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Discussion Starter · #1 ·
I hope this is in the right forum

Hello all you tech gurus! I am having a hell of a time with this car. It just came into my possession and it is a nightmare.
I believe it has 120k miles on it. (dash odometer isn't working) I received it and it was driving ok except for the fact that in 3rd and 4th when accelerating slowly the rpms would bounce between 1600-2000 and I had to step on it to get it up to speed. Kind of a pain.

Anyway, I went to work on it, and it was pretty grimey under the hood. Gave it a good bath and drove without much changing. The next day I tried changing the TPS as I was told by many people this was probably the problem. No change. Was driving it to get my kids when suddenly when I took my foot off the gas pedal it stalled.
Side of the road, turn the key, start then immediately stall. Scan tool showed long fuel trim at -40%
No check engine lights, no codes, nothing. I changed the plugs and wires and I'm glad I did. Someone put platinums in it and they were gapping at over .100
New iridums and wire set and it started right up. Now when I go to put my foot on the gas, sometimes it works, sometimes it stumbles and almost stalls.
I changed the fuel filter today. Had to cut the line and patch it since it was rusted in place. Still the exact same problem persists.
fuel pressure koeo is about 46-48 psi. I pulled the vac line to the regulator and it shot up to 50psi and stays there running or not. No change in drivability tho.
If I disconnect the MAF, it will stall and not run and not re-start. I thought it could run without the maf, but I guess not?

Anyway, I am running out of ideas and not really wanting to just throw money at this thing.

Please help!

Thanks
 

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Could be a variety of things on older cars with spotty maintenance history...
  • clogged cat
  • vac leak (line, connector, etc.)
  • warped/cracked upper intake manifold (vac leak, as well)
  • leaking lower intake gasket (probably worth a change, even if not causing current issue)
  • bad O2 or MAP sensor
  • wiring issue hidden somewhere

There's ways to diagnose/inspect most of these for free or close to it, and the DTC may not light until it's a much worse failure for some.

If it's not running at least rough without the MAF (VE mode based on MAP), it seems like a vacuum leak not letting the tune adjust properly. The EGR tends to warp the plastic UIM over time, and can be permanently corrected multiple ways, if you get to that point.
 

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Discussion Starter · #3 ·
Thanks for the responce.
I've been diagnosing it. Def not a vac leak or a clogged cat.
Map sensors are moving on the scan tool and map is showing pressure and moving. Doesnt mean they are good, but getting a reading at least.
I'm leaning towards bad wiring or ground.
I'm trying to trace the 5v reference wire and grounds.
I'll keep trying
 

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Buick Lucerne CXL 2007
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Thanks for the responce.
I've been diagnosing it. Def not a vac leak or a clogged cat.
Map sensors are moving on the scan tool and map is showing pressure and moving. Doesnt mean they are good, but getting a reading at least.
I'm leaning towards bad wiring or ground.
I'm trying to trace the 5v reference wire and grounds.
I'll keep trying
I would check out that MAF wiring. Try some CRC, clean it and the throttle good. Trans filter, also would check the oxygen sensors. Just upgrade all of the small necessities. MSD 8224 coils are pretty decent, for correct engine timing.
 

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Discussion Starter · #5 ·
The strangeness continues.
Fires right up. Idles perfect.
Disconnect the maf. No change
Disconnect the map. No change.
Disconnect tps. No change.
Scan tool shows the computer is still getting readings from the sensors!
No check engine codes.
Plugged it all back in. No difference

Funny thing is, map shows 10 psi at idle! Whether the sensor is connected or not.

So im leaning towards bad wiring or bad ecm?
 

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Ya, that's a problem. I'd try running a multimeter between the PCM connections and the sensor plug. There's a few places online you can find the pin diagram, usually engine swap sites like the Fiero guys.

A fresh MAP sensor from a yard car may be the ticket to some help for cheap (same style the car requires... 1bar on N/A, 2bar on S/C).
 
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