Thread: Engine Idles Fine, Kills when I Hit the Gas

Hey everyone, new to the forums. I own two grand prixs, an 04 which I drive and an 06 which my wife drives, Both with the L26.

I'm having a heck of a time with the 04, been trying to troubleshoot it for about two weeks. On the way back from the store (the parts store actually with a new water pump for my wife, unrelated repair), my RPM's took a nose dive and I almost stalled out. I pulled off to the side of the road and coasted for a bit, then accelerated and had the same thing happen. Eventually the problem went away and I made it home, accelaerating normally. The next day I started the car and it idled fine but as soon as I took it out of park and touched the gas even slightly it killed, completely this time. Started fine two more times, killing each time I put it in gear and hit the accelerator. Telltale sign of a dead fuel pump, or so I thought.

So far I've replaced the fuel pump and cleaned the throttle body. I thought fuel filter, but it revs normally while in park and the filter isn't all that old. Also, the car will creep forward or backward normally at idle but as soon as I even tickle the accelerator the RPMs drop to zero and it stalls out.

Totally at a loss, could it be the MAF? Should I just go ahead and replace the fuel filter? Or am I totally looking in the wrong place? Thanks everyone!

I would say it very well could be your maf. That's a pretty common sign for a problem with them when you touch the throttle just falls on its face. Try unplugging it while running and see if that make a difference. if you can accelerate I'd say you found your problem

Unplugged the MAF and started it up, engine just kills, no idling, after about 3 seconds. Tried a couple times with identical results. Not getting a code either. To be honest I thought the car could run without the MAF so is it strange that it's just killing with it unplugged? Also, would the MAF allow the engine to rev normally in park, but not drive or reverse? Confusing problem, thanks for the tip though!

Can you keep it running and try to rev it?

It should run with it unplugged.. So it will rev fine in park but not in drive? Does it bog real bad in park while revving? May have a plugged converter

MAF my 2000 GRAND PRIX GTX did the exact sane thing I first cleaned it and then that didn't work just replaced it and fixed ever since but there are other things that can cause the maf to read bad.

Seems to rev ok while in park, like it's supposed to, what's the easiest way to check for a plugged cad? Exhaust flow seems normal.

Remove upstream o2 and use an exhaust pressure gauge but not ever one has one of those. Does it lack horsepower?

Use a back pressure tester to confirm test for a clogged catalytic converter. Remove an upstream oxygen sensor install a back pressure tester. Usually the specifications will require back pressure to be below 1.0 psi. at idle and no more than 4 or 5 psi.at snap throttle.

A hair under 200k miles.

Thanks, definitely going to check on both the cat and MAF tomorrow then. I've never seen it though where the car will rev fine in park, but not accelerate in drive or reverse. Would I still get exhaust flow (it's easy to see being in MN) with a clogged cat? Anyways, I'll let everyone know how it goes in the morning, thanks for all the advice!

No check engine light... actually the check engine light I had for the evap sensor turned off once I installed the new fuel pump, so I got that going for me :P,

The MAF on my wife's car is the same so I can just do an easy swap, so i'll check both again tomorrow. One thing I will say is that it seems to start with extra "vigor" i guess you could say now, like it's getting more gas at start up (foot off the pedal), though that could just be the new fuel pump and clean throttle body.

Just thought of something else, when I pulled off the throttle body today, a small amount of gas leaked out of the intake manifold. I also noticed some in the snow when I first had the problem and ended up just pushing the car into the garage. I honestly don't know if that's normal or not. I would presume so, but it seemed like more than should be there.

Could very well have been, I had gas on my hands, but it was also a yellow/green in color, i'm going to say it was probably coolant.

Update:

Went to town with a hammer on the Cat this morning, nothing. Tried unplugging the maf again, same problem, only this time it wouldn't even idle, it fired and killed right away like yesterday. I turned everything completely off, removed the key, tried again, same issue. Now however it kills while in idle if I touch the gas, MAF or Not, and when I can get it to idle, it definitely sounds like it's idleing a bit high. Got it to move enough to back it out of the garage a bit to put a jack under it. Still need to try to swap for my wife's MAF tonight when she gets home to see if that makes a difference, and thinking I should just bite the bullet and throw a new fuel filter on too.

Update 2: Pulled the MAF off completely and started checking for resistance on the pins with a multimeter, systematically moving across until I got a reading. I'm registering about 20~24 ohms on one of the pin combinations, the rest read nothing at all (5 pins, so 5x5 =25 combinations). This seems awfully high since most new parts im finding online should be in the 10ohm range. I may have found my culprit. Also, closed my front garage door and opened my back one to keep it as dark as possible, the cat isn't glowing at all after several minutes of idling. Not sure if that's enough, but the exhaust flow out the back feels strong too, I can feel the beat of each individual cylinder opening. itching for my wife to get home so I can compare hers.