Problem...

[Asleep Altima]

ok... thought the engine had an maf problem because the engine wouldnt idle and hesitated and stumbled on acceleration. last night we swapped out the maf and had no change whatsoever. went out to the car this morning and now it wont idle, it backfires thru the intake when you press the gas pedal and unless its floored - it wont accelerate either. even then, it stumbles and pops until it gets there. i pulled the codes from the ecu and got a 12, which is air meter circuit. that could be from when i unplugged the maf while it was running though. i reset it and ran it again all i get is the "all's well" 55 code. my thoughts right now are pointing to the throttle position sensor or an intake leak. was supposed to be at work by 6 this morning so now this is costing me money instead of just being a pain in the ***. i cant hear the fuel pump running either but it may be fully pressurized already too... fuel filter is only a week old too...ideas?

[Asleep Altima]

wealth of knowledge here...

[180fan]

Could still be a MAFS problem. Check the circuit for the MAFS, whether it's got continuity.

The popping and stumbling could very well be a TPS problem. Is this an automatic or manual?

The fuel pump, I don't hear when I start up my altima, but I do on my 240 with it's walbro. If you've an aftermarket pump, you might hear it whirr when you've got it in the "on" position from off. Don't take the key to "start". Then listen closely.

[Asleep Altima]

well... heres where im at as of last night. swapped in a known good maf and same problem. swapped in a brand new tps and still nothing. now it wont rev over 5k and it sounds like its suckin for air. barely idles and when you step on the gas, its like a carburetor with a bad accelerator pump... nothing happens... im thinking the engine is out of time on the cams. im gonna pull the vc and see what the chains and tensioner look like.thanks for responding.

[Ubernoober]

Why would the cam timing be out? What else did you do that you didn't put down in your original post. Without this information, the rest of us trying to help are going to guide you in the wrong direction most likely.

[Asleep Altima]

http://www.nissanclub.com/foru...98169

http://www.az240sx.org/forums/...18602

http://www.az240sx.org/forums/...18525

all links to whats been going on....

[Ubernoober]

Hmm. Lots of suggestions, but I guess nothing has gotten better.

We'll start with what I actually know and then I'll go on to guess later.

First, the black box that has a line running up to the air filter box isn't the EGR. It is actually designed to let air into the exaust to help complete combustion of any unburnt hydrocarbons running through the cat. It is controlled by a vacuum motor and a set of reed valves. This system can go dirty allowing exaust into the intake. This will certainly caus eproblems with fuel metering. Many people remove this, but the simplest fix is to pull the line off the vacuum motor and plug it. If the vacuum motor never opens, there cannot be any flow in either direction.

Second, it looks like you have tried really hard to focus on the MAF which is good since the symptoms support that, but it may be time to use that "known good" MAF and move on down the line.Any unmetered air getting into the intake will cause a lean condition. Check your gaskets and vacuum lines.Pull and plug the vacuum line off the EGR vacuum motor (at the back of the intake manifold). Aslo, make sure your EGR valve is working correctly. If it isn't closing that can be a major problem.

Se if that makes any difference and we'll go from there.

[Asleep Altima]

thanks for the replies. i have another engine/transmission combo coming in this weekend so im going to swap the whole package out. id like to continue to troubleshoot this but i need the car for work... the other engine is complete so the problem should follow the old engine. ill relay what i find when i pull the old engine.