so a week or so ago i had done some work to my car, didnt touch the motor or anything but now when i start the car it runs really rough and i mean REALLY rough for like 5-10 seconds then it jumps to about 2500rpms and smooths out takes a few minutes for the idle to get back down to about 1000. i had a check engine light that would come on every now and again before this started happening and now it comes on right after the idle goes to 2500 and it stays on. i dont think its a vacume problem, but im no sure what it is, the only thing i did was unhook my battery! oh and when i start it up if i give it gas or anything like that the idle stays rough longer.
Oh and when im driving when i get to around 4500-5000 rpm range it sounds like i have a miss.... any input on this problem would be great, i just wanna get it fixed.

 

bump

 

I'd start by doing a complete tune up, plugs, wires, cap, rotor, & filters.
Remove the tbi unit, throughly clean the tbi & iac passages, get a new tbi gasket.
Test the coolant temp sensor, you need to measure the resistence w/ an ohm meter, the test should be from cold to hot, so you'll need a thremometer, a pan full of water, ohm meter. Google "GM coolant temp. sensor resistence" for the values.
Try to read the codes.

 

a full tune-up is always a good thing . but , i would bet a 6-pak that you have a vacuum problem . spend a little time and replace ALL your vacuum lines . replace one section at a time & any broken plastic fittings . 20+ yr. old vacuum lines will crack & leak . good luck .

 

I would have to recommend that you start by determining the cause of the check engine light. Do this by jumping pins A&B of the 12 pin connector under the dash. A&B are the two pins at the top right of the connector. Then turn the key on and count flashes. Code 12 will be first and each code repeats three times. Then the codes start again. To determine code numbers, long flashes are tens and short flashes are ones. Once you know the code(s) being set in your car's ECM, post them for solutions.

 

i have and the light was for EGR system failure.

 

Use a finger on each hand to lift the EGR valve diaphram. You can reach it through the openings in the underside of the valve. The valve is stuck open, causing both the rough running and the rev up to 2,500. Lifting on the valve should cause it to snap shut. For a long term solution, you will want to remove the valve and carefully clear out the carbon built up in it.

 

hot damn that makes sense, never thought about doing that, i figured the EGR code was because my cat converter has been cut off from previous owner so im running open exhaust. which i know is causing part of my gas millage problems. Thanks for the info, didnt even cross my mind doing that.

 

Cool. As far as the Cat, or lack of it, causing fuel mileage issues, that shouldn't be an issue. On a stock vehicle, the catalytic converter, unless it's clogged, doesn't have much affect on engine performance.

 

ya i know when there clogged it wont run right or at all. my 87s cat was clogged and it wouldnt go faster than like 15mph. But my though with the no exhaust is since there is no back pressure it would effect something. its basically open manifolds

 

with open manifolds the 02 sensor may not be getting hot enough causing a rich condition.

 

thats true

 

So, is it still running rough? Free flowing exhaust won't make run rich enough to make it run rough. Disable the egr by unhooking the vacuum hose to it. The egr being stuck open will not make it rev up, it'll make it run rough at idle or stall.

 

its running alot better after i shut the EGR valve and cleaned it the best i could while it was still on the manifold. its not perfect, so im going to pull it off tomorrow and clean it better, and what will taking the vacuum line off it do?

 

no a free flowing exhaust will not hurt it. but a straight manifold with no exhaust is not going to allow the 02 sensor to heat up correctly.

 

Pull the hose that hooks to the egr valve itself, so it wont open. The solenoid that controls the egr's vacuum supply, it won't know the difference. This is for testing purposes, drive it for a couple days & see how it drives.
Remember when I told you to remove the tbi? Right under the tbi flange (in the 2 bores) you'll see a couple of ports, this is where the egr feeds the engine. when you take off the egr valve itself, blow compressed air into one side of the egr port, it'll either be blowing through the exhaust (you'll hear it at the tail pipes) or at the tbi ports. Both side of the egr flange should free flowing when you blow air in there.

 

ok ill try that out, ive cleaned the IAC and TBI. it seems like its better but still dont have much power. for example i got on the highway after i was done with everything and it was hard to pass people, it would still bog down. not as bad, but its still doing it. i just might go buy a new EGR and MAP sensor. im pretty sure the map sensor is bad so i dont even have it plugged in. When it is plugged in it makes the car miss fire and cut out real bad for a few seconds until the ECM corrects it

 

so does this car have exhaust or open manifolds. did i read this wrong?

 

No exhaust, previous owner cut the catty off and ripped everything out. like a moron. So its open manifolds with the stock pipe up till where the cat was

 

ok. that is what i thought you said. i believe that is going to cause a fueling problem with the 02 sensor. maybe not as bad as you are experiencing. but i would definatly get that fixed. could solve a little of your problem. the 02 sensor needs to get hot. i know that some of these cars are sensitive enough to throw an 02 sensor code with a good set of headers since the 02 sensor did not get hot enough to make it work correctly. wold throw a code after a short drive.

