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.

It is a 1991 305 TPI Firebird, I just replaced the injectors, new fuel pump and filter. No lights are flashing on the display.

 

It could be a bad ground not letting the Alternator charge the Battery !!! P.S check your vacuum lines too.

 

I checked my lines, again, and I am not finding any leaks.

I do believe my battery problem was because my rear hatch motor was burned out. I disconnected it, but the battery was already damaged from being perpetually drained (my car is not a daily driver, I may put 3K miles on it a year).

I was out looking the lines again and had it running. It is doing the high idle thing and what is also different is my primary fan is not coming on! Before the battery change when all was cool the fan would kick on as soon as the gauge hit 220. Now its at about 230 and still not on.

 

bump

 

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?

 

May not be much if any help, here's what I would check::

All injecters working, spray pattern is consistent.

Plugs are firing & not old // fouled.

Plug wires are good-- check in the dark for glowing // arcing
jumping across wires as car idles. { Set parking brake for added safety!! }

Test fan for power { IDK how they do it, but there's a couple threads
somewhere detailing this }

Check rad hoses-- make sure they ate not soft & mushy.
See if lower rad hose collapses when RPMs are raised.

(edit )

I guess it would be dificult to check injecters-- sorry!!
Check fuel pressure??

 

The injectors are fresh. 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.