91 Camaro 305 TBI 5.0

Guys i am seriously tired of this issue..and this is just another desperate attempt to get some help.

Ive tried just about everything that comes to mind and the car still surges on start up and hesitates while i accelerating..


When i start the car it starts at about 1500 RPM and slowly drops and stays at 1000 RPM.. While driving my rpm is usually at a steady 500.

When im trying to pull out of a parking spot or anything and i put it on reverse the car's idle will drop below 500RPM and try to die but sometimes it surges back up and stays on...other times it will just die.

When the car has been sitting for a while and i start driving ill give the car gas and it will just hesitate bog down and try to die, at times i continuously press down on the gas and its like if im not even giving it gas..its hard to explain but it cancels out the gas..ill be pressing the pedal all the way down to the floor and the car wont move? i have to keep pressing up and down on the pedal for it to pick up a bit and stay on.

My thoughts are that something is messing with my air/fuel ratio?

Heres the list of everything Ive thrown at it.


-New IAC

-Distributor cap & rotor

-Fuel Filter

-Oil filter

-Air filter

-PCV Valve

-Bosch super copper spark plugs (3 days ago)

-Bosch Spark Plug wires (3 days ago)

-Full TBI gasket rebuild (took the whole thing apart replaced all
gaskets/regulator diaphragm)

-Checked injectors (perfect spray pattern)

-Removed the diverter valve/air tubes.(diagnostic told me it was faulty pumping constant air into system)helped some not much..

-New Starter

-New ignition Coil

-New o2 Sensor


Things i haven't changed an or am thinking of changing since researching forums..

-Map sensor
-CTS (Not sure where its located)
-ATS (Not sure where its located)
-EGR Valve
-Alternator
-Fuel Pump
-Fuel Regulator
-TPS


I need some advice on what to do, Ive been depressed about this because ive already dumped so much cash into parts and this is still an ongoing issue. I dont have any fancy tools or anything like that and only basic knowledge of vehicles.. so im depending on some opinions and researching, as far as pressure testing and volt testing i don't have any of that available to me at the moment.

Basically am just a 20 yr old student with a garage a couple of wrenches some ratchets and a third gen.


This is my last attempt at fixing this myself, im planning on going to buy the two temp sensors tomorrow hoping that maybe just maybe these two little 10 dollar sensors will fix this issue that ive already spent so much money on.

I need some advice and opinions on what to do and what it could be/or sounds like?

Thanks for reading

 

I know it's a bit late because you've already spent the big bucks but stop buying parts until you know what's wrong. You either need to take it to a shop or someone that's knows how to diagnose the problem properly or you need to buy some basic equipment and learn yourself. It's an extra pain if you need to keep using the car. The problem could be one thing or several things together. You can do a lot with a decent vacuum gauge, compression tester, fuel pressure gauge and digital volt meter. If you've got a Chilton manual it covers a lot about diagnostic testing of the various components and how to read and interpret the fault codes.
Without more test results it's hard to say but off hand it sounds like a vacuum leak. Check all the vac hoses and then maybe block off unnecessry sources of leaks like the brake booster, AIR pump, and egr tube unless you're positive it's not stuck open.
But really you need at least the equipment described and learn how to use it. It's cheaper than what you've already spent.
Good Luck.

 

look up the troubleshooting procedure to check your EGR valve... I think if you apply vacuum it should stumble, if nothing happens then it's either a bad egr or bad egr solenoid...

 

Is the "Check engine light" on? I would find someone with a scann tool that knows what they are doing. Check the MAP/MAF sensor, watch you IAC counts, look at your fuel trims, etc. Also like the previous person said, make sure you do not have any vacuum leaks. Check the back side of the intake manifold. Spray some intake cleaner at the back of the intake when the engine is running, if the RPMS go up you have a leak. Also double check you ignition timing.

 

starting fluid also works when checking for vacuum leaks

 

@knblazer
Ive tried squeezing the EGR Valve and the car does react to it, although i do have to press pretty hard to get that thing to work, so i don't know.

This morning i figured i would take a video of my problem and here it is.
As you can see the car starts warming up at 1500RPM once it gets to 1000RPM it starts stumbling until finally it turns off.


http://www.youtube.com/watch?v=8ZmkYLp_GDQ

@unpredictable

Ive actually searched for vaccum leaks in the past and found about 3 cracked hoses i havent found any others so i think this issue is past vaccum leaks.

The check engine light does come on, but only after the car stumbles and dies.

