Engine Close to solving rough cold & hot idle, I think, but not sure how to move ahead

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Dec 17, 2021
Still working through my rough idle on both cold (really rough) and warm (a little rough with random stalls). I did set my base idle and a vacuum leak along the way while working through the checklists on the site but now I am kinda stuck. Now, when cold, the car starts and dies once. On second try it starts, idles at 1200 RPM for about 30 sec, then slows down to about 750 RPM and then idles very poorly and I struggle to keep it running. After about 2 mins of rough idle, it smooths out at about 750 RPMs but randomly sputters, then smooths out again. Eventually it will just sputter and stall. If I pull the SPOUT it idles smoothly and does not sputter or stall. I replaced a few sensors (IAB, ECT, TPS and reset base idle with SPOUT removed) because of the error codes I was getting previously but now I really think my problem is electrical. Here's why. From the beginning of my issue, I have been getting the KOEO codes 15 and 96. I replaced both fuel pump relays and have good voltage at the pump, relays, ECU. I gave up on code 96 for a while. I dumped the computer memory and took the battery out of my code reader to dump that memory as well. Now, the KOER I get codes 82 (key on engine off code), 22 (BAP sensor out of range), 61 (key on engine off code). Car was warmed up when test was run. Disconnected the battery for 30 mins and ran the KOER test again and this time got 82, 12, 22. I also noticed during my last year of troubleshooting with the checklists and code reader I have never received code 11 and per the checklist if I never get 11 that means I have some sort of electrical issue. The only thing I have done with the car on the electrical side is upgraded the alternator to 3G and I did install another ground wire, as recommended by the checklist. In the past I have also received engine running codes that make no sense, like 62 and 2. Lastly, when the KOER test starts in the very beginning I expected to see "8" to show it was an 8 cylinder, but it always shows "0".

So, I apologize for the long post but I now am looking for some suggestions on how to move forward to see what electrical issues I could be having. Car has been sitting in the garage since April of 2021 and its killing me slowly. Car ran great for about 5K miles before this stuff started happening.


93 LX Conv, original motor (32K miles), original AOD replaced with TREMEC TKO600, boat load of suspension, brake and drive train upgrades.
First thing I would do is make sure all your grounds are clean and good from the battery to the block and block to the frame etc..When you get out of range codes it usually means the EEC is reading improper voltage. Take your salt n pepper shakers apart and clean the terminals although they may need all of the wires repinned on both halves and have the harness removed and bench tested........

Also when I do a base idle reset I do this...

Pull IAC and Spout connector and start car....If it wants to stall raise the throttle stop screw until it stays running or use your foot to keep it running until it warms up and runs on its own..

My camshaft recommends a 1200rpm idle but I set my base idle to 850 but when spout is connected my idle maintains a 1200rpm idle still then I shut the engine down and reconnect IAC and Spout connector then I do a ECU reset by disconnecting battery and touching the positive and negative terminals together then I pull the headlight switch and turn the ignition key like Im starting it to quickly and completely drain down the EEC to .000 volts DC.

I then Restart the vehicle and let the idle relearn for about 2 mins...If idle doesnt balance out after 2 mins shut the engine down again the pull the IAC and Spout connector again and set the idle 100rpm's higher then do an EEC bleedown and retry again..

If the idle balances out after 2 mins I then turn all the accessories on plus 1500 watt stereo system and put a huge load on the alternator for 2 mins...After 2 mins shut the accessories off and shut the engine down..

Let car sit 2 mins and then restart car....It should idle good and like normal...

If not Check your IAC for vacuum leaks..I found vacuum leaks on 2 different IAC's that I replaced then stopped the leaks and put them on my engine and both worked beautifully..

I see in your signature you switched from an automatic to a TKO600...Everyone says that you can run a stickshift off of an automatic computer and is true but not without running issues and the transmission setting is the issue..............

Heres the spot in your bin file that needs to be addessed.......A chip is one of the ways I know unless you know someone that can burn aa updated bin file into your ECU...

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Even though my vehicle was factory 5 speed and I have an A9L computer I have my clutch pedal switch bypassed and the engine couldnt see when the clutch was engaged/disengaged so the idle reved high around 1800-2000rpm's and came down slow at every stop until I pulled my VSS then the idle hung around 1500....

Seeings I run a chip I changed my setting to NO Trans Control and No clutch switch or gear switch in a forced neutral state and now my idle acts like it should....

The VSS has some influence on the ECU and how it performs too as this is everything thats speed activated or controlled....

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Another thing that comes to mind is the 22kohm resistor on #4 IDM circuit..........You may have to replace it...............Its 5.9" from the EEC connector..

When they go bad they stick in the open position and let pure voltage through.............

A resistor is a very fundamental component that we use in almost every circuit. It has two terminals, and it acts as a passive element in both electrical and electronics circuits.

If this guy fails to operate we get serious issues in our circuits. In worst cases can permanently damage our circuits.

A resistor fails to operate mostly because of over current and voltages. Humidity and moisture are its enemy too and being at the firewall isnt an ideal placement....

Good Luck
Last edited:


Oct 20, 2022
For what its worth, I read that you are running a manual in an auto car. If the computer was swapped to an A9L and not the A9P, note, the lack of ID sticker. Might want to confirm the correct HEGO harness is installed. I know the pin out is different between A9p vs A9L for the O2 sensor harness and there is also a jumper in the harness that is different respectfully. I have heard the wrong harness will cause short at minimum erroneous senor voltage and at worst a burnt trace or fried component on the pcb. You might be able to identify your ecu by disconnecting HEGO harness and checking pin voltage for each version and see if that tells you something. I don't remembers the fine details but I came across this when chasing o2 problems related to long tube header install. Somebody here can expand on that. Also try unplugging the O2 main harness at the inner finder connector and running the car in open loop/cold and see if some of your electrical codes clear up. Dump codes and recheck with o2 harness unhooked. In open loop it won't throw a code for them as it isn't even looking for them. Just shut it down b4 closed loop. Easy quick and cheap. Just trying to help think outside of the box you are in. Also, watch the YouTube video by Matt "EEC Jesus" with Leech Motorsports. He explains the factory eec iv code and why we run into issues when adding parts to untuned eec. I am in the process of acquiring Quaterhorse and tune some of these shortcomings out of my life. Let us know what you find.

Good luck my friend

P.S. jut thought about this, are you running an MSD? Might want to swap back to factory plug at the coil and see if it is part of your problem. Also, sounds like you might be getting out of the idle timing and into part throttle timing map. If you have a glitchy tps, it will cause this too.


Oct 20, 2022
Also, possible bad pip in distributor causing one or more cylinder misfires and or weak spark due to improper coil saturation. You can see this with an oscilloscope if you have access to one. The fact that it clears up when you pull spout. That defaults to base timing and preprogrammed ignition trigger. With spout in, the eec uses pip signal to adjust dwell time. If pip is bad or faulty the eec will clip the dwell time unnecessarily causing weak or no spark even with good module, plugs, wires, cap/rotor and coil but, being in part throttle timing table will clear up some when spout is pulled also. If high idle or high idle timing clear up every time you key on key off. It might be the ratch detecting a tps voltage drop after start and seeing the voltage drop as the new idle base voltage and assume that any change in voltage (idle screw adjustment KOER or short in tps wire/sensor) as a part throttle condition and change timing and fueling trends. This resets every key cycle and you can monitor tps voltage to see if there is any drop without outside influence.