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Discussion Starter · #1 ·
98' disco with 120,000 chassis but 16,000 miles on new motor build. Sitting at idle after a 20 mile drive, world was at peace. Suddenly dies, starts right back up with a strange surging. Feather the idle it stays running. Dropped into drive and it acts as if the key is being turned off and on. To the beat of a drum steady, on off on off. Tack drops, power drops. Got it to 2k rpm and it took off like a rocket. second it drops down it starts all over again.
Into the garage and up with the hood. I have a rotted down running parts 98 in the yard as well as a cabinet of new parts on reserve. So here's the list as parts were changed.
Fuel was reading 31psi at idle. replaced with new delco pump. replaced filter as well because it was due. Dried tank and wiped out the bits of stuff. Now have 40 psi at idle... and the surge.
MAF removed, cleaned with crc MAF cleaner, still surging
replaced the MAF, still surging.
Idle air control
New Fuel pressure regulator
Throttle position
Downstream O2, bank 2
Air intake temp
Crank speed sensor
Plugs and wires.
Always dc the battery between changes.
Now have all this shiny stuff as an accessory to the surge. This is driving me insane and before I back this tea and crumpet British SOB into the yard and shoot it, Someone tell me what I'm missing.
FYI no codes showed other than O2 and multiple cylinder misfire.
I like to think of myself as the smartest raccoon I know, I hate to ask for help and I only get smarter by trial and error till something's fixed. I'm at a loss right now and it's too flippin cold to walk.
Thanks Rob
 

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Do you have a live data reader like ultra gauge? Look at TPS what is it key on not running? If it is way below say 11 check for 5 or 7 volts at TPS connector key on it is red wire not red/black that is ground

If there is only like .5 volt let me know
 

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To low, go pull up the rear carpet remove the round cover to expose fuel sender, there are 2 plugs, unplug farthest forward plugged into round disc go recheck TPS voltage, that disc is fuel pressure switch, it is hooked with TPS if bad engine no run, shorts TPS voltage

Let me know result, if voltage is much higher try to start

Put original IACV in replacing that requires ecm reset, just clean it
 

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Discussion Starter · #7 ·
Haven't had a chance to check it yet, apparently according to the wife I have kids. I'll get it in the morning but for the million dollar question. When I pulled the IACV, it came apart. Looked like the threads on the plunger were mostly nonexistent. So that said, resetting the ECM... Test book procedure or can it be done without a trip to the dealer?
Secondly, if it is a computer required procedure, is the $1100 diagnostic scanner AB sells capable of doing it?
 

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OK if it fell apart replace but you will need dealer or Indy shop to reset ecm, I suggest Indy shop if you can find one , you need the base reference reset some call adaptive values but you also need proper volt to TPS for it to work
 

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Discussion Starter · #9 ·
Ever stare at something till you're cross eyed? I have.
Just found the original IACV that came off during round 1. The replacement is the one that came apart. That's when I ordered the new one and installed it. New one is back in the box now, original is cleaned and bolted up.
On to TPS issue. Voltage at the pump side of the wiring is 5 volts. With it unplugged, voltage at the TPS is 5 as well.
Leaving the pump side unplugged but TPS plugged in. This time when starting, it stumbles for a minute between 500 and 800 rpm then settles in at 800 and idles smooth. Drop in gear and it holds with no stumble.
On the right track and you've made my Christmas list for this year...
 

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You need a fuel pump assembly, you may also need the ecm reset cause you messed with it so much like I did when I had same problem last month

Idle should be right around 700 drive it you may get lucky and it settles itself

To confirm plug the pump back in engine should die, I drove with it unplugged for a week or so no I'll affects while waiting for used pump assembly payed 135 shipped for used pump assembly you need the ael pump/sender

Ask on the other board you posted this to
 

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Discussion Starter · #11 ·
Tom, I left it unplugged at the pump and drive it 25 miles with no issues. Idle is holding good between 7-750 and all is smooth. Just ordered a new one since my 16 yo daughter drives this most days. Figure in for a penny, in for a pound. Have so much in this thing at this point, what's another 400... Ugh.
You my friend have been a life saver here. I owe you a steak. Rob.
 
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