving and a new temp sensor, everything was great. I drove it for 2 months without 1 problem. I changed my battery as the other tested as a bad cell, and immediately my car is not just bad, but worse than before. Before it would happen in restarts, now it doesn't matter. And by immediately I mean the first time I started it with the new battery this problem reemerged.

At the end of my rope, I did the paperclip trick despite never seeing Check Engine light during these bouts.

It just flashed 12. Nothing else.

So I decide to start the car (last time it ran last night it was running rough), it ran like a dream. This is really stupid. Do I have some sensors that are working just enough to keep from throwing a code?

The injectors are freshly rebuilt. I even have the spray datasheet. The pump was installed by a garage at the same time as the injectors a couple hundred miles ago, but I guess it is possible the pressure may not be 100%. I don't think the problem is to little fuel as it is running rich when it acts up.

I managed to get the car to act up again after the test. It was idling over 2K RPM's. When I unplugged the TPS, it dropped a little (to about 1K), but not to normal. I also noticed the Check Engine light came on. Plugged it back in, it went off, so the light works as it should, but the idle shot back up to 2K. It got really rough, and the exhaust was really rich and it died. I had a hard time restarting it, but managed to. It was rough, high idle , real rich, then BAM, it went to normal. Smooth 600ish rpm, no longer rich, it is like normal. Took it out, drove it for 30 or so miles, pulling over here and there to shut it off and restart and it is running smooth again. It will not act up again, for now.

So what can be acting up that lets it run perfect for a while weeks, months, and hundreds of miles, then turn to crap without warning and without the computer seeing it? Just to snap out of it and return to normal?

Plugs, I am not sure how old they are. That is a good idea. They may have been changed with the injector job, but not sure, I will dig up thy invoice. The wires are brand new.

The fan works now that it has smoothed out.

Any suggestions? Has my computer been resetting and these bouts are during its re-learning stage?

 

maybe a loose ground wire somewhere.

 

i know im not any help.... but ive had weird issues before with crazy rpms at times and no time frame... just erratic. it was a shitty deteriorated vacum line to the trans computer or something in the left front corner area, which went to the back area of my intake. car wounldnt star sometimes ran high rpms... but other days completley normal.. asked my buddy a mech... told me to check that hose and bam! thats what it was.... now i hollowed out the cat and put bigger exhaust on and changed the gear and have all sorts of other issues! ran great did a tunes up... was at -1 timing should be 6 or go more to 8 when i did this it sounds like your problem.... very rich somtimes shitty running stumbling engine no power then just like that its great.... wtf right.... guess its off to my mech when i can get in

 

agreed on grounds, make sure all ecm grounds are good, and if you have access to a scan tool, ie snap solus, otc, etc, look for anything odd, o2 mv, tps v, desired idle, pulse width, closed loop operation. Check for erratic timing change, check base timing, make sure intake bolts are all tight, make sure there are no vacuum leaks. It may be good to drive it with someone else with a scan tool hooked up, so if the check engine light comes on intermittently, the passenger can check it.