How can i double check the ignition timing? Ive read on the forums that there's a way to reset it but some people advise against because of a loss in power?

 

Did you adjust the IAC or just slap it in there? You need a voltmeter!

 

i adjusted the IAC spring to the measurement in the haynes manual but thats about it

 

Few questions..

Yesterday i removed the air tubes from my system however i have yet to remove the air pump pulley, could the pulley being there cause me problems? I have the custom belt and everything ready to remove it but i havent got to it yet. I had this same problem before i removed the air tubes and diverter valve but it seems to have gotten worse after i took the tubes out yesterday.

About the volt meter im thinking about going to get one atm, but what would i test with it?

 

With a digital volt meter (dvm) you can test wiring to see what's hot or grounded and measure voltages. You can measure resistance to see if a wire has a break somewhere or indentify which wire at one end of a loom matches which wire at the other end and you can measure the resistance of injectors. Plus if you follow the appropriate instructions you can test all sorts of switches, relays, sensors etc. But you also need a vacuum gauge. Recheck any possible way other than the throttle body that air could get into the intake. You have to eliminate them as problem sources then you can test other factors. When you replaces the IAC did you make sure all the air passages were clean? You may have to remove the throttle body and make sure it's all clean and clear or the IAC won't function correctly.

 

yeah im pretty positive that the tb is clean, i actually removed it all and cleaned off all the grease when i replaced all the gaskets.

Update: I went to a local shop by my house and got my timing reset to stock settings so far the car hasnt died on me yet however i still feel a tiny bit of hesitation when accelerating.

Will update soon in case i run into the same issues.

Who cares right? it will be just another 25 bucks down the drain.. worth a try.

I still want to get that voltmeter it seems like it will benefit me in the long run, any specific wires i should test?

 

I didnt see you mention the TPS (Throttle position sensor). With a voltmeter, or multimeter you can test this. The procedure for testing/adjusting it is in these boards. I bought my '86 IROC with the exact same problem you are describing with your car. I put a new tps in it and it ran fine after that. Let me guess: If you "Ease" into the throttle very slowly it will accelerate, but if you floor it, it will want to die?
Hope this helps!

 

forgive me if you have answered this, but i saw you said the SES light comes on after the car stumbles and dies, Did it throw codes? a code would really help determine what is causing problems

 

@caveman
the last code i got was a code 44. But this was a while back.

@Drknow im gonna check that out im off to get a volt meter so i can get readings.
Yeah its something like that

Stay tuned

 

ok, i was just thinking your video looks exactly like what my car would do when i got it, My dad and I replaced everything you have, and even the stuff you have not gotten to because of different codes that would pop up(my car was in need of it all anyway so we looked at it as an investment)

anyway, it turned out i just needed a new ECM, my car never threw a bad prom or bad ecm code, but changing he ecm to a reman unit and putting my stock chip in it solved my problem

 

That would really suck if i need a new ECM..
thats a couple of big bucks just in buying that thing isnt it?

Updatei just got back from buying a multimeter and i now need to know what exactly to test and how to do it im kinda new to all of this but im willing to learn if someone has the time to explain it to me.

Car hasn't died since i got the timing reset this morning to 0 degrees..however there is still a bit of hesitation when i accelerate.

 

i paid $75, but you have to give them the core

but definitely test anything you can before concluding you need to buy the computer

 

How old is your cat?? I would try lookin at that

 

The timing shouldn't be 0. Should be 6 degrees before TDC? Read the diagnostic sections of the manual. It tells you how to do a lot of testing. You could start with the map sensor which is vacuum controlled and the TPS. Just do lots of reading. And search the forum and google because someone somewhere has done it and written detailed instructions. Don't forget the vacuum. It must be predictable before you can reliably diagnose anything else. The Mighty Vac is good. It's also a vacuum pump so it can be used for some sensor (eg map) testing and brake bleeding.

 

Take it back to the shop and have it set to factory spec's.

 

Aside from the good advice youre already getting here, you should really check fuel pressure. also, test your O2 sensor by simply unplugging it and running the engine. If the engine runs okay with the sensor unplugged, replace the sensor.

 

Well we got the timing to 0 because the hood sticker said the timing for automatics was 0 degrees. Right next to where it said the Spark plug gap size of 0.35.

What do you mean before TDC?
Im not sure why they would put the wrong thing on the sticker?

I just got home from work and am ready to start testing sensors etc.
As far as the cat being old it probably is ..the guy that sold me the car said it had no cat but i can clearly see the cat under the car..so who knows.

