Greetings everyone. I'm the proud longtime owner of a 2004 GTP who's been my baby since 2008. Unfortunately, ever since I could remember, I've had a surging/sputtering/bucking problem with her that's been worsening over the years.
I first noticed it as a proper concern back in 2012, where a fairly steep hill was on my path to work. Going up the hill at normal speeds, the accelerator would feel slightly unresponsive as I would have to push it fairly far down before it would downshift and work its way up. Before it would shift (although not in-between or hunting for a gear imho) it would buck a bit and surge before letting off and reengaging the accelerator and everything would be peachy. "It's getting up there in the years," I thought. "Probably needs a new fuel filter or something but oh well no worries for now!" Other than that, I continued to race around like your average GTP owner on flat surfaces until the past year or so.
Now more recently it happens everywhere regardless of conditions, ONLY in a hard acceleration and especially on WOT. It doesn't matter if its pinned from a stop, driving down the street, or cruising on the highway - you can hear the whine sputter in and out and many times the speed moves up at a crawl if i'm lucky. Here's a quick example on video. You can usually just power out of it especially if you ease into the pedal in the low end. But at higher speeds, even with a light foot, it's pretty likely to happen. But that's the thing: some days it acts much better or like a completely brand new car. For example, here's another video of a hard acceleration (increasing to WOT) where it sounds and acts like it should. That was taken around the same time as the previous one. Average day to day driving is pitch perfect EXCEPT if I have to get onto a highway, pass someone, or bolt my way into heavy traffic.
Okay so here's the hard details: This issue started and has gotten worse before I started swapping out parts but for good measure: I have a open cone filter, flipped top motor mounts, and a 180 thermostat. Those have mainly been thrown on to combat some heating issue paranoia the car has had over the years (works great btw).
I've taken it into a trusted shop and together we've checked out/replaced to no avail:
- Spark plugs+wires (once in 2013 by a different shop, and 2015)
- Coil packs are reading normal
- EGR Valve seems good
- Fixed a couple small vac leaks + all s/c vac lines
- Fuel trims are "surprisingly right on the money" considering its age
- Replaced fuel filter
- Replaced BBV
- Replaced PCV valve
- Fuel pressure ok and injectors are good
- Cleaned throttle body
- MAF reading normal
- O2 sensors working and cat is flowing good
After some of the vacuum work, the problem has subsided randomly throughout the day. Yesterday I took it for a spirited drive down the highway. Going on the onramp it accelerated like I've never seen before. I would be cruising and just randomly WOT for the fun of it. I turned around and went to pick my friend up to show it to him (hadn't been turned off at all) and getting back on the highway it was crapping out again.
Now my tech looks at me like I'm crazy when I show up for a test drive and it acts normal even though it was sputtering on the drive over! He says everything checks out and doesn't want me to throw money at the wall anymore. He did say the ICM could be wonky - not broken but just screwy where it may get too hot and start messing up under load. But I'm tired of replacing stuff on a crapshoot. I've scoured forums such as these for years trying to figure it out, I would really appreciate some assistance in restoring my baby back to where she belongs! I hope the videos will help simulate what I'm talking about as well.
Originally Posted by SneakySnaykes