 

i agree with wat your saying because i know alot of cars that are that way, mess with the exhaust a little bit and the light comes on. But im not even throwing an o2 code. Im tryin to sell the car to get a truck. Ive got a guy thats probably going to buy it, but i would rather have everything up to snuff before hand. Ive been forward with everything, havent hid anything. But i would like to fix wat i can get fixed. my luck i would dump a bunch of money into it and he will turn around and swap the motor haha.

 

Back to your MAP sensor. Having the MAP unplugged causes the ECM to run on default fuel since it can't see manifold pressure. When you plug it back in the engine will run rough for a minute, or even stall, as the ECM suddenly switches back to it's normal fuel map. That doesn't mean the sensor is bad. You can test the MAP sensor with a voltmeter to verify if it's okay. The MAP being unplugged would explain your having no power.

 

i get what your saying, didnt think about it causing the loss of power though. but it runs rough with the map sensor plugged in everytime i start it. how do i go about checking it with a voltmeter? the map sensor itself or the plug that goes into the map sensor? i dont see me getting a reading from the actual map sensor though. but idk i have never tested one

 

http://troubleshootmyvehicle.com/gm_...ensor_gm_1.php

really crude but simple.

 

thanks for that thread, think ill keep that site around to for any other future problems one of my vehicals might have

 

Are you shifting manually? The LO3 305 V8 is supposed to max out at just 4000rpm.

 

not shifting manually but it deff dosent max out at 4000. i've had the car in the 6 to 6500rpm range when it was running right with no problems, MAYBE just maybe close to 7, which is pretty stupid on my part and i realize that

 

Yah, that sounds fishy. The TPI cars shift that high, but I don't think the TBI cars are supposed to shift that high in the rpm range. Have you done any after market upgrades?

 

my bad let me refrase that. when im just driving it in regular OD it shifts like its sposed to. i HAVE shifted it manually and got it to those RPMs, i though u ment that there was a rev limiter on it.

 

No. No rev limiter. But the site at leasy says that max HP is at 4 grand. And max tq is at 2400. I have't really looked at my techonmeter, but I'm pretty sure you shouldn't be anywhere beyond 4500rpm.

 

it has been. wether it should be or not, it has been haha. cant take it back now

 

Well at the very least I wouldn't take it there again haha. I know I rev my to about 7grand when standing still, but never while driving. You could throw a rod or something.

 

ya but dry reving it aint much better haha, i've seen my buddies harmonic balencer fly off cause when he was dry reving it in the walmart parking lot

 

I don't really do it that much. And definatly not right after starting it. Or in the Wal-Mart parking lot haha.

 

but i agree, not planning on doing it anymore. last thing i need is to throw a rod.

 

lol man i tell ya what it was pretty funny seeing the look on everyones face standin around watchin that thing just zing across the lot

 

Haha.

 

ok SO. i made an EGR delete block this morning at the shop, hoping it might help some of my problems. it didnt do ****, im to the point where i cant even give it more than a quater throttle with out it stalling and cutting out. it does this when the map sensor is plugged in and unplugged. I dont want to go buy a new one because im still not convinced it is my problem. Any idea guys on what else it might be?

my brother has an intake and carb for a 305 that he neglected to tell me he had and didnt bother to bring it this week when he moved down. im about to just swap them and run a carb.

 

Did you test the fuel pressure?

 

No i have not. but i just put a new fuel pump in 3 months ago, thinking it was why my car wouldnt start. well that wasnt the problem, but i just left it in anyways. So it should be the pump. But where is the check valve for the line is at?

 

Tbi equipped cars usually don't have a port from the factory, see if you can rent or buy a tbi fuel pressure tester from auto zone. It has an adaptor that goes between the feed line fitting & tbi unit.

 

if that isnt the problem is there anything else u could think of? i would automaticly think cat convert, but it doesnt have one. my solutions are just getting shot down one by one

 

tune up vacume lines, EGR

 

Yea vacume lines are messed up, theres a couple not hooked up, but they havent been since ive owned it. tune up when i replaced the fuel pump. and i just put and egr delete block on

 

was the intake gunked up on the inside put your finger in the hole and if you feel any thing pull it off and clean it up

 

i didnt check but i will. my brother has a carb intake off an 85 or 86 305, im pretty sure it will fit with no problems on my 305, am i correct? if so im gonna take the intake and sand blast it at work and get it all cleaned up and put a carb on it.

 

it will work after sand blasting shoot it with a spray bomb rattle job