UPDATE
The car is still dying on me..Its gotten worse.. it now dies on me while im driving.. It died in the middle of an intersection today..and man was that embarrassing.

I need to find out exactly what to test for voltage and an idea of how exactly to do it. Whats a normal/bad reading?

To make things worse my Speedometer just stopped working out of the blue. it had done it before but all of a sudden it just started working again.. all i can hope for is that the speedo comes back :[

 

Before TDC, is Before Top Dead Center, when you set your timing(or have it set) they have to disconnect the EST bypass(brown) wire on the pass side up of the engine compartment,

your timing varys on motor, if you have a 305 TBI i can say for sure your timing SHOULD be 0 for factory specs, 305 tpi idk, and 350 tpi i know is 6 degrees

best thing to do to figure out the way to test your parts is do a search on this board for lets say "how to test TPS" you should get a ton of threads with how to test a throttle position sensor, do that for everything you want to test(theres even a test for the ECM but i dont remember it)

 

Yeah i have a stock 305 TBI, so im correct with the 0 degrees then? yeah the mechanic at the shop disconnected that wire on the passenger side.
Got a bit scared for a sec there.

Im gonna try searching that TPS info see if i come up with anything.

 

yup, then 0 is what you should be at for stock

 

I adjusted my idle speed and my minimum idle air rate on my 88 GTA L98 last week. I did it wrong the first time, and it ran exactly how you are describing your car to be. I started it up, and put her in reverse to go home and it almost died on me, and hessitated. I dont know much about TBI, as my car is TPI. But if it has a TPS, it must have an idle set screw, and if it has a computer and an IAC you would have to set the minimum idle air rate. On my TPI to set the idle air rate you need to put the computer in diagnostic mode where it flashes the trouble codes and let it sit there like that for 30 secs at least. Then you unplug the IAC, and start up the car. When you start the car you adjust the idle set screw to idle at about 450-500 RPMS in gear when warm. You then turn off the car, reconnect the the IAC, and set the TPS to .54 to .56 volts. If your TPS has 3 wires coming out of it, you want to stick the negative prong of the voltmeter in the top wire connector, and the positive in the middle wire. Then after you adjust the TPS, you need to drive the car for abit over 40 MPH because that's when the computer resets the IAC to specs. If you do all of this to your car I would be willing to bet it would solve your problems. If no SES light is coming on, especially. Once again I just described the way to do it on a TPI car, not a TBI. I cant imagine a TBI would be much different, if it is, someone on this forum please tell him whats different. Look in your haynes manual for your car if you have one, it will tell you how to do it for TBI.

 

@bigbadgta
Im gonna give that a shot, how exactly do i adjust the voltage on the tps though? do i have to tighten it or something?

And the voltmeter should be set to dcv right?

 

I just got the computer into diagnostic mode and got the following codes

Code 22 = Throttle position sensor Sticking or misadjusted TPS; poor electrical connection, Open or short in circuit; defective TPS;Defective ECM

Code 42 = Poor electrical connection, open or short in circuit; defective ignition module; defective ECM

and of course code 12 but that's just diagnostic mode correct?

What are my options? about code 22, im gonna head over to my local autoparts and get me a TPS to get that possibility out of the way.. im also considering getting the ignition module, hopefully these 2 will help me out.


Thoughts and opinions? apparently those of you who said it was the TPS were correct since im getting that code.. now im hoping that new TPS comes pre adjusted? or will i have to adjusted myself?

Also hoping its not a defective ECM..

 

Now that you have your volt meter you could use it to test the TPS before buying a new one. Remember the point is to only buy stuff that doesn't work. The code could indicate the TPS just wasn't adjusted correctly not actually defective. To bench test you'll need a +5 volt reference voltage to apply to the TPS. That's what comes from the ecu. I use the output from a USB port on my computer. Get a USB cable and open up the end so you've got a +5v wire and a ground wire. You can use your dvm to tell which is which. Then connect the 5v wire to the appropriate TPS connector and measure the output voltage as you move the TPS. You should see a smooth change in the output voltage. I don't know the actual voltages at each position but do some searches (board and bing) and you should find detailed instructions. As for the ignition module make sure the spark advance wire was reconnected. Also unplug stuff and make sure all the connectors are clean. Sometimes just unplugging and plugging back in can clean off oxide and make a good connection. Good Luck and keep reading.

 

hey bigbadgta, im about to try ur suggestion.. i understood everything but the part about changing the voltage on the TPS, how exactly do i change the voltage? and what should my multimeter be set to? it has all sorts of settings like DCV 10 megaohm, ohms, dc10a, Dcma, battery load test in 1.5v, 6v, 9v, 2v, Ac MA etc..

