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93 LT1 85k miles. I've been trying to chase this down since June (not a daily driver). So the car seems to run great, good power etc from cold start to closed loop/operating temperature. But I go full throttle once after getting up to temp and it starts acting nutty. At a stop, idle bounces from 500rpm to 1500rpm. Sometimes during this I get surging up to about 2000rpms. Power is quite noticeably low. Today when it was acting up, I pushed the clutch in and it just died like someone turned off the ignition but it started right back up, still acting up though.

There is no misfiring, when it's low on power it runs smooth, but is just missing a ton of power. It pulls real strong and idles dead steady until going full throttle which sets this off. Sometimes when the idle is bouncing it smells like it's running both rich and lean. The last data log I took when I was able to capture this had long term fuel trims around 108, sometimes even lower.

I've replaced the ICM, coil, TPS, IAC, fuel filter, injectors, and I'm lost. I don't think it's an optispark issue because I've never had any misfire issues, backfiring, problems pulling to redline or any of the other typical opti issues. At this point I'm leaning towards the fuel pump because I noticed the whining fluctuating with the funky idle, but I don't know if that's just caused by the vacuum controlled fuel pressure regulator since vacuum changes with rpm. But I don't think that would cause surging, or maybe it would.

I'm running out of ideas, does anyone have any ideas or dealt with anything similar?
 

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Could be a spark plug wire going out (if one of them is too close to the header/manifold excessive heat can take a toll). Have they been changed?
 

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You need to put car on an obd 1 scanner that does real time sensor data. Compare the sensor readings when running well, to readings when power is not up to par.

Since you probably don't have an obd 1 scanner that does real time sensor data; May I suggest the free obd 1 pc based scan program called "scan9495". It will read your 93 codes & do running sensor scans. Get it at, www.mediafire.com/?0elo4c935uc5s

To use scan9495, you will need a 12 pin obd 1 cable that connects car's aldl to usb port of pc based computer. Get at www.obd2allinone.com/aldl.asp

Also, on page that has scan9495, you will need Microsoft dot net framework version v4 or newer. You can also get it from Microsoft site.
 
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