96 GA 3.1L irratic idle

[meow700]

I have a 96 GA with 226k, with the 3.1L it seems after the car warms up it has an erratic idle when in park, also while in drive as long as I'm not giving it gas sometimes its so erratic the car stalls....this does not happen everytime sometimes I can leave it running all day long but it does do it enough to where the car is undrivable.

[3100]

What are the rpm ranges when this happens?

[meow700]

i would say between 200-1200rpms

[Scrapper]

it could be your iac (idle air control) or your tps (throttle postion control) and have you checked for a vaccume leak?

[3100]

lift that cover under your shifter leader boot you will find this part (sorry don't have a better picture) the only picture of this part I could find was here

http://cgi.ebay.com/ebaymotors/CHEVR...QQcmdZViewItem

so disconnect this and see if it will start with this disconnected and if the same symptoms will continue? There is a microprocessor inside that gets shorted and causes similar issues. I know that it is not the same part. You have prnd123, but you got the idea.

[meow700]

It already has a brand new iac and a tps. But the shifter module.....never thought of that is there anyway to test it??? if not im sure i can get one for cheap from a junk yard...Thank you so much....will let you all know if this works

[xeroinfinity]

other then the IAC causing erratic idle;
- lower intake bolts loose or cracked vacum hoses
- leaking or clogged EGR or PCV valve(s)
- clogged dirty nijectors
- or faulty ignition system
- worse case, worn timing chain, low compression from leaking/bad valves, worn out cam

[3100]

for now just see what happens if you disconnect prndl's connector

[meow700]

it acted the same way when i disconnected the PRND21 connector....on a different note i was driving through town today and it died at like 35mph. i restarted it and it would idle great but died every time i gave it gas. i had to hold it to the floor to keep it moving and it would rev up backfire and die..then barely save it self...and then do it all over again...after i limped it home it has not started since.

[3100]

check your transaxle range switch on top of your trans (below your power booster you will see black swithc and and shifter cable coming to it.)


this are wires coming to your trans swithc check them with your dvom if you have one when you are in P blk/wht wire should have continuity with ground, yellow is open, grey is open, white should have continuity.
Make sure switch is not loose, also check connectors make sure they are not rusted, also open the hood and tell someone to shift from D to P while you are watching the movement of the shifter cable and switch arm. If you see that switch arm is moving in one direction and then stops, then you try to move that arm in the same direction bit more just to see if the shifter cable is loose and not pushing arm of the range swithc far enough to make a good contact inside of the swithc. At that point if idle improves then you will have to adjust the switch. Again Prn123 switch communicates with pcm and if pcm does not know in what gear is the transmission IAC, EVAP, EGR sensors will be confused.

still when you get chance to visit junk yard get that prnd123 module they will not charge you more than 3-5$ sometimes they will let you have it for free. Did you try reconnecting prnd123 and starting again?

[meow700]

Yes, the PRND21 was hooked back up when the car messed up this last time...My question is would the shift module cause the car to act like this and not restart? shouldn't the car at least start even if it doesn't know what gear its in?? I'm wondering maybe if the Crankshaft positioning sensor went bad(although it only has about 30k on a new sensor). I'm also wondering why it went from irratic idle and dieing to backfiring and dieing under acceleration....the only thing it would do right today was idle...it would start right back up everytime and idle while trying to get it home....then when it cooled down and i went out to try to get it into the driveway a little better is when it wouldnt start at all....i have also checked a bunch of wiring because the harnesses are starting to get a little brittle with 227k miles of engine heat...

[3100]

- check main CKP sensor signal set your DVOM to read mili Volts in AC disconnect the two wire connector on the right side of the icm (you facing icm your right side) yellow and purple (twisted wire) is for your main CKP sensor connect your dvom leads to that connector and tell somebody to crank the engine for you, you should be getting around 200mV AC
- check your MAF sensor (clean if necessary)

[3100]

the prnd123 connector has 3 wires: pink ckt1020 that is 12+, black ckt 150 that is ground and tan ckt 800 that is for UART

tan wire is transmitting important coded data to pcm so if that module is bad pcm will get wrong data and will confuse EVAP, IAC and EGR sensors
so in your case it is obvious that something is confusing your IAC when your transmission is in P

tan wire splices in two places s277 and s278 and connects to c207 connector, then continues and connects to connector 1 pin 14 or 15 one of them should be tan wire. I will find this splice and connector locations so you can check them also.

[meow700]

I checked the 3x CKP sensor (yellow and purple) and it tested bad...after i replaced it the car will start right up and idle all day....but when i accelerate the rpm gauge goes berserk and does match engine rpm also the car will not accelerate and will only do about 35 to the floor popping and carrying on.....also it doesnt want to shift right which i am sure has to do with whatever is causing the possessed rpm gauge

[3100]

how is your vacuum modulator, remove the rubber hose from the modulator and see if any ATF oil is coming out,
- if your vacuum line to the modulator is bad or disconnected you can have similar problems
-do you have check engine light on?
- test your fuel pressure, It could be low. For now to test, you can unplug fuel pressure regulator vacuum line this will increase your fuel pressure test drive it with FPR line removed.
- check your trans oil level