Ok first off I am pretty much ignorant when it comes to cars or working on them. I have recently purchased a 1985 Corvette Coupe with the automatic transmission. I bought it knowing that it would always need work on one thing or another and that is fine with me. I am currently trying to figure out why the car is stalling out when it has the automatic trans. I've of course stalled out in a manual before (who hasn't?) but never in an auto. It usually occurs about the time after I start it up and then shift into either drive or reverse. I notice that my rpms go down from an initial 1200 to about 640 before it stalls out, though if I gun the engine it will prevent the stall. My oil pressure also goes down to about 19 psi when I am stopped. When in neutral or in park my rpms are around 1000 and the oil pressure is about 30 psi. I can also feel an almost "bump" in the engine rythym when the rpms get down to about 700. I've gotten to where I put the car in neutral at stop signs and red lights as I'm in fear of stalling out at an instersection. Another thing that happens (and I'm not sure if this is relevant) is that my dash dims and brightens randomly when driving, but is most noticeable at night. I haven't done any work on it yet and was wondering if anyone could toss me some advice as I don't want to muck up something that would be best left to professionals. Thanks ahead of time!

 

Normal warm idle is around 700-800 RPM in N or P, about 600-700 RPM in D or R.

That oil pressure sounds a tad low; what is it on the highway? If hi mileage you might try a 10W-40 full synthetic motor oil.

If you plan on doing some work on the car I strongly suggest getting a copy of the HELM Shop Manual for that car.

The dimming display could be due to a grounding problme; not an easy fix with our digi-dash...

 

1200 RPM is normal for a cold engine. The RPM will drop as it warms up.

You probably need to do a minimum idle adjustment:

http://www.batee.com/corvette/dcrg/r...scuss_sim5.htm

 

Could be your torque converter clutch is dragging. If line pressure going to the converter is not high enough (a regulated orifice in the pump could be mucked up) or clearances within the converter are not correct, the clutches can drag.

 

65Z01: The pressure goes up to about 45 psi when I hit the highway, sometimes a little higher.
Cliff: I'll take a look at that, hopefully that's all it is
383vett: Is there anything I could do about that or should I take it to a garage?

 

I had a 5 disk converter freshened up and the clearances were not correct causing the clutches to drag. I was told about the oil flow restriction to the converter. The tranny has to be disassembled to find out if that's the problem. Make sure the motor an tuning are sound before you pull the tranny.

 

Just noticed that the ac makes the rpms go down too and the oil pressure has gotten even lower(13psi) when idling in drive.

 

I have changed and flushed the oil, changed the transmission fluid and the coolant, changed the battery and sparkplugs. So far there is a small improvement but the engine is still not firing right. Flucuations in the rpms continue and the threat of stall is still there. A friend told me that the distributor cap could be the culprit. Any thoughts?

 

First off , let me day this if you have a 85 vette you have an early model 700r trans m forget about fixing that one and update to a later [87 to 92] Trans they are a much updated unit and have an aux valve body which fixes the harsh engagement in gear and remember that corvettes use a special trans case so you need a corvette core i built my 700r in my 85 using an 89 unit and made mods to it and it works great drop me a note if interested in how i built it , as far as stalling goes , 1. clean the throttle plate assembly w/throttle body cleaner and a tooth brush real good remove the IAC motor clean the bore and the motor [carefully dont push the tip of the IAC back or your gonna ruin it !] when cleaning the throttle plate check to see how much wear is in the shaft if its excessive it will need replacement or rebushed [i can do this if you send it to me ] if it worn to bad your TPS voltage will radically change up or down causing stall or tip in stumble next you will need to look in a factory service manual and []engine warm] jumper your ALDL connecter and put it into [field service mode] key on engine off for 45 sec this will retract your ISC motor start the car up then you can adjust your MIN idle to spec [500 to 600 rpm depending on which prom you have] then turn the key off disconnect the battery and remove the jumper wait ten min reconnect battery fire it up [it may not want to run at first ] take the car out and drive it at 40 to 45 for at least 5 min your car should have completed the Idle relearn process , next check your TPS voltage and adjust if nec , this is all done assuming you hve gone over the engine to check for vacuum leaks first [spray around EGR and intake w/carb clean but watch out for leaking voltage from plug wire have a extinguisher handy, you have an 85 it is a one yr only on the ECM, MAF, injectors ect, so keep your eyes open for spares your gonna need em sooner or later , piece of cake good luck and have fun with your car!

 

For the OP, it could be your battery is really weak and dying or possibly your alternator. Mine did the same thing when I put it in reverse then I got a new batter and it was fine. You might try having the battery and/or alternator tested to see if either of them are causing the problem.

Hopefully this might fix your problem or at least eliminate something that could cause the problem.

Also for everyone else, what is a normal oil pressure on the digidash for an 89 supposed to be while in drive and idling? Mine stays around 19psi once warmed up and having drove for a while. But, while driving it is anywhere from 40 to 50psi or around that anyways possibly higher than 50psi. I know for sure I have a very small oil leak and by very small I mean I do not have to add any oil between oil changes, just enough to cause a bad smell once warmed up for about 5 minutes.

If anyone could help me with the normal oil pressure reading, then please do.

Thanks, Stephen