Alright here's the deal...

For quite a while now my car has had the issue of running rough for a few seconds immediately after being started cold (after it's sat overnight)

I've done everything I know how to diagnose this problem and I've run out of ideas...

Ive replaced:

Plugs.
Dist. Cap.
Rotary Button.
Injectors (Done a little while back)
IAC Valve
Fuel Filter (Done less than 6k miles ago)
Wires (Done a while back, ACCEL 8.8)
Coil (Done a while back, MSD)

My cold start injector isn't at fault because i've physically taken it outta the manifold while still hooked up to the fuel line, primed the fuel system, and watched as it didn't leak a drop... I've even unhooked it and started the vehicle and it still runs rough for a sec or two...

I've tried and failed to reset the IAC valve via the instructions on this site because I can never get the engine to immediately fire back up after putting it through diagnostics mode...

I'm also unsure if the TPS has anything to do with it, but if it were the culprit, wouldn't it cause it to run bad all the time?

After those few seconds of running rough on cold start up, the car has absolutely no problems after that... it will fire up strong and fast even while warmed up...

I took this video today in hopes it would help... If anyone has ANY ideas please let me hear them, i appreciate any feedback towards the issue....

Thank You

 

nice gta, nice clean body. you mentiond the tps but you didnt mention if you adjusted it. i would check to make sure the middle wire is reading .54v ignition on. if its .075 volts off of that you could have a problem. since the ecm doesnt know its idling and the iac valve wont function as it should.

 

I have not adjusted it, mainly because I don't know how too Nor do I have any way of measuring the voltage...

My question still stands though... If the TPS was to have any part in being the problem, then why doesn't it run rough ALL the time at idle...Why is it only on cold start up?

 

well these ecms arnt to bright to begin with they are quite primative... and usually the car can idle smoothly when its slightly warm it doesnt take much heat for them to idle well. cars struggle to idle when they are colder.. also when you are cranking the engine over the car doesnt always fire on the first spark. so some cylinders well be too wet to create a proper explosion. your car should be idling around 900-1000 when the car is cold until it heats up i believe. so i would recommend picking up a multimeter they are like 20$, id get a better one if i was you its a GOOD tool to have around especially for wiring.

theres good tutorials on adjust tps on the home page under tech articles

 

Hmm... now that i think about it, my TPS is probably the only thing i've never actually replaced or touched myself... I guess it only makes sense to have it checked out by someone who knows what they're doin or just learn to do it myself lol...
Thanks for the help.

Anyone else have any other ideas? Or does the TPS sound like only the issue here?

 

id recommend doing it your self its a easy thing to do, and a good thing to know

 

Alright,

I set my IAC valve (correctly) and ended up at around 700rpm at idle... I've also been battling the issue of slightly surging idle while at operating temps. This seems to have fixed it... *knocks on wood*

I then read up on how to set the TPS and borrowed a multimeter... With the ignition in the ON position, I was getting a reading of .40

I made the adjustments to where it was reading .54 at rest, and made sure it was above 4.0 at WOT...

I immediately noticed a nice increase in throttle response (i already had awesome throttle response before)

Now the true test is gonna be when i start it up tomorrow morning and find out if my adjustments made any difference or not...

 

well whether or not it fixes it at least you have now eliminated two possibilities

 

well.... now it's even worse off than before.....

Now when it starts up from sitting overnight the car runs even rougher and now DIES a couple seconds later..



I don't know what the heck to do.... It turned out that my IAC valve had completely seized up, so I bought a new one and set it.....

WHY is my car doing this on cold startups?? Surely someone out there has some other hints...

 

i had a simaliar problem for cold starts turned out to be a fuel pump issue and a MAF issue but i havent seen a mention of a check engine light so.....check ur fuel presure, if u aren't getting enough presure at start up or your getting too much presure that could cause the issue your discribing

 

No engine codes to speak of... Car runs like a champ 10 seconds after cold start up, it just runs really rough like it does in the video above.

Fuel Pressure Regulator? Hell i don't know...

 

shoot yours starts up way better than mine. mine is much worse. i have to stay outside for a few minutes and then go inside and because its loud enough i can hear it inside and have to go to the window just to make sure its running. dont know how to help if mine runs worse than that. ive also replaced a lot of things over the years to get mine to be like a brand new car that you turn the key and its gauranteed to fire the first turn of the key and stay running. better than it was but still not there.