My car has been givin me a lot of problems latly with the cat. converter, but recently (yesterday) i drove it about 550 feet down the road, seemed fine, until i stopped, then the idle dropped to about 450rpm, then it dropped to 0 rpm. The car wouldn't start at all, or it would start for a second, go up to 500rpm, then drop right back down to 0. I used a code scanner computer and i came up with 3 codes. Code 12 - No reference pulses to ECM. Code 34 - MAF sensor - signal voltage or frequency is low during engine cruise, OR MAP sensor signal voltage is low during ignition on. And code 42 - Electronic Spark Timing (EST) Circuit - open or shorted to ground during engine run OR Direct Ignition System (DIS) fault - bypass circuit open or shorted to ground during engine run OR Fuel Cutoff Relay Circuit - open or shorted to ground. Any ideas on why it just drops idle like that and dies out? Any replys appriciated, Thanks.

 

mine just started this too, i dont why this is now happening. it doesnt do this if i put it in park, just in drive when i am at a stop light. it really starts chugging then the RPMs drop down. i havent let it stop the engine yet cuz i throw it in park b4 it gets there.

 

Yea, if i leave it in park, the rpm's will float at about 500..... but if i knock it into drive, then go, then stop at a light or sign or something, the rpms die down to 500, then chug, then die.... i have no clue what its doing.... Any one out there have this happen... help?!

 

I'm sure you'll get lots of good advice. Just take a minute to tell us what model/year/engine you're talking about.

 

1988 pontiac firebird 2.8liter mpfi I dont really think it has anything to do with the actually engine though. Im pretty sure its a sensor somewhere.

 

Mines a '87 T/A, 305 TPI.

Thanks!

 

khellendros,
after searching the board for a while i came across people with similar phenomenon and the fix was usually the IAC valve.
i replaced mine tonight and i fixed 95% of the problem!! the RPMs dont jump around crazy anymore... it doesnt moan and lurch when i stop anymore... it does idle fairly low at stop signs, about 550RPM, but it stays there pretty steady! i got the IAC valve at AutoZone for $33. the biggest PITA was taking the darn original one off.
let me know if you need anymore details.

 

Thanks a bunch, that is what i thought it could probally b. I appriciate your response, i'm gonna change it tomorrow. We'll see what happens. Ty again.

 

Mine is doing the same thing. Where is the IAC valve located at. Thanks for all the help

 

Just emailed you a pic.
Its called the IAC stepper motor in this picture of the throttle body. Its on the passenger side and will have a square plug with 2 green wires and 2 blue wires going into it.

There is also a reset sequence you need to do to have it relearn the new piece/driving style.

It unscrews like a bolt, but mine was a real b.tch to get out cuz its in a hard to reach place and was stuck in there real good from old age.

 

$33 for a new IAC, of $4 for a spray can of carb cleaner? Either way, the IAC has to come out, so you might as well try cleaning the original first. It only takes a little bit of dirt and varnish to cause a sluggish IAC:

 

Vader,
went to adjust my minimum are screw so that i can keep it above 500 rpm in drive, which i think will fix all my problems. once in a while it will drop to 500rpm and then start struggling to stay above that. although its much better and stable after changing the IAC. well, my minimum air screw was missing! (i think) all that was there behind the thing that moves with the cable was just the threads. does this mean its adjusted to the max idle or min idle? i.e. if i find a replacement screw somewhere will this let me increase my idle? what does this mean and what should i do now? would the dealer carry the screw?

thanks!