Just tried to start the car today after it had been sitting for a few hours. It'll start flawlessly, but right after it starts up after cranking, the RPMs drop straight down and it stalls. It won't hold its own at all, unless I warm it up fully and slowly let the throttle off, which is followed by a crappy 500 RPM idle. The first two or three times I did this I was getting a constant MAF code 34, but it stopped after that, and now I have no codes, but the problem is still there.
I did quite a few searches on this, most not coming up with anything useful as I couldn't search for "code 34" since you can't have any words with less than three characters in it.
Anyway, I've tried disconnecting the MAF sensor, and the tap test, neither of which change anything at all. The inside of the MAF looks fine as well. I've also reset the memory, and that didn't do anything either. There are no vacuum leaks that I can see.
The car has had all the components of the EGR system aside from the EGR valve removed, if that makes any difference. I wouldn't think so, though, since it was all removed 20k miles ago and it has had no related problems since.
I'd appreciate any help. I'm sure its an electrical problem but I'm not sure what to look at first. This is really upsetting because I'm trying hard to love this car but its hard when I can't drive it without wondering if its going to die on me while I'm driving. I'm in the process of building a new engine for it right now. It'll probably never get to the car, though, since all of GMs half-hearted BS on this thing taking all of my money.

 

that definitely sounds like a maf problem....however, its rather strange that nothing changed when you unplugged the maf

i had the same problem, unplugged the maf, and the car was fine (about 2 months ago...still havent gotten around to getting a new maf relay or maybe even a new maf )

try getting a new maf power relay and maf burnoff relay, its fairly common for them to go bad

 

Phoenix,

Don't be so quick to condemn the MAF. The '34' you are getting is for a low MAF indicated flow at a given RPM and TPS position. The ECM uses RPM and TPS to calculate what is an acceptable range, and sets an error code if the MAF voltage is not within that range.

In your case, you have an '85 TPI, which is a bit different than the rest of the TPI MAF years. You have a Delco digital MAF, slower ECM, and separate MAF module strapped to the back of the ECM. Later years used a Bosch analog output MAF, a newer ECM, and no MAF module. But, back to your specific problem.

You need to verify that the ECM is getting the correct TPS voltage. Adjusting the TPS is easy enough. Adjusting it to the lower end of the tolerance range may help in your diagnosis. Try 0.50V or just below.

You also need to be sure the HEI is reporting the correct rate of reference pulses to the ECM. Check your distributor primary connections.

And even with a good MAF, you can generate that error code if there are leak in the intake ducts between the MAF and the throttle body. Those leaks can include the MAF seals, air dusts, the plastic resonator box, the rubber bellows at the throttle body, the TB mounting itself, the PCV system, or any vacuum leak on the engine. Don't overlook a failing power brake booster. It is also imperative that the PCV system is sealed, and that NO type of "breather" oil filler cap is used on a MAF engine.

You also need to make sure there is a clean air filter element installed, ad remember that your filter flows "inside-out", so all accumulated dirt and debris will appear on the inside of the cylindrical element.

Once you verify all those, you can continue to diagnose the electronics if necessary. We'll be here. Good luck.

 

I wasn't pointing straight to the MAF, I meant the whole circuit.
I know the 85 version isn't up to par in relation to the other FI applications of this generation. I'm planning on replacing the ECU away from the little 165-or-whatever baud one after the engine swap, repinning and all. For now I'm hoping the ECU holds out till then, though.
I checked the whole intake routing and everything's fine. It was converted to a custom one composed of PVC fittings, and all that along with the air filter are fairly new so I'm pretty sure its not that. I had one vacuum leak where I had removed the cruise control before (dont ask why), but that has been plugged. Didn't seem big enough to hurt anything anyway. That's about it though. The PCV system is all fine. Even has recently replaced PCV valves. The air system is tight.
I've reset the minimum idle to keep it from stalling, but this isn't really going to be satisfactory for more than as long as it takes to fix it. I'm going out of town for the night, so I'm going to check vacuum level and the TPS tomorrow. Can the TPS go bad, or does it just need to be re-adjusted all the time? And can you think of anything else that would cause this? I was going to go out and buy a new TPS, but at 30 bucks I can afford to try checking it first.

 

Vader touched on it, but I'll expand some. Take off the distributor cap and look at the module, wires from pickup coil, and terminals really close. Corrosion or split wires will lose the rpm pulse to the ECM and it will start, but die. Slow timing will sometimes cause this to a lesser extent, have you adjusted it lately? Be sure to disconnect the timing set connector before setting the timing. Things like this are hard to solve, throwing parts at it almost never gets it, at least for me.

 

And yeah, the timing was reset just a couple months ago after replacing a head gasket. I suppose it wouldn't hurt to look at it again though. I'll check the spark system when I get back, too. I have never replaced the plug wires before, but I could tell that the owner before me had done it previously. How often do those need to be replaced?
Anyway, I'll check the distributor and that whole thing tomorrow too. Any other ideas, or is that all it could be?

 

No, the TPS doesn't typically require adjustment for no reason. However, you indicated that you adjusted the minimum air position to keep the engine running. I'm presuming that means you increased the throttle opening, correct? That would necessarily cause an increase in the TPS output voltage, since the TPS is connected to the same shaft. What is the current TPS reading at the curb idle position?

 

I got it. The TPS was a bit too high so I readjusted it and it works fine now. Its been sitting for a few days though. Sometimes it just decides to work after time like that. So I guess I'll know if it wasn't the TPS if it comes back again.