 

Sorry I didn't answer you until now, once again I am not familiar with TBI vehicles. I don't really think that the TPS would be much different though they all do the same job. In order to adjust my TPS I just loosened the two torx bolts that held it onto the throttle body and moved it to spec. The way a TPS works is that there is a lever that is connected to the throttle body that is pushed down when you touch the pedal and there for tells the ECM what the throttle position is with voltage readings. The TPS voltage changes when you touch the throttle, when you touch the gas the TPS voltage rises, and when you let off the pedal it should fall back to idle at .54-.56 volts. Therefore, when you adjust the idle set screw it raises the TPS above idle voltage and screws with the way the engine runs. I know when I was done screwing with my idle speed, my TPS read about 70 volts, so I had to loosen the screws and turn it until it was back at .55 volts. Just remember when you are doing this procedure, whenever you adjust the idle speed you need to put the ECM in diagnostic mode for 30 secs first and disconnect the IAC so the computer sets the minimum idle air rate for your idle speed.If you go ahead ind just change idle without doing the steps right, the car will not idle correctly. If your car already idles at 450 RPM in gear, just put the computer in the diagnostic mode for 30 secs, disconnect the IAC, let it run for a min and then turn off the engine. Dont touch the idle screw, just make sure the TPS is set correctly and reconnect the IAC. Take it for a drive and see if its fixed. I am sorry I cant explain it better, I just learned how to do this myself about 2 weeks ago. If you have a haynes manual, I would look up this stuff in there before I touched the car just to be sure. If you don't have one, I can look in mine tomorrow when I get home from school to make sure the procedure is the same. Its 12:30 AM right now and I have to get up at 6 to go to school so I have to go to bed lol.

So to recap

Put the computer in diagnostic mode for atleast 30 seconds
After 30 secs, disconnect the IAC
turn on the engine
Set the idle screw so the car idles at about 450-500 RPMs in gear while warm
turn off the engine
reconnect the IAC
Set the TPS by loosening the bolts, and moving it till you get it to spec.
start the engine and take it for a drive.

If your car already idles at the right speed do the above, just do not **** with the idle set screw, just make sure the TPS is to spec.


Oh and for the multimeter, I believe it should be set in DC section, and on screen find the one that reads 0.00 before you read anything.

 

How's it coming on this? I know you've had a lot of suggestions but I would go to a jy and snag a MAP sensor, I blew a ton of money on my 89 305 tbi searching down this problem, it just bucks and bogs like you're not getting the proper fuell right? I replace my entire fuel system and it ended up being my MAP, get your TPS dialed in right and then go from there, if it hasn't improved go for your map sensor, I say JY because they're pretty pricey new and easy to pocket at the yards, worst case scenario if thyat isn't it it didn't cost you much or anything if you can sneak it out

Oh and for your dvom set it to the 20 on the dcv area, you've have to manually range them and 20 is your best option for anything 12v and under

 

The 91 does not have an adjustable TPS. The most likely cause of your symptom is either vacuum leak, low fuel pressure, faulty CTS, dirty injectors, or a defective MAP sensor. I would not go one step further without first verifying 9-13 PSI fuel pressure. Closer to 13 is better. Its common for the regulator spring to break, causing pressure to drop off.

 

Okay guys heres the latest update.

The car was pretty much undriveable for the whole day.. died on me continiously over and over..I took it to my friends shop and he said the fuel pressure was below the norm. I just got back from the shop only (was at work all day) to find my rear end dropped ..fuel tank out on the ground and my back tires all over the place..

So now i guess im in for a fuel pump, is there any specific i should buy? Id like for the car to be ready ASAP and if i can pick one up from any local autopart stores suggestions would be great.

Im crossing my fingers that its the pump and not the actual regulator or ima be pissed.

 

Hmm, Theyre replacing your fuel pump for low pressure? Did they perform a dead head pressure test to verify it was the pump? Did they flow test it to verify sufficient volume? Youre not going to like hearing this but aside from failing one or both of these tests, low pressure is rairly caused by the pump. Especially low pressure at idle, where pressure is generally first tested.

As I said, it is common for the regulator spring to break, causing a drop in pressure. Its so easy to disassemble the TBI to check the spring. It takes a few minutes and one gasket at reassembly. Sorry bro. BTW, a good aftermarket pump is Bosch dual stage or AC Delco.