Stumble at low load
Stumble at low load Alright so I just bought this cherry WS6, it's bone stock, 2000 A4, and has 25k miles. I did a 10 hour drive home last night in it and after about an hour or so it developed this stumble/miss. It ONLY happened above 65mph-ish and only at very light load. If I was on flat ground and had cruise control on, it'd start bucking. At 80mph, it was enough of a load to drive smooth. Sometimes it'd disappear for a while and then come back.
I did some poking around and cleaned the MAF and checked the ENG SEN fuse. Fuse looked fine. O2 sensor wires I traced and there is no visible chafing and no pinch points. Checked the rest of the harness as well and bends looked good.
My only hint was that after getting gas once, I goosed it on to the highway and it threw a P0102 code. Cleared the code and it never came back. Part throttle and WOT run great, no drama. After I cleared the code, I did probably another 300 miles with no issue. Any thoughts on what I can chase down? Appreciate the help in advance!
I did some poking around and cleaned the MAF and checked the ENG SEN fuse. Fuse looked fine. O2 sensor wires I traced and there is no visible chafing and no pinch points. Checked the rest of the harness as well and bends looked good.
My only hint was that after getting gas once, I goosed it on to the highway and it threw a P0102 code. Cleared the code and it never came back. Part throttle and WOT run great, no drama. After I cleared the code, I did probably another 300 miles with no issue. Any thoughts on what I can chase down? Appreciate the help in advance!
Yeah I cleaned the MAF and it maybe helped, but I still was able to get the stumbling. I wasn't able to stay at the right speed long enough to see if it was any better or worse. Fuel filter is on its way, but I'm not convinced that is the issue since performance everywhere else is great.
I feel like it's got to be a misbehaving MAF or O2 sensor(s). I'd lean more towards the O2 sensors since the car runs great WOT but the MAF threw a code... I hate to throw money without a concrete diagnosis, but looking on RockAuto, a MAF really isn't too expensive.
TECH Apprentice
Joined: Sep 2016
Posts: 347
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But as G A mentioned, could just be your MAF.
So I replaced the MAF and it ran excellent for quite a while. Unfortunately, the P0102 code came back. I did a data log and it shows the MAF signal dropping to zero intermittently at low throttle, low load conditions. This doesn't set off the SES light though, only WOT will set it off. Still pulls strong and smooth though. I ohmed out the yellow wire between the PCM and MAF and it went perfect. +12V and GND also perfect...
Any thoughts on this? Still super intermittent.
Any thoughts on this? Still super intermittent.
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Yeah digging through the wiring diagram, I'm thinking I will find my fault between S110 and G110. I wish I had a way to scope the signal wire. If signal is being pulled to ground, then I would get an indicator to check for pinched signal... If signal was fine, then I could hunt for a bad ground... Oh well, I'm optimistic that I will pull the G110 and see some frayed connector or something or maybe a weak joint at S110.
I finally solved the issue, in case anyone else has something similar. On the passenger valve cover, one of the bolts that holds the coil packs on had its weird pointed top poking in to the wire harness. It ended up rubbing a wire and grounding it out intermittently. I fixed the wire and replaced the bolt with a normal hex head bolt. Problem hasn't come back!
