I have had an intermittent stumbling problem over the past month with my car. Nothing provokes this problem, it will just come out of the blue and may act up for two seconds to several minutes. I can just be driving along and the car will suddenly start feeling like its running out of gas. Tonight when it happened it lasted several minutes and was mainly under acceleration and was like a muffled machine gun feeling/sound, repatitive popping. I would relate it to almost like bouncing off a rev limiter but this was going on throughout the lower rpm range (between 1k-3k rpm). The car has brand new plugs, ignition wires, and the cap and rotor are clean. If I had to guess off hand I would assume its the injector harness or reference sensors. Anyone have any ideas or advice?

 

One thing to try that's free is to unplug the AFM, clean the connector with a shot of WD-40 (it's dielectric) and reconnect. Worked for my S2 after replacing 100s of dollars in parts.

 

Have you checked your fuel pump? It may be on it's way out or there may be a wiring/relay isssue.

 

Well this happens so irregularly that I can never pin point whats wrong. It may go happen here and there over a day or two and then go two weeks with running perfectly normal, and it only happens while moving. I can feel it start happening and then come to a stop and it idles just fine, but once I start going again I get the stumbling of power. Last night was the worse episode from it yet, but if I would drive it past 3k rpms it would become smooth again, but below it was terrible.

 

+1 fuel pump or fuel filter or tank screen....just my .02

 

I replaced the fuel filter about a year ago. Where is the tank screen located?

 

tps?

 

Ditto

 

Any reasons for the TPS suggestions?

 

I have seen 3 different tps's crap out, where the low RPM range was almost completely shut off, or had a huge stumble. The one was so bad, that you couldn't get the car above 3k rpms. After unplugging it, you could drive and rev the car as normal.

 

Karl- When you saw these TPS problems were they intermittent problems or just a constant problem? From everything I have read I am leaning towards the TPS or AFM, I could switch out the AFM with another one off the other 951 but the problem happens so irregulary I wouldn't know if I cleared anything up or not.

 

UPDATE- The car starting acting up again today so I pulled over and unplugged my TPS to see how the car ran without it, and the stumbling was even worse with TPS unplugged. Lots of stumbling like I mentioned before but much more noticeable.

 

I've had a problem previously, similar to the way you describe yours, and it turned out to be a problem with a fuel injector. Have you had those flow tested lately?

 

You could try unplugging them one at a time when you have the problem.

 

You might check all of the engine harness around the injector harness (basically everything under the intake). I had a similar inconsistent "popping", or hesitation almost like a misfire. In my case it turned out the AOS hose was loose, slowly spraying oil under the intake and soaking the harness. With a 200k mile harness, needless to say most of the wires were brittle and had cracked sheathing. Anyways, my harness was shorting inconsistently and would cause a "popping" much like you described Potent915turbo86. Anyways, it's worth a shot. Usually it seems that most of these types of issues end up working out to be some sort of electrical or ignition system issue (check plugs, gap, coil/wire condition, etc).