Surging Rpms, Hanging Idle, Losing My Mind

Discussion in '1994 - 1995 Specific Tech' started by Blau, Nov 27, 2013.

  1. Hey guys! I was wondering if anyone here might have some insight into this plague of an idle I have. For the past month or two, my 2000 5.0L swap, virtually a '94 GT in a New Edge chassis, has had a terrible surging issue.
    Short background: She idles anywhere from 1000-1500 rpm (usually 1050-ish).. between shifts my rpms jump drastically/surges to ~2500, sometimes 3000+.. surges up and down from 2000 to 1000 rpm while rolling at higher speeds in neutral.. and hangs around 2000-3000 rpm until I come to a complete stop, at which point, every single time, the idle returns to somewhere around 1100 (occasionally much higher). This doesn't happen all the time, but most of the time, and it gets progressively worse/greater jump the harder I drive my car/the more it's warmed up. Just driving around town, it's as if I'm a rookie keeping my foot on the throttle while I shift -- but I'm not! I replaced the IAC a little while back, which resolved an issue where idle would rarely ever drop below 2500 rpm. My IAC is brand new -- can't be that. My EGR is bypassed, and there are no vacuum leaks there. I've thoroughly cleaned my MAF and 70mm BBK throttle body, checked everything I could in the intake... My butterfly looks fine, and sits 1 or 2 mm ajar at rest, which I understand to be normal so that a seal isn't created. My TPS is reading .92 volts, so that's working fine. I'm getting 32 pounds of fuel pressure at idle warmed up. Somehow I must be taking in extra gas or air when I shouldn't... But I can't figure out how! All of my mods (related and unrelated): 4.10's, Pro 5.0 shifter, b cam, 1.6 roller rockers, 289 hipo heads (I know :(), 70mm BBK throttle body, BBK longtubes, BBK o/r x-pipe, Mac catback, Tociko shocks/struts, H&R springs, A/C delete, underdrive pullies, Aeromotive fuel pressure regulator, Typhoon upper and lower intake, and stock injectors.
    My air filter is pretty old and beat up... but I don't think that could cause so much of an issue at all. I pulled self test codes, came up with quite a few codes. Some of them I'm guessing are from the swap. Unfortunately, I don't have my O2 sensors hooked up. I have extension chords coming in the mail for them. The car is in open loop and running rich at all times, gotta get them working so I can stop getting 10 mpg!
    327 - DPFE or EVP circuit below minimum voltage of 0.2 volts
    565 - Canister purge circuit failure
    176 - o2 Sensor circuit indicates system lean (left side)
    556 - Fuel Pump circuit failure
    172 - o2 Sensor sensor circuit indicates system lean (right side)
    146 - I can't find any info on this code anywhere
    411 - Cannot control rpm during KOER low RPM check
    147 - driver's side (post converter?) o2 sensor
    Any ideas fellas? I'm brick-walling and at wits end!:bang:
  2. You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. :D

    It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 134,000 hits, which indicates it does help fix idle problems quickly and inexpensively.
  3. amen. idle will be fixed, case closed