180sx Rough Idle And Bogging At Partial Throttle

[Bvarnon]

So my 98 180sx with the sr20det is having a issue, cold start it idles fine but one warmed up the idle begins to hunt dropping to about 800 and then revving up to 1200 before settling at 1000. Also at partial throttle while driving in any gear it bogs and right before it gets into boost it basically looses all power until I push the throttle more and then it goes 100% fine. Now the kicker, when I take the car on the interstate and get up to about 140kmph or about 85 mph it clears up and will run fine at any speed until the car is turned off. If turned back on even right after I turned it off the bad idle and bogging issue is back. Not sure what this could be but I do have good vaccum at about 22, plugs are changed and gapped, new coils, new maf sensor, i have no cel or codes, i have a new maf sensor wire on the way, tps has been checked and is at a good voltage. Fixed after ton of boost leaks and vaccum leaks not too long ago and left the battery disconnected so the ecu could relearn the car. Overall completely lost.

[PapaSmurf2k3]

Hi, welcome to NICO.
When you pulled the plugs did you take a look at them to see if they look normal? It almost sounds like you are running lean at idle. Do you have a way of monitoring fuel pressure?

[Bvarnon]

Hi, welcome to NICO.
When you pulled the plugs did you take a look at them to see if they look normal? It almost sounds like you are running lean at idle. Do you have a way of monitoring fuel pressure?

Thank you! Not 100% sure if this is how you reply, but yes the plugs look great. No i don't have a way to check afr but what gets me is that after driving it like the post says it will idle fine until turned off. I was thinking maybe iacv is getting stuck or maybe has a lot of buildup and when driving it becomes unstuck until I turn the car off again. Haven't had time to check it yet though.

[Bvarnon]

Update, pumping the brakes makes the car nearly stall. Pretty sure this signals are vaccum leak but not sure where or how bec I've fixed all i could fine, holds pressure, and I don't see any smoke leaking when testing it. Maybe fuel pressure regulator?

[VStar650CL]

A punctured diaphragm in the FPR will usually bleed fuel back into the vacuum hose, so that's an easy check. Could be a pinhole in the brake booster diaphragm, too. Assuming the check valve is good, pump the pedal after shutting the car off. You should get at least 2~3 pumps before the pedal goes high and hard. If it goes hard right away then you know the booster is leaky.

[PapaSmurf2k3]

Pretty sure this signals are vaccum leak

That's what I was thinking as well.

A punctured diaphragm in the FPR will usually bleed fuel back into the vacuum hose, so that's an easy check. Could be a pinhole in the brake booster diaphragm, too. Assuming the check valve is good, pump the pedal after shutting the car off. You should get at least 2~3 pumps before the pedal goes high and hard. If it goes hard right away then you know the booster is leaky.

Good call.

[Bvarnon]

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[Bvarnon]

A punctured diaphragm in the FPR will usually bleed fuel back into the vacuum hose, so that's an easy check. Could be a pinhole in the brake booster diaphragm, too. Assuming the check valve is good, pump the pedal after shutting the car off. You should get at least 2~3 pumps before the pedal goes high and hard. If it goes hard right away then you know the booster is leaky.

Just tested and it feels firm after about 3 presses, also if I go 90mph on the interstate then stop at a light or what not and pump the brakes the idles don't drop, it idles fine, and there's no bog. Also the pigtail and maf sensor connector should come in today so I'll test that.