This site has been a big help in figuring stuff out on my 19994 Deville (4.9). Love this car! Had a 70 Fleetwood as a teenager, a course I did not know what I had at the time. The problem I’m having is it is running rough. It will shake as I give it the gas, almost like it is misfiring. If I start from a dead stop going up a hill the engine really fells weak. I did a complete tune up 1 year ago, plugs, wires, rotor, cap, fuel filter, pvc. (i'm assumeing plugs,wire and cap still good:hmm: ) Bought them from the dealer in Norwood, Ma. I also had the coolant drained and changed, no tstat. I cleaned the throttle body and egr tubes, no change. The first thing I started with was checking to make sure a wire did not come lose or rubbing against something, they seem ok. I used the on board to check the t-stat operation, it is opening at around 108 and closing around 92 and seems to run around 97. I have seen all the post on ISC motors and TBS sensor. The gas mileage is around 12.5 it has slowly dropped from around the mid 14 m.p.g.. Just looking for stuff to test. Do not want to just start changing parts.

THANKS!!!!

turn your key to a notch ebfore ignition and depress the "off" and "warmer" buttons in your car. Hold them down and the information center will go hawywire for a second and it will show you if there are any diagnostic codes that indicate a problem.You could have a bad EGR valave, which may restrict the airflow in your powertrain. If thats the case the code is going to be p036 for your OBD I '94. If not than you may have carbon buildup in the engine, try taking it on the highway and doign soem wide open throttle a few times .

The gas mileage is around 12.5 it has slowly dropped from around the mid 14 m.p.g.. Just looking for stuff to test. Do not want to just start changing parts.

THANKS!!!!
Have you checked the FPR as well as fuel pressure?

Sorry, I Forgot To Put In The Codes I Have.
Po30 I.s.c. , Rpm Out Of Rangr (history)
P031, Shorted Map Sensor Singal (block Lean) (history)
Po52, Pcm Keepalive Memory Reset (history) I Releaned After
Cleaning The Throttle Body
1039, Everyone Knows This One!!!

I Did Check The Fuel Pressure, It Was 35-40.
I Also Through In Some Cleaner In The Tank And Took It For A Nice Highway Ride From Dedham Ma. To Providence Ri. On A Sunday Morning.

I'm Going To Try And Check All The Vacum Lines Today. It Is Cold Around Here.

Thanks Again For The Input!!!!!!! I Have Learned A Lot On This Site.

[QUOTE=darcy]
P031, Shorted Map Sensor Singal (block Lean) (history)
QUOTE]

That MAP sensor code will make the engine run like you describe.