Idle Problem: trouble maintaining Idle + jumpy Idle

[gordonliu]

Here is the problem:

after the car has NOT been driven for a while (a couple of days) it will start fine, and drive fine for a whille.

after it has been driven for a while, and even after stopping and letting it sit for several hours:

the car will die at idle OR it will drop to a really low RPM (300-600) and then jump up to ~1100 (near where it usually idles) and then it may drop down go back up, etc (I imagine the behavior as "finding" the idle)

after it has been driven for a while, it may not start:

the engine will turn on for a moment and rev up to ~1000 RPM then die instantly

I can keep it going by holding the gas pedal for a moment and maintaining the revs above the idle for several moments, after which it can hold the idle.

there is NO other odd behavior. it runs fine, holds and releases boost fine, etc.

STATS:

1990 coupe chassis

blacktop SR ~ 40000 miles (~60000km)

SR ECUSR MAFgreddy suction kit

Nismo FPR (stock rail)Fuel pressure (analog) = ~37 PSI at idle (i have checked the range, it is fine)

STOCK FUEL PUMP (ka24e fuel pump)

FMICcheap Ebay BOV

profec b

possibilities (in my opinion):

IACV problemBoost leaksensor issue (loose/shorting/broken sensor)FPR

fuel problem - low pressure is a possibility with the stock fuel pump

I have the CEL wired, and it will light when the car dies, but turns off when the car runs. Im pretty sure it reads code 55 (i thought this code was not an issue?)

BASED ON THE STOCK FUEL PUMP, I AM GUESSING IT IS A FUEL PRESSURE ISSUE OR POSSIBLY THE IACV. I HAVE NOT EXTENSIVELY CHECKED, BECAUSE IT IS NOT A HUGE ISSUE, BUT I WOULD NOT LIKE TO DESTROY MY CAR BY RUNNING IT WHEN IT HAS A PROBLEM.

let me know if you have any input. thanks in advance

[jetblack24]

I had a similar problem. Turns out my blow off was a bit loose and letting out air on idle. I would do a vacuum test first. And definitely get rid of that stock fuel pump!

[gordonliu]

yeah, its these old cars and these god damn f***ing aluminum fuel tanks.

the last owner/servicer must have tightened the bolts on the gas tank cover...

the bolts were stripped INSIDE THE f***ING HOLE. so basically they just sit and spin.

they do not come out.

impact wrench

impact gun

PUSH SUPER HARD

PULLING SUPER HARD

nothing

I had to pry the mother f***ers loose by jamming a screwdriver under them AND THEN unscrewing.

going to get a new tank from frsport.