Hey guys.

I have a 91 RS 305 Throttle Body Injection that I have been working on for quite a while. I took it from not running at all to driving quite well. Just a few more little things to go... I hope.

Okay, my problem seems to be after it warms up. When I come down to an idle it seems like every so often the engine will shudder a little. The oil pressure gauge drops to about half of what it holds while actually moving. And when the car shudders it comes down even more. It seemed like it was just about to die today. Could there be low compression? Or something with a misfire? Any ideas would be welcome.

I have quite a few new parts in the camaro already so not sure where to go from here.

Thanks again for everyone's help!

 

I know you mentioned stuff in your other thread, so to avoid having this program going into re-runs, what parts have you replaced?

 

Okay, here is a list of what has been replaced.

Distributor, rotor, cap, ICM, wires, plugs.
Coolant Temp Sensor
O2 Sensor
Throttle body unit, including injectors and regulator
Fuel Pump
Fuel Lines
Radiator Cap
Other parts have been replaced, but not relevant to the engine compartment.

I think thats about it. I have soldered resistors under the dash to bypass the key resistor for the VATS system.

 

when you timed it did you set it per instructions by removing the cable or did you just turn the dist and used the light and called it done?

http://www.thirdgen.org/settingtiming

 

The distributor was replaced by a shop so I would guess they did it correctly.

 

really?

why aren't you taking it back to them and asking them to check the timing which should be warranty?

 

Have you flashed for error codes yet?
One thing I would suspect, that you haven't messed with yet, is your Manifold Absolute Pressure (MAP) sensor. It's a small black rectangular piece that's mounted to your firewall or cowl, that has a plug and vacuum hose to it. It can be in different places, but look in the drivers side to center of car area. If the sensor is bad, or has a bad electrical or vacuum hookup/supply, it can cause engine running issues. The MAP sensor monitors differences in manifold vacuum (due to engine load/speed), and it in turn sends a signal to your ECM to control your fuel delivery and ignition timing. If the system is acting up, you should be getting a code 33 or 34, and a crummy performing engine.

 

I did flash it for codes, but just by crossing the wire in the harness under the dash. I didn't come up with any. I don't have a scanner. I could take it into a shop and have them scan it I guess.

The reason I have not taken back to the shop is because I never really got it running well enough to see this problem before they put the distributor in so I don't think they are connected. And it only does it after I have driven the car for 15 min or so. Doesn't do it when the engine is cold.

The MAP sensor I have looked at. I did unplug it and it makes the idle much worse. Should I try replacing that? I don't know if you can tell if its bad just by looking at it.

 

Then it's not likely to be the MAP sensor. The difference between a hot & cold engine is the sensors it runs off in closed loop, to adjust your air/fuel mix. The temperature sensor in the base of your air cleaner, and the 02 sensor are a couple to look at. I should expect you to be getting an error code with those though. When you flashed for codes before, did you at least get a code 12? That one's a given with the engine not running.

 

Yes, I got a code 12, but that was the only one. I will look at the temp sensor on the air filter. It is an aftermarket filter that I did not install so might be something wrong with that. The 02 sensor is brand new. Just put it in a week or so ago. I am also going to replace the catalytic converter in the next month. It just needs some new muffler parts. Gaskets, and some pipe, so going to replace it all at the same time.
Going back to my original question, could this be a compression problem? Or seals or rings problem? Or would it be more consistent?