Intermittent, slight "stuttering" issue

[gacook]

I know this is a Porsche forum...but I respect the overall mechanical intellect of many of you here. With that said...

2003 Nissan 350Z. For the past several months, I've had an issue with it occasionally "stuttering" for lack of a better term. Slightly rough idle at the low range. And this is totally random. Sometimes happens at start up and goes away after a couple minutes; occasionally happens 2-3 hours into a long trip and lasts 10-20 minutes. Sometimes throws the CEL; sometimes doesn't. If it DOES throw the CEL, it always clears itself after it starts running "right" again. OBD reader says "random misfire"--no schit. So, here's what I've done to resolve the problem to date:

New plugs (old ones didn't look half bad)--no change.
New coil packs--no change
Ran seafoam through the system. Worked good for a week; then started the occasional sputtering again.
Cleaned the MAFS a couple days ago. Ran PERFECT for 2 days. I mean, it felt like a completely different car; brand new. Last night, it "hiccupped" for maybe 10 seconds, but that was the extent of it. Unfortunately, I still think the problem is there because I seem to be getting some slight power loss ever since the "hiccup." Very slight, still better than what had been happening, but I notice it.

I'm leaning toward thinking I need to replace the O2 sensors next (it IS a 125K mile car...). What do you guys think?

[Amail]

Had a similar experience with my 2003 Lexus. Cleaned MAF, ran much better for a few days then crappy again.

Turned out to be a split intake hose. Split was on the bottom so I couldn't see it. I suspect cleaning the MAF may have just pushed the split more closed temporarily.

With the car idling, spray carb cleaner around hoses and connections. If the idle changes as you spray, you've likely found the problem.

[gacook]

Originally Posted by Amail

Had a similar experience with my 2003 Lexus. Cleaned MAF, ran much better for a few days then crappy again.

Turned out to be a split intake hose. Split was on the bottom so I couldn't see it. I suspect cleaning the MAF may have just pushed the split more closed temporarily.

With the car idling, spray carb cleaner around hoses and connections. If the idle changes as you spray, you've likely found the problem.

I have a cold air intake. The "hose" is pretty damn big and in very good condition, but I'll give that a shot.

[stomachmonkey]

When was the last time you changed plug wires?

[gacook]

There are no plug wires; it has coil packs. Replaced them about a month or 2 ago.

[widebody911]

Originally Posted by gacook

There are no plug wires; it has coil packs. Replaced them about a month or 2 ago.

Do you have a way to check for fault codes?

[gacook]

Yup. The fault (don't remember the number off the top of my head, but I believe it was P3200 or something similar) is "Random Misfire." Doesn't specify a cylinder, or anything.

[ossiblue]

Years ago, I had an Isuzu Trooper that developed very similar symptoms. I replaced and serviced the same or comparable parts as you, but it didn't permanently fix the issue. Then, because every logical remedy had failed, I wiggled and then unplugged the harnesses from the main ECU, reconnected the harnesses, and the problem never reappeared. For me, the ECU was easily accessible and easy to disconnect/reconnect. Also, the technology in the car was fairly basic compared to today, but you could be dealing with something as simple as poor connectivity to the main ECU. It's worth a check, IMO.

[gacook]

Originally Posted by ossiblue

Years ago, I had an Isuzu Trooper that developed very similar symptoms. I replaced and serviced the same or comparable parts as you, but it didn't permanently fix the issue. Then, because every logical remedy had failed, I wiggled and then unplugged the harnesses from the main ECU, reconnected the harnesses, and the problem never reappeared. For me, the ECU was easily accessible and easy to disconnect/reconnect. Also, the technology in the car was fairly basic compared to today, but you could be dealing with something as simple as poor connectivity to the main ECU. It's worth a check, IMO.

I'll look into that; thanks. I cleaned the MAFS again, with similar results--car worked great for a few days. Started stuttering again. Based on this happening twice, I'm leaning toward thinking the MAFS is just on its last leg. Ordered a new one today (only $85). It'll get here in 2 days, and I'll test my theory.

I suppose with a 13 year old car, it wouldn't hurt to find all electrical connections I can get to and clean them up a bit.