hard to start when warm

i have a 99 GT and i am having problems starting the car when the engine is warm. there is no problem starting when its cold. but if i go to start it when its already warm, it will start then shut off. sometimes if i get lucky it will stay started but idle will jump up and down, like its going to stall. idk what to check. i already replaced the IAC valve so that cant be it. im stuck.

Does it seem to take longer to start when its warm? cranks longer then starts then stalls?

Check the pressure regulator and make sure it is not leaking.

Unplug the MAF and see if it starts easier.

okay well its starting to get worse. when i go to start the car it turns over for a couple of seconds then finally starts. and sometimes it even shuts off after it starts. but if i push the gas pedal or put it in gear, it will stay running. does this sound like a bad fuel pump? what are other symptoms i should look for for a bad pump?

if your idle is jumping up and down and then shuts off, check your Oxygen sensor.

sorry for some reason it did not allow me to edit my previous post, but just wanted to tell you that in this case you will not have any codes. I am 100% sure :iceslolanthat if you replace O2 you will be :smile:

yeah im not getting a check engine light or anything. so your saying that if i replace an O2 sensor it will fix this? yeah but which one?

I wouldnt go wasting you money on an O2 sensor just yet! :grinno:

How old is your air filter and fuel filter ??

I'd also check your engine grounds, and the ignition system connections. How old are you plugs and wires ?

When was the last time you cleaned your TB and IAC ?

Check what Xero said but if you never replaced your O2 before and you have more than 60K replace it anyway. So you need the AF 02 sensor. Right behind your cylinder #3 on the exhaust pipe. You will need the special socket. Sensor is $58 at Auto zone (Bosh).

Xero I think that if it was the grounds he would have the problems all the time not just when the engine is warm. IAC was replaced from what I understood. I still say AF 02 replace it and get it over with :iceslolan.

yeah im not getting a check engine light or anything. so your saying that if i replace an O2 sensor it will fix this? yeah but which one?

Just to double check disconnect your AF 02 when you try to start it next time with warm engine, if you don't have the same problem then you know it is AF O2 repeat this 2-3 times just to be sure. I wanted to edit my previous reply but it is not working.

How about testing the O2 sensor (http://www.automotiveforums.com/vbulletin/showthread.php?t=672110)to see if its bad before wasting money on it.

My 99 SE had 198000 miles on both and worked fine up untill that point. :confused:

well my air and fuel filters are only a couple months old. and yes i already stated in one of my first posts that i replaced the IAC and cleaned the airways.

it is called an OXYGEN SENSOR,!!!:shakehead obviously you don't have much skills or experience to do it yourself, so just take it to a shop and pay 5 times more:grinyes:

hey asshole. dont tell me that i dont have much experience. i was answering XERO's questions because he asked if I changed the air and fuel filters. i am not getting any hesitation or anything relating to a bad oxygen sensor. no service engine light either. so i dont see why i should go and replace them.

You probably used a lot of injector cleaners, upper intake cleaners etc, if you connect your car to good scanner you will notice that your cross count is higher than necessary about 13 and it should be about 4-5 for GA 3.1 that is where the problem is, I told you how to check disconnect it and drive your car for one day with disconnected sensor and come back here and tell me what happened Ok....

go on junk yard they remove 3-4 sensors they will usually give them to you for free, try one or two and see the difference, if you do not see difference come back here and say that I was wrong

mjtr21 watch the name calling.
3100, those posts were uncalled for and unnecessary !! :disappoin

We're here to solve probelms not make more.

It could be many things or nothing , even a dirty MAF can cause such anomalies.

Also 3100 the OP's engine is a 3.4 not a 3.1.

