Service Engine Code 34, MAP Sensor?

[kustomkyle]

1986 Buick Regal Limited, 5.0L/307 CI Olds, all stock no modifications. It will gradually get to a point that it is a good running usable mode of transportation. But, over time, it will gradually start to run rough, to the point that it is undriveable. It's like a gradual roller coaster of running good to barely running, usually over a 3-5 month period.

Currently, the only trouble code is 34. I have no idea what this means other than what the Chilton's manual says, which is "Manifold absolute pressure (MAP) sensor output high (after ten seconds and below 800 RPM).

Can anyone elaborate as to what this may mean? I had a spare (new) MAP sensor, so I put it in with no change. The car currently idles ok (for this particular car), but as soon as it is put in drive the RPM drops and the engine starts missing. The engine skips and pops and struggles to get up to 25MPH, and when coming to a stop, it sounds like it is going to stall (but hasn't yet).

Previously, advancing the timing and turning the idle up helped. It still ran poorly, but I continued to drive it and it got better over time to the point that it was running ok. It reached a "peak", then I could gradually feel it missing harder/more pronounced over a week of driving. Now it's back to "don't drive me" mode.

 

[Clone TIE Pilot]

May be a vacuum leak somewhere, the CCC really hates any kind of vacuum leak. Don't overlook a leak at the intake gaskets either.

 

[kustomkyle]

May be a vacuum leak somewhere, the CCC really hates any kind of vacuum leak. Don't overlook a leak at the intake gaskets either.

I replaced all of the vacuum hoses a couple years ago one at a time. Not really a possibility on that one, other than if it is somehow the intake manifold. There would have to be an oil and/or antifreeze leak somewhere I would image, which it doesn't have (probably because it luckily has a cast iron manifold instead of an aluminum one). The only other thing it could be that I can think of would be the A.I.R. injection system, if that really affects anything other than the catalyst system.

I'm guessing this would have to be an electrical/sensor gremlin somewhere. Doesn't really make any sense how it runs fine then goes to garbage and back all by itself. Or it's just so screwed up the CCC system keeps recalibrating itself over and over after timing changes/etc.

Removed catalytic converter as I had a problem with the original clogging up and suffocating the engine (which is what the power level feels like again), but it's the same/worse. I do plan on getting this engine rebuilt so I can have a fresh start, but that has been the plan for almost 10 years now. Finding someone to rebuild a 307 Olds though has been a useless proposition.

 

[Clone TIE Pilot]

Intake gaskets can leak around the vacuum ports but still seal tight around the coolant ports. Engine vacuum can suck in the gaskets around the intake ports while not affecting the coolant ports. I just replaced my intake gaskets because a intake port was leaking vacuum, but there were no coolant or oil leaks just vacuum.

With a dwell meter hooked up to your m/c solenoid, spray brake or carb cleaner around your intake gaskets. If the dwell leans out, you got a leaking intake gasket.

Could also be worn throttle bushings causing a vacuum leak. The CCC will only work right on an engine that is working right.

 

[kustomkyle]

Intake gaskets can leak around the vacuum ports but still seal tight around the coolant ports. Engine vacuum can suck in the gaskets around the intake ports while not affecting the coolant ports. I just replaced my intake gaskets because a intake port was leaking vacuum, but there were no coolant or oil leaks just vacuum.

With a dwell meter hooked up to your m/c solenoid, spray brake or carb cleaner around your intake gaskets. If the dwell leans out, you got a leaking intake gasket.

Could also be worn throttle bushings causing a vacuum leak. The CCC will only work right on an engine that is working right.

Sounds like it's time to just have someone rebuild the old...Olds for the Oldsmobuick.