Topic: Rough idle randomly

[1ofakind]

Man oh man. Always something haha. So guys I have a rough idle sometimes. I say sometimes because I noticed it usually happens more frequently when I'm at a quarter tank or less.. it sounds like it runs on 3 cylinders and shakes. My boost gauge vacuum is usually -19 and when this occurs the gauge climbs almost to -10. Now this only l happens for a few seconds while at a stop light. Once it's been a minute it will idle smooth and normal again.. if I pull away from the light while it's idling rough it Boggs and hesitates sort of and then goes smooth after getting to 10km/h

Then sometimes the car will have less power and if im cruising around maintaining one speed I can Hear the car missing at certain throttle positions. For instance if I watch the boost gauge right around -10 on the gauge it will do that under light acceleration.

What the crap is goin on. Front o2 sensor is what I thought but I have no clue, maybe fuel pump or fpr. I've spent so much time and money on the car i don't want to just throw stuff at it.

I do have a donor car I could swap fuel pumps to try maybe. Going to try swap the o2 as well for fun.

Any other suggestions??

[darthekai]

Could be fuel pressure. Do you have an AFR gauge? You would see it lean out if it was the fuel pressure or the maf sensor or potentially a clogged fuel filter (super easy fix, you should do this anyways).

Could also be missing due to loosing a spark. You can test your wires, test the coil pack, replace the plugs, check for cracked insulators, carbon buildup, etc. How old are the plugs? . Often the most noticeable spot for a weak spark is at high vacuum for some reason. Theoretically it should have an easier time marking a stronger spark under vacuum.


The climbing vac gauge at a stop light is indicative of an increased load on the engine or a decrease in power.
Check your power steering fluid levels, alternator charging voltage, try turning off high power accessories like amps, make sure your fans work properly...

[1ofakind]

Could be fuel pressure. Do you have an AFR gauge? You would see it lean out if it was the fuel pressure or the maf sensor or potentially a clogged fuel filter (super easy fix, you should do this anyways).

Could also be missing due to loosing a spark. You can test your wires, test the coil pack, replace the plugs, check for cracked insulators, carbon buildup, etc. How old are the plugs? . Often the most noticeable spot for a weak spark is at high vacuum for some reason. Theoretically it should have an easier time marking a stronger spark under vacuum.


The climbing vac gauge at a stop light is indicative of an increased load on the engine or a decrease in power.
Check your power steering fluid levels, alternator charging voltage, try turning off high power accessories like amps, make sure your fans work properly...

Thank you! I don't have a afr gauge, and my plugs are very new (5000km). I haven't done the fuel filter and have a funny feeling it's never been done by the look of it. Maybe I'll try a filter and pressure regulator since they are cheap. I do have the 02 coil pack conversion done.

So likely not a o2 sensor?

[darthekai]

An o2 sensor MIGHT make it idle a little faster or slower, but load wouldn't be effected and your iacv wouldn't be opening that much to keep it alive.

What's more likely than a stock fpr failing is the filter or a dirty maf sensor. I wouldn't throw money at a new fpr unless you're sure the fuel pressure is goofed.

Get some maf cleaner, and be careful cleaning the maf. Replace the fuel filter, Check the wiring on your coil pack conversion for rubbing wires, loose bolts, bad ground connections, etc.

[1ofakind]

An o2 sensor MIGHT make it idle a little faster or slower, but load wouldn't be effected and your iacv wouldn't be opening that much to keep it alive.

What's more likely than a stock fpr failing is the filter or a dirty maf sensor. I wouldn't throw money at a new fpr unless you're sure the fuel pressure is goofed.

Get some maf cleaner, and be careful cleaning the maf. Replace the fuel filter, Check the wiring on your coil pack conversion for rubbing wires, loose bolts, bad ground connections, etc.

I cleaned my maf not long ago just for fun when I changed my air filter. I have no way to test my fuel pressure. I could always try my ej20k fpr.. it's an sti so not sure if it's the same. I'm going to look it over later today

[darthekai]

you can check your grounds by checking ohms between the ring connector and the neg batt terminal.
Should be 0.5 ohms or less.

[1ofakind]

you can check your grounds by checking ohms between the ring connector and the neg batt terminal.
Should be 0.5 ohms or less.

Big help! Thank you!

[1ofakind]

you can check your grounds by checking ohms between the ring connector and the neg batt terminal.
Should be 0.5 ohms or less.

My ohms look to be 28-30??? Car was running should it be off?

[RockThePylon]

My ohms look to be 28-30??? Car was running should it be off?

Should be off. Touch the probes together as well to see what the meter reports for "zero" resistance.

[1ofakind]

Should be off. Touch the probes together as well to see what the meter reports for "zero" resistance.

I figured haha. Thank you. My grounds all seem good. Took the car for a spin today and ran great, I get a very intermittent check engine light that goes away faster than I can check it (sounds like it runs in 3 cylinders when it comes on) light goes off and then it runs awesome again. Probably got a bad coil pack..

[Coops1313]

You can put the black connectors together under the dash and it will give you morse code on the dash telling you the past check engine light conditions even if they are not present at the time. i would also take a look at the knock sensor. those are symptoms.

Cheers!