I will take the heat, it was my fault, I even wanted to delete that post but I couldn't. So did deserve a response from him like that, but I had to fire back.
And it :headshake happen again I promise....
But I was :mad: because he ignored my suggestions when I told him to try disconnecting the O2 and drive it for one day just to see if that repeats. You right MAF most of the time will not show you code unless it is really bad and pcm senses 3 consecutive faults in 3 consecutive bad trips in which engine was fully warmed up and fully cooed down for each new start up or it will cancell its counts and will start over until this 3 final consecutive faults finally happen, in other words he can wait for this code months and months. GM's valid MAF test is to start the engine and tap the top of the MAF sensor with the handle of a screwdriwer and listen for engine rpm change, if the rpm changes replace your MAF. Also if it was MAF engine would choke for a sec every time you press gas pedal if the trans is in D. And just because I am new on this forum does't mean that I just started to learn about cars and on the contrary 3.1 and 3.4 I know into very little details almost by heart. Once again sorry mjtr21. -3100

yeah im sorry for the name calling. i just took offense because i had lots of things going through my head and just put whatever came up. well i havent had the time for checking the O2 sensors yet. but i cleaned the MAF sensor before. and i tried that tapping thing while it idles and there were no changes so im guessing its good. but when ever i get the chance i will try that. thanks for the suggestions.

oh yeah i forgot something else too. whenever i start that car and it feels like its going to stall, if i put the transmission in gear it stays running.

Is it possible for a vacuum leak to cause this problem?

i did not see a reply to the fuel pressure regulator post but in this situation it sounds highly possible you may not be able to see visible leakage but it will bleed fuel into intake after your first drive then when you come back it will be flooded the easiest way to check is with a vacuum pump. apply vacumm with vehichle running if no idle change regulator is bad. email me if you need any other advise. you may have maf or map sensor problems but the fp regulator is the most common and also the cheapest to replace

oh yeah i forgot something else too. whenever i start that car and it feels like its going to stall, if i put the transmission in gear it stays running.

That does sound like a weak/bad injector. If one is bad when it gets hot the coil inside doesnt work properly.

Another way to see if the fuel pressure reg. is bad is remove the vacum line you would see/smell fuel from the hose. You could also smell gas thru your HVAC if fuel gets into the vacuum system. :2cents:

okay well i finally made it to the parts store and bought another FPR. im putting that in today when i get the chance. i also think i need another fuel pump. reason being because it sounds kinda loud, and my gas gauge doesnt work right. does anyone recommend a certain brand for what to get? or should i just stick with OEM?

On the fuel pump, just use an OEM, if not it will fail sooner than later.

okay well i finally made it to the parts store and bought another FPR. im putting that in today when i get the chance. i also think i need another fuel pump. reason being because it sounds kinda loud, and my gas gauge doesnt work right. does anyone recommend a certain brand for what to get? or should i just stick with OEM?

The fuel pumps come two ways.
One is the entire module with a new level float and pump, for around $320.
The other option is to just replace the pump(and you can buy just the level sending unit seperate) much cheaper but if you buy a cheap pump it wont last long. :2cents:

okay well as soon as i get the money i am goin to replace the fuel pump assembly. also another question. i was repalcing the FPR earlier today and i broke that vacuum line that connects to the front of the upper intake manifold. its a wierd off-white color. where does this lead to?

on older models the vacuum port on the front of the upper plenum goes to the vacuum modulator and AC control. However you do not have modulator so it could be going to ac only. See if you have AC now. on the back of the upper plenum one port is capped (near the alternator) and the other port of the same size is for your MAP (T) connector which also connects to your FPR.

did you ever try that thing with o2?

Or the best thing is to look under your hood for your emissions sticker, it should have a good vacuum diagram for your engine.

no i havent gotten to the O2 sensor yet. right now im busy with trying to get the damn rear defrost to work. and i will not give up until its fixed lol. ill check under the hood again for that sticker.

So what was the end result? My 01 grand am is doing the same thing. I changed out the MAF sensor and the pcv valve and the sporradic idling stopped but the car still has a hard start and stumbles when its warm.I added new plugs and wires checked the spark on the coil. Now im geting ready to change out the fuel filter and unplug the oxygen sensor like suggested. If that fails then I am going after the fuel injectors. can you guys save me the trouble and money and tell me what fixed the problem

My 01 grand am with 4.3 was doing the exact thing at first I got a p0305 code then after changing aout several parts i got a p0300 code and it was geting worse. the car would have a hard start when warm and the idle was rough and would go up and down till it stalled after running the car I would get a strong exhaust smell. It turned out to be the fuel pressure regulator. the vacum hose on the top would suck fuel in and ould burn in the intake which caused all the trouble. Now the car is running smooth hope this Info helps.

okay well i unplugged the maf and when i started the car it doesnt stall out. so im guessing my maf is bad.