both my 91 RS 3.1 and g/f's 92 Firebird 3.1 are having the same problem as always. swear i think the cars are joined together somehow. anyway it isnt constant or even slightly regular but when slowing down at a stop sign or stop light the cars sometimes hesitate and drop idle to the point their ALMOST about to die then pick up around 1100-1300rpm then idle back down to running. Mine has never actually died when its done it but hers has once . On my car atleast ive replaced plugs , wires , distributor , map sensor , injectors , fuel pump , fuel filter , 02's and has a dynomax muffler with high flow cat within the last 5 months . No chip or anything in the computer. Hers has a complete new engine with all new sensors along with a new ECU. All the vacume lines and everything are fine. Its only happened maybe 2 or 3 times in the last 2 years having the cars but just curious what could be causing it.

 

it could be bad gas. id check that first.

 

Clean or replace your IAC

 

check your voltage gauge regularly to see if your voltage is slipping under a bit when driving normally and watch it as you brake (not consistently, please watch the road as well). I know some will say well the drop in voltage is caused by X and Y so it doesn;t mean anything. Well on occassion mine will drop down a little and then pop back up. Doesnt do it as often now because I bought a new terminal for the battery, added a dual connector, cleaned out the bolt hole in the battery, and added electrical grease to all the connections.

The effect of the voltage drop would cause my car to be rough when braking, i.e. rpms dropping dramatically. Except with mine it doesnt pop back up, the voltage stabilizes and the car remains at about 650rpm. It only does this when the engine is warmed up though.

Just something to think about as well, plus couldn't hurt to clean it up anyway.

Dave

 

mine did that, take apart the IAC housing, and clean the crap out of it, its the 5 torx screws on the top of the inlet for clean that housing and then clean the IAC motor, i spent all kinda of money on sensors and crap and it turns out i that was a major problem also you may want to get some carb cleaner in the intake and also clean the throttle plate thingy, basically our cars are old and need to be cleaned

 

It is the IAC, it needs to learn idle, it takes forever on these 3.1's.

Their is some procedure to do this, but its best to just drive and let it learn.

Every time you dx the power to the ecm, it has to relearn.

 

OK , i cleaned out the entire fuel system along with the valves and everything when i took the top end off and replaced the injectors and everything , the IAC was also replaced not to long ago. Forgot to type that. computer was saying it was bad when i pulled the throuble codes. Thats been about a year ago. Im thinking it may just be as said that the car forgets where its at because it only seems to do it right after the batterys been DC'ed for awhile then after driving it stops and acts fine. I was just curious if it may have been anything else other than crappy ECU lol. Also does anyone have thoes ECU savers that plug into the lighter and run off a 9 volt battery? curious if thoes really work

 

YOu're never gonna track this down...give up. If you can't duplicate the problem, then it's near impossible to troubleshoot it. I get customers at the shop that come in and say that "my car dies" so I ask them when and they say, sometimes driving, somtimes stopping, somtimes idling, but then you ask tehm how often it happens and they say it happens once every 6 months. I ask them if they really want me to spend 2 hours diagnosinging the problem, just to tell them that nothing is wrong because I couldn't get it to happen.

When the problem gets bad enough to happen regularly, then worry about it. It's not worth losing sleep over.

 

Well, believe it or not. I went through the same things with
my 92 RS with a 3.1L. After all else it came down to the battery.
Battery appeared to be fine. Started easily. But, it was at a
voltage level that was just low enough to throw the IAC off
once you allowed for all the aged connections through out
the car and the idle dropped (lower alternator output). Mine would die often at stop lights. Did everything everyone has suggested here but did the battery at last resort. Noticed
that I would get funny static in my radio and my cruise would drop out occassionally when I hit a bump. And then one day
it wouldn't start, battery was down. Hope this helps.