Car: 00 AP1

Problem description:

Car bucks at low throttle input under load and idle weird (revs up and down between 2k and 1k) somtimes on startup or on a hill.

Another noticable thing is this, i tried putting car in neutral, and depress the gas pedal ever so lightly and hold it there. the engine would respond (by reving to a certain rpm point) and then slowly revs down until it almost dies out, and then it'll rev back up and it'll slowly die down again and it goes on until it settles at a very low rev. Then i let off the gas and the car would stutter and revs back and stay at 1k. sometimes it would overshoot 1k but eventually it'll get back to 1k.

my radiator fan is constantly on whenever the key is switched to the "on" position.

Engine sounds rough, sounds like a diesel but not as loud as one. and i get lots of black soot on bumper

mods:
intake, header, ap2 exhaust (as far as i can see, bought the car used, don't see any other mods)


things i've changed out:
map, spark plugs (used the correct ones as taught by s2ki members here), and PCV valve.

it's frustrating me quite a bit, it does it at low/part throttle inputs. but it doesn't seem like it has any problem with full throttle acceleration.


Thanks in advance for the helps!!

 

TPS?

 

Have you tried resetting the ECU? That would be the first thing I would try. I had similar problems to what you are describing in which my car (MY00) stalled traveling at 60 km/h after I let off the gas pedal clutched in. After blipping the throttle my RPM's would drop a bit below 1k and the car would feel like it's about to stall. I reset my ECU and followed the proper ECU idle re-learning procedures and all my problems went away. My problem surfaced after a massive temperature change from the last time I had the car on and the time I was driving.

As for the black soot on your bumper, MY00-01's are known to run rich and it's normal (it occurs on my car too).

 

yea forgot to say i did the ECU relearn a couple of times already, but it comes back after maybe 100km

i thought it might be the TPS as well, so i bought another throttle body to see if it'll fix the problem. i might try that this week.

my fuel pump was making high pitch noise the other day, it seemed to have gone now though.

this car is frustrating me because it doesn't do it all the time, just when it likes to act up, it acts up.

also, when i blip the throttle very quickly, the car bucks like hell, so i need to drive with very smooth throttle inputs to not upset it. I'm really hoping it's just the TPS sensor being screwed. i'll update later this week after i changed out the throttle body

 

changed out the throttle body...

so the car responds better now. but one tiny problem remain.

when i try give quick small inputs to the throttle more than 2 times, the car would jump a lot and it feels like the engine is gonna pop out and die. but if i give it steady input, then the car would feel momentarilly a power loss but then power will come back after a second or 2.

and on initial startup, the engine makes a squeak sound that last no more than 2 seconds and it go away. on cold rainy days, the idle does not settle until the bar reached 3 on the temp gauge.

i dunno what else i need to change out, i've done most of the basic ones already...

 

move 2 under the hood

 

sounds like an injector is sticking or either your fuel pump is giving up the ghost.

 

had the same thing on a accord, it was the idle control valve, idk if the s has it but if it does try cleaning it