Stalling Problems!!! HELP PLEASE!!!

My buddy has a 85 Z28 IROC with the 305 TPI nothing modded - an he is having a problem - every time the car gets warmed up it stutters runs real rough like bucks and barely moves an then bogs out to a stall then won't start back up we checked the vacume lines all of them are holding there pressure but we still cant seem to figure out what the problem is. Could it be this ? Idle Control Valve (IAC) or the PCM because the IAC is to control engine idle speed, while preventing stalls due to changes in engine load. The IAC valve, mounted in the throttle body, controls bypass air around the throttle valve. I know by moving a conical valve known as a pintle, "IN" toward the seat (to decrease air flow) or "OUT" away from the seat (to increase air flow), a controlled amount of air moves around the throttle plate. If engine speed is too low, more air is bypassed around the throttle valve to increase RPM. If engine speed is too high, less air is bypassed around the throttle valve to decrease RPM. The PCM moves the IAC valve in small steps called counts which can he measured using a scan tool connected to the Data Link Connector (DLC).
I also know the purpose of the (IAC) is During idle, the proper position of the IAC valve is calculated by the Powertrain Control Module (PCM) based on battery voltage, coolant temperature, engine load, and engine RPM. If the RPM drops below specification and the throttle valve is closed, the PCM senses a near stall condition and calculates a new valve position to prevent stalling.
:disappoin

But does that sound like that could be the problem cause not really anything else seems bad or like its faulting....
Please Throw in your comments an help me get this problem solved because the car is like undrivable once it gets warmed up until its totaly cooled back down all the way - it has run warm but then soon as we go anywhere it does that then dies on us....
:banghead: :banghead:

Your Help Is Much Appriciated!
Thanks,
Matt

I had that problem once in a 90 cutt supreme and it ended up being the injectors. test those and if that's not it check ecm for stored trouble codes, if none are there, start running tests on the ignition system.

We Ran A Test For Code Numerious times an nothing is coming up --- we had other problems an the codes came up but i read somewhere that code wont always come up or it might not come up if the problem is the (IAC) thats why its hard to tell ya know man.... an those are some sharp looking cars ya got there nj on keeping them in great looking shape

injectors are pretty steep so i wanna hear other peoples ideas an if all else fairs change the injectors ... thanks Genopsyde - that might be the key if we cant figure anything else out ...

you don't hafta change em unless they're bad, you can have them tested to find out.

oh alright - i know some people i dont think i have the equipment to test them but i should be able to have a friend do - most of them got odd shit like that- but what would have to be done do you know to test them? an hey thanks man - nobody else seems to give a shit about peoples problems but your cool - ya help people out - i like to help people to when ever i can - the way i look at it is if u help others then you will be helped in return ...

It doesnt sound like an IAC problem.. But you can pull the IAC out and check to see that you can move the spintle in and out.. If its stuck.. You can use a little carb cleaner and tap on it with a hammer to loosin it up.. BUt it should be replaced..

Is your engine light coming on?

You can also pull the EGR vacumm line off and try run it then.. If it runs good than your IAC is bad

my buddie had the same problem..it was the injectors. he got a pretty damn good deal on em too! I forgot where he got em.

If it is, I suggest staying away from cheaper "reman" injectors..

yeah...going cheap pretty much on any carpart is gonna get you in trouble.

the reason my buddy got a deal is cause his dads friend got a discount or some crap.

ok yeah so i guess its narrowed down to sounding like its the injectors or the IAC valve--- yeah we checked an the EGR seemed to work properly so thats why i thought it might be the IAC valve .... cause all the problems matched up so now its narrowed down to 2 things k thanks guys for your help an input...

oh alright - i know some people i dont think i have the equipment to test them but i should be able to have a friend do - most of them got odd shit like that- but what would have to be done do you know to test them? an hey thanks man - nobody else seems to give a shit about peoples problems but your cool - ya help people out - i like to help people to when ever i can - the way i look at it is if u help others then you will be helped in return ...
well, thx for the compliment, but to be honest i'm prolly the least helpful person on this forum, the rest of the guys just aren't very active this week so far.

you can test and compare the resistance value's of all the injectors to possibly rule those out as the cause. the IAC wont throw a trouble code unless there's a loss of return signal to the ecm. the only other thing i can think of would be the junk bosche mass air flow sensor that gm uses.

Ya he has another MAF sensor - if for a firebird but i should work -other wise he'll have to dump like 140-160 to get a new one...
thank you 4onfloor

well, thx for the compliment, but to be honest i'm prolly the least helpful person on this forum,

He aint lyin!

When I said to unhook the vacuum line at the EGR.. That wasnt to test the EGR its to test the IAC.. If you have a bad IAC and unplug the EGR vacuum line, your stalling and rough idle should stop

Damone, yea, you better agree.

If you have a bad IAC and unplug the EGR vacuum line, your stalling and rough idle should stop

that only works if the pintle was all the way out when the IAC died. if it's all the way in, it'll probly just make the problem worse

test fuel pressure durring the stall condition. hook a guage up to it and watch the pressure as it dies, it should stay high, im not sure exactly what it should be on a TBI, probly 30-45psi, but what youre looking for is a constant pressure. or as the engine dies, the pressure will actually go up, because it isnt being released from the injectors anymore. if fuel pressure goes down, your problem is a fuel pump.

try the other tricks to diagnose the IAC, which it very likely could be. but pull it off and visually check for resin build up or other carbon deposites, that may lead to a malfunction of the valve. if the throttle body is all carboned up, then have an induction service and throttle body cleaning done. this will clear it up. if not replace the IAC.

i would look to the injectors as a last resort, the possiblity of all of them failing at once is very small, unless you got a tank of bad gas or something. my best guess is that its either the pump or IAC. good luck


oh and side note, please dont make the noobie mistake that all to often happens here. that just because you dont get alot of replys that no one cares, i for one have been very busy in my real life and have neglected this forum for a few days. that dosnt mean that i dont care about your problem. this is a forum of great guys, try to be a bit more patient about it.

Yeah i wasnt sure if it was just cause i was not known or something an that was the reason i wasnt gettin replys i totally understand ya 89 - i will do the things ya told me - an while i am at it i am gonna check the MAF cause it could be dirty or oily something cloggin it up or something .... but that might be what it is too - if i unplug it an it starts an then plug it back in an it doesnt that would mean its bad right or would i have to take it off instead of just unplugging it?

Thanks

fuel pressure should be around 40-45psi with the engine off, and no more than 8-10psi drop when the engine starts.

you can try cleaning your MAF sensor. shoot some carb cleaner in there until the tiny thermal wire is shiny again. be careful not to get to close, and dont shoot directly at the wires, they are very fragile.

there is a way to test the MAF sensor, but it's long and complicated and to be honest i dont remember how :smile:

question, are you running a K&N air filter???

Yeah 89 K&N Air filter in orig tpi intake

I know alot of people that use them - is it a bad idea cause i have heard stories of other cars fuckin up pretty bad cause of K&N filters - so i dont really know :dunno:

ok, i deal with this alot at work, not saying its your problem, but people tend to over oil them when they clean them, the excess oil blows off and coats the MAF sensor wire, throwing off the reading, makeing it run like shit, that might be your problem, try cleaning the wire with brake clean or another electronic aerosol cleaner.

yeah- i was wondering if the maf sensor was real dirty myself -just wanted to see if someone else thought it could be the prob too , so i guess that mean just clean it up see how it goes after that .... k thank 89

no prob man.