96' Grand Prix SE Spuddering

[Dustindell]

I've got a 1996 Grand Prix SE with 127,000 miles. I bough the car a year ago to drive to and from work, It has the 3100 SFI that knocks real loud at initial start up. Well a few months ago I was driving it home and noticed the acceleration seemed to feel bogged down. I limped it home and noticed the transmission smelled real hot so i figured it was toast. I bought a GM re-man transmission that was used and put it on, while i was doing that i tore down the motor and replaced most all of the gaskets excpet the head gasket. The first bolt i tried to take off stripped so i left it alone. I put everything back in the car, it fired right up. I put the wheels back on the car put it in drive and there are no issues what so ever with the car on jack stands. So i took the car off of the jack stands and back it down the drive. I start driving it down the road and the car spits and spudders, if you mash the gas it eventally takes off like it normally should and shifts fine. Once its up to speed you can hear the exhaust get really deep. If you try to accelerate when the exhaust has a deep tone it does the same spuddering then accelerates quickly. There are no misses or engine lights on the dash. I did replaced the fuel pump a couple months after i got the car because it went bad, i did the filter as well. I've used my volt meter on all the sensors in the engine bay and they all checked out as working (MAP sensor, IAC sensor, cleaned MAF, crank position sensor, ignition module). I replaced and checked all the vacuum lines. What should i look for next?

The main thing that has me puzzled is the fact that with no load on the tires the engine and trans run flawlessly but once you put a load on the tires its a completely different car.

Any ideas on what to check next would be appreciated.

[JamesIvey24]

i would unplug your maf and see how it acts. dont beat on it with maf unplugged, just drive it normal.

[Dustindell]

Alright just got back from driving the car around with the MAF sensor unhooked. Overall the car runs tons better, at initial acceleration there is a small amount of spudded but the car gets up to speed much quicker and with a lot less effort. So replace the MAF? I would assume the engine light is on because I have it unhooked as we'll.....?

[JamesIvey24]

If you wanna take a chance you could try "cleaning" the maf with the CRC maf cleaner any auto parts store sells, but my experience has been that its nothing more than "snake oil". MAF's can be cheaply had at any pick n pull salvage. Id also look to see if there is an "excessive" amount of oil in the intake area..mainly from the filter towards the intake if so..then this is generally a sign of a plugged up PCV system. That being said, the MAF could be dirty from oil residue, they are quite sensitive. So, if you find a buildup, make sure you clean your stuff out, intake tube from filter area, throttle body, etc.
and yes, the code is most likely from the maf being unplugged. on replacement, you can either cleat the code if you have access to a scanner, or unplug the battery for a cpl hours.

[Dustindell]

So I bought a new MAF and it worked for a day but I'm back to where I started. I went to the junkyard and grabbed an air temp sensor, throttle position sensor, and a IAC sensor. Put a new fuel filter on but still the same thing. So I dropped the fuel tank to check the sock on the pump, when doing so I noticed the vacuum line that returns from the engine bay to the vapor canister was rotted. I pulled the canister and found a large hole had formed in it and both vacuum lines connected to it we're rotted as we'll. so tomorrow I'm going back to the junkyard to grab a vapor canister and the parts store for new vacuum line. I will also pull the fuel pump to look at the sock and check connections.

Would a vacuum leak to the canister cause any issues with the way the engine runs?

[Dustindell]

We'll I just changed the vapor canister and all the vacuum lines. Found a slightly kinked fuel line right before the filter and fixed that quick. Took the car out and it's pretty much the same. If you hold the accelerator in the same spot the engine will spudder then take off with plenty of power then the power drops again.

could a clogged cat cause is?