I have a 1991 Camaro RS 305 TBI. I currently rebuilt the entire engine the past two months. I just dropped it back into the car this weekend and I'm experiencing a problem. I've looked for the answer for quite awile and it seems some other people have had the same problems but no solution.

The problem
I tried starting my engine and while giving it some gas, it came to life. I kept it running at about 2500rpm for around 20 mins. As soon as I tried to let it idle down it died. I can not start it without feathering the gas. It runs very rich and the rpm's surge up and down even though I am holding the throttle at a steady spot. After a bit, my check engine light came on with Code 33. (Low intake manifold vacuum) As soon as the check engine light came on, the engine cleared up. I hear a higher suction noise like more air is entering the engine. I looked at the injectors, and they aren't letting near as much fuel in. The engine then idles fine without any surging or anything.

If I then hold the throttle back up to 2000rpms for a minute, the light goes out and the fuel starts dumping again and dies the minute I try to let it idle back down again.

I replaced my MAP sensor and that didn't do anything. I have a new oxygen sensor on it as well.

I don't know if this is another sensor that my computer just isn't picking up or what. I kind of ruled out fuel pump and all that because of how it runs fine if the engine reads code 33. I believe when the light comes on, the computer stops reading from sensors and goes off of pre-set information.

Any help would be great, this problem has definitely stumped me.

Thanks,
Wyatt

 

if the egr valve is stuck open it can cause that. something else you may want to look at is the distributor pickup coil and see if its rusty. check timing and fuel pressure. timing=0 with timing connector unplugged, fuel pressure=13psi

 

I have timed it to the best of my abilitly. It is really hard to when it won't idle. I don't believe it has to do with the egr either because of the fact that it seems to run fine after the check engine light comes on with code 33. I attached a vacuum gauge to the manifold and im getting about 8 psi around 1000-1500 rpms. When the engine light comes on and the engine smooths out a bit, the vacuum increases about 2-3 psi. I installed a performer rpm edelbrock cam when I was rebuilding the engine if that might have something to do with it.

 

that cam probably make a little less vacuum than stock

 

That is what I think as well. It is giving me around 10 inches of vacuum. Does anyone know what the stock vacuum should be? How can I modify my MAP Sensor/computer to say the low vacuum is alright so it doesn't run so rich thinking the engine is under load?

 

stock vacuum is around 15 or more. you'll need to burn a chip. i'm not familiar with that but there is info here on that subject.

 

Thanks for the information. I really think this is the problem. I'll look into burning chips.

 

I have the same issue took it to a shop they told me my TBI seal was bad it's a 5 dollar seal easy to replace they said that why my engine is rough idling making a howling noise from the Intake and surging...worth a shot I'm trying it this week they said it's the guaranteed fix..they said it's a clear sign because of the bad aide fuel mixture a rich exhaust smell

 

Thanks for the suggestion. I don't believe that is my case though. I used the rubber hose trick to find any vacuum leaks and I don't hear anything besides the air going into the throttle body. I believe my problem is that I purchase a bigger cam and that lowered my vacuum in my manifold. My MAP sensor is sensing this and sending a higher than normal voltage to the ECM. The ECM is reading this high voltage as the car is under load (because your vacuum drops when you slam on the gas pedal or just accelerating in general). So i need to reprogram my ECM or get a MAP that would work. My fix and it seems to work so far, I put a potentiometer (pot) across the wire sending signal to the computer. I turned down the voltage until it idled correctly and didn't affect the power when I hit on it. Once I found the correct spot, I read the ohms across the pot and it came out to be about 21.6k ohms. I went to radioshack and bought a pack of 5 22k ohms for $.99. I soldered one of these in line with the wire and everything seems to be working pretty good. This is a decent fix until i reprogram my computer. I wish my problem was a mere gasket leak, but i just rebuilt the engine so it has all new throttle body gaskets Thanks again though