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Rough idle sounds like missfire

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booster16g

Probationary Member
25
0
Feb 2, 2008
findlay, Ohio
I'd like to announce that I have added another 2g to my family, I'm now the proud father of 2 black 2g dsms, one 97 and one 99. Anyway. The 97 I just bought is a turd and I over paid for it, but I couldn't live without it. When it was dropped off it seemed to be running considerably worse then when I test drove it. It has a rough idle that shakes the entire car and it sounded like a misfire. The first thing I did was a boost leak test and found leaks everywhere, bov, t fittings, ic piping, and injector seals. The car was throwing an egr code when I got it and I took apart the all of that when I put my prothane motor mounts in, when I put everything back together the car read no code. It continued running poorly with no codes, then I replaced the injector seals and fixed all the boost leaks and it still ran like crap. Then finally after a few days it threw the misfire code I knew it should have been throwing a while before that... any ideas on the problem? The car does have a walbro 255 fuel pump and 550cc injectors, and a stock fpr. I just replaced plugs and wires and they are all firing.
 
As far as I know I have fixed all the vacuum leaks.... but it didn't fix the issue. Before I posted I had done a lot of reading on the issue and fpr is one answer I was seeing.. I'm not sure what the pressure should be set at for it tho. Also, I had heard that reading the fuel trim would help diagnose the issue.. unfortunately Im not familiar with how to read the fuel trim information. Thank you for the response, it kind of helped solidify my thoughts on the fpr.
 
Hey booster I was experiencing the same issue with my 99 gst. But my car is mainly stock. Now I removed the plugs and 3 were light grey and one was black and looked burnt. My uncle says it fouled the plug. Check your plugs wires and coil pack. My uncle had me changed the plugs, didn't change the way it ran. I changed the wires still didn't change the way it ran. So I changed the coil pack and boom fixed. But mine was doing it intermittently. Like
It would run fine. then all of a sudden lose all power and the tach would start going crazy.
 
The power transistor for the coil packs? Yeah, plugs and wires have been replaced and they all fire. But I have heard that even tho they seem like they are firing okay there may not be enough spark.... also, this problem really can only be felt at idle and low ram when in boost the car seems okay.
 
Booster with the car started and running and missing, pull the plug wires using a rubber handled pair of needle nose pliers. Start with the plug wire nearest the timing belt. Pull the wire away from the plug while the car is misfiring. If the motor shits off of runs worse then that wire and plug are good. Reinstall the plug wire and restart the car. Now pull the plug wire furthest from the timing belt. Again if motor runs worse or shuts off then that wire plug and 1st coil pack is good. Now reinstall the wire and restart. Pull the middle wires and see. What you are looking for is that when you pull a plug wire the motor in theory should shut off or run worse. If you pull a plug wire and there is no change at all to the motor motor then I would suspect it to be 1 of the 2 coils located on the drivers side between valve cover and the intake manifold on a 2g. The coil pack closest to the passenger side is for cylinders 1 and 4. Which cylinders 1 and 4 are your cylinder closest to the tranny and timing belt. Numbers 2 and 3 are on the coil closest to the drivers side. Cylinders 2 and 3 are the middle cylinders. Hope this helps. That was the issue I had with my gst just recently and how I was able to check
The coils.
 
I will definitely give it a shot! Thank you for the help, I would like to drive this thing before I store it for winter..
 
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