92 Cadillac Deville 4.9 Intermediate surge issues
 

Purchased this car back in mid February with just a little over 80 thousand miles on it. Car ran great until about three weeks ago. It started running rough at idle, and I noticed sometimes when you get into the throttle to pass it would surge until you let off the gas a little. Diagnostics said E41, so I replaced the pickup module in the distributor and the car today ran amazingly smooth on my way to work, about a 70 mile commute. On my way home, the surge came back, but this time worse than normal. If I accelerated above 50 it would surge badly, so I started to limp it home. About a mile from the house I couldn't keep it above 10mph, then it stalled and quit running. I turned the key, restarted the car and for maybe a mile, it ran like there was no issues, then did it again. While it was running badly, I put the car in diagnostic mode while driving and it gave me an E70 error. But now that its sitting in the driveway, I have no errors. E70 is TPS, does this sound like something that would cause all the above?

An update. After the car sat for a while, I went out and pulled the line off the fuel filter and let the pump push fuel through the filter and into a gas jug, it pumps really good, so it may not be the fuel pump.

I took it another ride, and it ran great for about 7 or 8 miles, then started surging again when I got aggressive on the gas.

If it started surging badly when you got agressive on the gas, and it had previously thrown a TPS error, then it sounds to me that it needs replaced. Rev the throttle several times never going more than say 1/4 pedal. Verify it is running well. Then snap the throttle all the way as far as it goes several times. If the crappy run comes back and throws a TPS code, then I would definitly change it. Also make sure the vacuum line going to the MAP sensor (right behind the throttle body) isn't broken, and since you are checking all the fuel system parts, remove the vacuum line going to the fuel pressure regulator (to the right of the throttle body, it's a short line) and make sure no fuel drips out of it. I just replaced mine because the fuel rotted the line in half and I got the typical vacuum line leak surge. It isn't supposed to have fuel in there fyi! The reason I listed these areas is because on the 4.9L the only sensors that are must have's for the engine to run are the TPS, MAP, distributor pickup, and the ignition module also in the distributor. You have checked that the fuel pump is working, so check that fuel regulator and if it isn't leaking then it has to be an electronic issue.

Thanks Zynder.

I ended up putting a fuel pressure gauge on it and the pressure would drop to about 7psi when it studdered. I dropped the fuel tank and not only found it rusty, but the plastic baffles had broken up and were floating around. I replaced the tank with a new one, replaced the fuel pump and put another fuel filter on it, it runs like a champ again. A weak fuel pump was casing it to studder, was starving for fuel when mashing the pedal.