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Discussion Starter · #1 ·
hey all. i have a 91 GT 5speed with moderate mods. the last mod i did was install Power Products 75mm TB and EGR Plate, and now the check engine light comes on. the engine also has a rough idle, but it's probably not related and it can still hover about 800-1000 rpm, cold and warmed. the oil pressure is really low all the time (about the lowest and second lowest bar in the dash). my air bag light always flashes, but i have an air bag installed.
i mention these cause they are just indicators of something else:
the throttle dies and becomes unresponsive WHILE i'm driving. with no throttle, the engine slows itself and stalls if i don't clutch. sometimes it stalls after i clutch, sometimes it just idles. kinda dangerous to lose power steering in the middle of a turn! i let the engine sit and warm up a bit 2 days ago. i noticed that every so often the rpms drop to about 500-600, the check engine and air bag light turns off, and my oil pressure guage goes to off. then it will come back to 'normal' and i'll be able to drive just fine. sometimes it does it every so many minutes. once it did it 3 times; once every 30 seconds or so. when it happens the throttle is comepletely unresponsive and sometimes stalls when i press it. i have a blaster 2 ignition, and i checked the wires, cap and rotor and they're still good. i replaced my cracked distributor module too.
my theory: it drives fine until it revs low and my oil and the 2 lights turn off. does the computer run a self check on certain parts? so when it runs a check on the bad part, it bogs down and shuts half the dash off? any other ideas?
 

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Any other gauges show erratic behaviour, such as the tach? or lights turning off?
For one it sounds like a serious vaccum leak, but also sounds like a bad battery ground or bad ignition switch.
 

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Discussion Starter · #3 ·
the speedometer sometimes jumps to 100mph, but oiling the wire should fix that. all my stock gauges display fine (except for the oil). none of the lights act funny. the only broken vaccuum line is gray or white from an unknown place located closest to the passenger's seat in the engine bay. dunno... it just sticks out and it's taped off and doesn't create any pressure. i have 2 guage neg and pos battery cables. i installed a push button starter, but it works fine. i'll investigate more into the vaccuum line and pull apart the dash for the ignition switch hopefully this weekend. thanks.
 

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Discussion Starter · #5 ·
uhhh.... i'm not sure what that is, so i probably didn't. TP as in Throttle Position? the black thing on the throttle body? i can check that connection later on as well.
 

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Make sure the negative battery cable goes to the lower passenger side of the timing cover, and that the motor is grounded to the body, and that the ground for the computer (runs forward along the driver side inner fender) is connected to the negative terminal.
 

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Discussion Starter · #7 ·
what a depressing weekend....
my ignition switch works fine and everytime i need it.
i could not determine where the vaccuum lines go to but they've been broke and this problem is new.
i thought i had found the computer ground, but it went to the fender and it had a dual wire crimped eylet. the other wire had an inline 1 pin and socket. dunno.
my neg cable goes to the engine block where the stock one was.
it ran good yesterday, but i tried it today and got stuck at a light *shame*. unplugging the idle air sensor gave an erratic idle, but the throttle would work (with the check engine light). we plugged it back in and then the problem would come back and i was helpless again. maybe it really is the idle air sensor... is there a way to trick the computer into thinking the sensor is there if i take it off?
we adjusted the tp sensor by rotating it, but with a rough idle and "The Phenomenon" we could not tell if it was better or worse. the old TB measures about 800 ohms closed and about 40Kohms at wide open throttle. does that sound about right? i'll have to see tomm what the new TB measures.
i also got a surging idle air plate attached. we adjusted the screws a few times for the idle but we probably made a mistake in doing so. i'll take it off and run without it for a while.
i'll go at it again tomorrow.
 

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Discussion Starter · #8 ·
ok. i set the TB voltage to .98V. the red wire measured 5.03v which is good. i started it and it idles fine cold, and it surges when warm. the check engine light is still on and i didn't drive it long enough to see it turn off. the turned the surging idle plate all the way in to act like it wasn't there and it didn't get rid of the check engine light. i tried backing it off a bit but still nothing. i disconn the neg from the batt for a few minutes to reset the computer but it didn't go away. i emailed cnc-motorsports tech and the dude said that the TB resistance reading should be about .7 or .8 closed and 5 ohms wot. i measured about .7 closed and 3.33 open. i should get an email back soon about it. i'm stumped. i couldn't find the computer wire that runs along the fender. this was happening before i put in the new TB and EGR, but with a cracked distributor module and no check engine light. i have full rpm range when it runs. now the throttle dies sometimes, the check engine light is on, new TB, EGR, module installed. everything else is the same. dunno, either.
 

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Discussion Starter · #9 ·
i got myself a actron code scanner CP9015 today. i finally found the plug and hooked it up. i think i did it right, but not exactly how the book said. but anyway:
KOEO - i got 4 steady single flashes equally spaced (i'm guessing for V8 engine ID?) then a long pause and a single flash and another long pause and then 2 9 6 6 8 7. i'll decifer that as 29, 66, 87 repeated twice. no seperator flashes, so no Continuous Memory???

it said something about checking the timing but i think i'm set at 18 degrees so i skipped it. i'll check it again and get back to you on that one.

KOER - had no engine ID flashes but went straight into 9 8 6 6 9 8 6 6. i was surging before i put it to TEST and after it registered it spiked to 2500 rpms and sat nicely at 2000 for the codes. i'll decifer that as 98 and 66 twice.

is that a good diagnostic? i'll be back after i check my VSS, clean my MAF, check for blown fuel fuses, and probably clean my right o2 sensor. i think i'll clean my IAC for the hell of it too.
 

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Discussion Starter · #10 ·
i cleaned my MAF and IAC. i installed my Aeromotive Fuel Pressure Regulator and put a fuel pressure gauge in place of the schrader valve and bumped it to 43 psi. the idle is still kinda jumpy but the throttle (when it works) it super sensitive.
KOEO 31 31 1 29 66 87. i accidentally broke the vaccum line that goes to the EGR (silly me).
KOER 98 66 98 66 still. i didn't get to check the VSS or fuel pump fuses or right side O2 sensor.

that fuel pressure regulator was a pain in the a$$!!

i have the stock MAF. would the check engine light turn on because i have 75mm TB and EGR and not MAF? would that in any way be related to my throttle dying?
 
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