My gta runs terribly when it is first started in the morning. It sometimes stalls on the first start if I don't tap the throttle to help, but this doesnt happen all the time. The major problem is when I put it in gear and drive the car right after I start it. It bucks and hesitates like crazy below 1500 rpms. The rpms drop and it almost stalls, then it seems to 'catch' itself and I take off. After it warms up, the problem is gone. Also if I let the car idle for about 5-10mins before I drive it in the morning it drives fine. I can rev it in park without the hesitation. Any ideas where to look?

 

ttt

 

Have you seen any scans when it's running under those conditions? I'll bet you're running lean, which causes the cool engine, low RPM stumble you explain. Main culprit would be the cold start injector I would have to think.

If it's running overly rich, I would say bad coolant temp sensor or EGR, perhaps even just something more simple like plugs/wires...

Need more info...

 

Unfortunately I dont have a scanner But I do know that it is seems to be happening in open loop. As soon as it reaches about 120degs (according to the gauge) and when the idle drops the hesitation is gone. I also believe it is running lean because I can sometimes hear it popping thru the intake when it is stumbling. Plugs are a couple weeks old and the wires, cap, coil, fuel filter are 1yr old. TPS is at .49v and I cleaned the IAC passageways. I have no stored codes. How do I check the CSI? Could a bad CTS make it run lean?

 

Have you had any luck with this yet? You described my problem to a tee (89 IROCz 5.7 TPI in my case) so I'm eager to find out what worked (and didn't work) for you.

Matt

 

let your car warm up in the morning like most everybody else does? my car has no cold start injector since i run the stealthram and it does about the same. When I first start it up it'll stall a couple times unless I hit the gas and keep it running. Once it starts warming up it runs better. But until it heats up to full temp and gets into closed loop it'll pop and want to backfire.

 

It ended up being a bad CTS. They're really cheap and takes <5mins to install. Hope that helps.

 

heck yah my camaro does the exact thing you guys are listing. it runs great once warm but when cold it will pop thru the intake and hesitate real bad, sometimes bad enough to spin the tires once it finally catches up with itself lol. i know it runs lean but i couldnt figure out why. i'll check my CTS and maybe just put one in for the heck of it thanks for the helpful info guys!

 

what is a CTS? i am a beginner with feul injection... also my car is doing the same exact thing so i may look into changing this.

 

CTS = Coolant Temp Sensor.

 

thanx alot man lol thats what i thought it ment i have been planning on changing it.... i have had to change them in like a million chevy trucks with 350s with tbi and it was almost alwase the problem... it seems like i have the same problem it stumbles a bit till its warmed up then it runs fine ounce its warmed up.

 

well i have the same problem as you guys do as stated above and i put a new CTS in yesterday and it did not fix my problem at all.

this is a long shot but is my combination too radical to run off the programming in the stock chip when the engine is cold? it runs good once the engine warms up.

also how long does the cold start injector fire? i thought it only fired upon startup, but maybe it pulses untill the engine warms up a bit. can anyone clear this up for me?

 

Did the problem start after you did your plenum and runners. You could have an intake leak. While the cars in open loop i treads from the CTS no the O2, so after it warms the O2 kicks in tells the ECM your running lean and tries to richen the mixture, this is why with a small intake leak the car will run better warm than cold, but usually always lean to some extent.

Cold start injector fires on startup and runs for about 8 seconds from what I understand.

 

thanks for the reply. when i rebuilt it 2 years ago it started doin this. but i only drive the car in the summer and it only does it for like 2 minutes when i start it up dead cold so i put up with it. now after my head swap and all it still does it, i have no idea what the deal is, i am almost positive i dont have an intake leak, the car runs too good once it warms up to have a vaccum leak like that i would think. but i am still pretty much lost as to why it does it.

 

where is the CTS located & how can I identifie it?
Im installing a new water pump an a set of UD Pulleys tomorrow.
Its the perfect time to look into this since my car does the same at startup.

 

its a little sensor that screws in to the intake right infront of the throttle opening underneathe the air inatake... if u are replacing the water pump it will be very easy to replace cause its right there...you can miss it

 

i have the same problem now, i have replaced a plethra of parts, and i have narrowed my problem down to the TCC sticking, possibly due to the TPS,

 

how can the converter be locking up? the converter doesnt even lock up untill the engine reaches operating temp, this cold stumbling problem we are talkin about only happens upon cold startup. i have a stall converter and i can tell you that if the converter was lockin up i would feel it due to my higher stall, so either we have a different problem, or it is not your converter clutch.

 

If your converter locks up at idle, your engine dies.

 

last shot, anyone got any ideas on this, sounds like many of us have this problem.

 

I think you need to look at an intake leak possibility. Being that it started after you did these changes. If its a mild intake leak it will affect it more when cold before the 02 sensor starts sending signals to add fuel. If its not a bad leak I could see the ECM compensating fairly well for the change.

To check this out theres a few methods. All of them contain applying some type of flammable gas around all intake seals. I have heard of people using everything from the Acytelene on there welding tanks to carb cleaner and starting fluid. Basically if you have a leak it will pull in the gases and increase your idle RPMS while the gas is still present.

I would really consider checking this out as a possibility. Fairly easy to do. You can check sensors all day long and find nothing if your intake is leaking.

 

i can promise you that the intake is not leaking. it has done this for 2 summers now and i have had the intake off and back on with new gaskets 2 times and it doest the same thing. i pulled the intake to paint it, and again this spring to put the heads and stuff on and it still does it.

 

Bringing this thread back up as I'm experiencing the same problem.

 

heh, back from the dead I see.

I'll go out on a limb and say that my problem was that I was running the stock tune. I had heads, cam, and intake mods. The engine was making around 300hp and still on the stock tune. In 2006 I put the exact same sensors, distributor, and ecm on my 383 stroker with a custom tune and I've never had the problem since. I think my issue was that the stock tune was just too lean off idle.