Sputtering.. some kind of misfire??
 

For a few days now this has been happening, I thought it was bad gas, but I have added gas twice since and it still does it.

Well what it does is (pretty much from a stop or when I'm coming to a stop but speeding up again) my car will like sputter and go slow. I can hear it because of my exhaust, it sounds like.. bup,bup,bup,bup.. like backfire sounds but a little lower and quicker sounding. If I let off the gas it will stop and I will accelerate like normal. From a stop if I go slow and take it easy. my car will go fine, but if I just give it a little more gas (not to the floor, but just a little quick) it will do it. If I floor i, it will do it and barely go anywhere, just moves a little with the sputtering.

At first it was just like a little pop, almost like a backfire when shifting, but just normal acceleration, and now it will do it pretty bad if it downshifts into like second of first or when coming from a stop.

Anyone know what this can be. I have the day off tomorrow and I am going to inspect my engine.

Engine mods I have:
Header (maybe a bolt is loose, came loost, leak?)
Intake (don't think it is really from that)
Exhaust (probbaly not)

Also, I had the RRM piggyback, but took it out and hadto reconnect one of the wires... the red/white one.. maybe that came loose? I will chec that also tomorrow.

Or it could be something in the car. I changed the spark plugs about 2 months ago, but they haven't given any problem.

I'm thinking I might change the fuel filter?

yea i having the same exact problem but i only have intake

How many miles do you have?

As a long time 4G63 owner I might be able to help with this one...Did you have your defroster on when this happened? It seems to me that there is something with the A/C/defroster that causes alot of stress of the electrical sytems and will cause the car to sputter at very low RPMs i.e stopping or standing. I haven't tried the grounding wires yet but I would guess that they might help.

I can't remember if I did, but I usually don't drive my car with any A/C on, but I will check when I go and drive today.

Alright, I just went out and looked. I popped the hood and when I push down the throttle cable the engine starts jerking a bit. Not if I push down a little, but maybe towards half throttle. This is just revving it up not even driving.

I just took it for a drvie real quick, A/C and defrost was off and still did it.

From a complete stop, I did just a little over half throttle to see. It started sputtering and I was barely moving. I just kept on the gas and it finally like caught up or something and started going like normal. But I didn't even release the gas but it caught up.

Could it be the header(RRM)? A lot of pressure on the low RPMs. MAybe the gasket is broken? Maybe I thightened the bolts to tight. But I have had the header for like 6 or 7 months now. Could it just start doing it now?

If it is the gasket, where should I go for a new one?

did your mas aitrflow sensor come unplugeed?
the car has a emergency run mode that the ecu tAKES OVER WIHT WHEN CERTAIN SENSORS ARENT PLUIGGED IN I HAD THIS PROBLEM ONCE BEFORE i though it was snapped on all the way but it wasnt securly conected and that what i got it drove me nuts for days then i brought it to the dealer and they tried telling me a sensor was busted and to buy a new one

check harnesses lots and lots of harnesses

Will do.

Didn't work. I just went around pushing on all harnesses including the air sensor one and it still does it....

Anyone else have ideas?

Mine was doing this for a while, then one day (monday actually) it threw a CEL, so I popped on the code reader. Misfire on 4. I looked at everything, it all looked secure, all the plugs were in perfect shape, so when I tossed it back together, swapped #1 and #4 plugs... seemed to take care of it... but that's just some mumbo-jumbo...

As for a real solution... I don't got one. But I did have the problem.

To me it really sounds like bad readings from the MAS. If you reset the car (disconnect battery for a bit then reconnect) it whould fix that. Our ECU's are wacky like that. I also get that little stall/jumpy thing if i have my defroster on, AC is fine though.

Also if your runny the piggy try soldering the wires if you havn't... many do this and fine the car runs better as the connections are better.

does it sound like its coming from the valves? my car has the noisiest valves ever