MAP sensor

[vortec]

my dd has been running badly for a few weeks. slight miss at idle, nearly stalling just off idle, wimpy, and wants to stall anytime i give it more than about half throttle. no codes. i did all the normal fuel system stuff (filter, seafoam) with minimal change. O2, EGR, PCV, IAC ok. coil, dizzy, plugs and wires are all good. I'm down to ecm temp switch (about to replace temp gauge sender, too, but that's unrelated) or the MAP sensor. I know the MAP can go out of spec, but the computer doesn't throw codes as long as it's still getting some signal from it. so, i unhooked it to backprobe and the truck runs A LOT better, now. smooth idle, a little sluggish at low rpms, but knocks me back in the seat when i open it up. my air/fuel ratio gauge says it's just slightly on the rich side without the MAP which makes sense as far as the performance change.

before i blow $50 on the new MAP, I'd like to know if anyone can think of some hidden problem this would be masking.

vehicle is a '94 c1500 4.3L with 4L60e.

thanks.

EDIT: I finally got off work in time to make it to o'reilly, last night (i hate my job!!!). $50 bucks and about 2 minutes later, i had a major improvement. woohoo. I'll still give it a good basic tune-up before inspection (due this month) but it's nice to have it back in shape.

 

[Thunder]

I think you found your problem. When you disconnect the MAP the ECM goes into limp home and will run better. Disconnecting MAP is a common way to tell if the MAP is bad when other things have been ruled out.
Do you have a scanner? It will show if the MAP is operating correctly.

 

[vortec]

no scanner. maybe it's best to just replace the MAP anyway, since it has 131K+ miles on it.

 

[Thunder]

By your description it sounds like your MAP. The only other thing I can think of is EGR but it usually would still run bad when you disconnected the MAP, if the EGR was stuck open.

 

[vortec]

yeah, since you mention that, on the way home from work last night, the engine sputtered, nearly died, came back, then completely stalled. I popped the hood, reconnected the MAP and it fired right back up. If i manage to get off work before the auto parts stores close tonight (really heavy week/month for me), i'll pick up a new MAP. 45-50 bucks doesn't sound like so much after dumping $63 into my gas tank, last night. filling the K5 would cost about 90