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Hello people this is my first message so bare with me.
I own a Hyundai Accent 2001 model 1.3 l gas G4EA engine code Europe.
The problems with that is that there is poor idle,there is a P0300 and a P0301 pending codes.Usually it needs to be cranked two times to get started.While on the road there is no problem no hesitation but when stop and idle sometimes the MIL blinks because of misfire code.Also when on the road with small speed about 20km/h if i let car just roll and put neutral i sometimes see engine RPM increase about 100-150 from idle,like something moving and giving false input to the ECM
I used to be something like a parts changer but no more.I have changed plugs and wires(bought it used so i would do it anyway) also replaced a maf which was faulty indeed(there was no singal from the maf ,didn't check the wire integrity back then so maybe a bit lucky there.)
Also replaced IAC(thought that maybe was the moving parts giving me RPM change when rolling with neutral) no difference at all.
Changed the ingition coil as well cause i was getting a bit of hesitation at rapid open throttle,maybe i fixed something there.
Today i messed the TPS.
Backprobing the sensor got all right 5v reference,ground and signal 0.4v at rest
Put the pedal all the way got only 77% on my scan tool and 4.2 volts of signal
Jumped the 5v to the signal and fried the ECM(kidding...).
Jumped the 5v to signal got 5v from my DVOM but only 93% on the scan tool.Do i need a TPS?
Also the STFT looks good + - 5% at idle but when accelerating i get even -15% meaning running rich.At that point i would like to measure fuel pressure but need to make a modification cause no schradder valve.I suspect a bad fuel pressure regulator as it is high rank in the manual troubleshooting with the symptoms of difficult to start and rough idlle and the Fuel trims I get.
LTFT around - 9%
O2 sensor before the cat looks good 0.1-0.7 v
O2 sensor after cat 0.4-.0.6 v
The injectors sound good,they all have the same rythm when putting a long screwdriver on them.
Also the timing Advance looked strange to me i got around -3 degrees at idle(manual says 9 + - 5 degrees) but looked good at open throttle.
can you adjust your TPS?, I would set it to 0.5v at closed throttle, make a note of the voltage its set to right now to put it back if need be. If the throttle butterfly is caked in carbon it could be at closed throttle at 0.4v, and after cleaning could be lower than 0.4v. Seems like the range is far out, you should see 100% at full throttle, theres no floor mat stopping it from fully opening? is there a throttle cable on the car?
According to service specs at idle there should be 0.1-0.875 V and 4.25-4.8 V at WOT.
I don't really rely on these cause i've seen different values for different causes.I think the TPS is ok cause i get in open loop condition at wide open throttle so for my ECM seems that 77% is ok to understand where the throttle butterfly is.(No mat interference,throttle butterfly clean,cable adjusted right)
If i move the TPS so as to get a reading of 0.41V i get RPM increase and i'm at 1% at the TPS reading,so i stay somewhere in the 0.37-0.39 V at idle.
Something that came to my mind is that maybe there is an air restriction and that's the cause of getting negative fuel trim.
There is a screw at the throttle body that is preset from the factory and the manual says DO NOT ADJUST.
I adjusted this made a bit mess cause didn't got a reference point but now i put everything to where it was and the car is working like before touching it.
By screwing this i get a MAF g/s air increase.Now i'm at about 2.75 - 3 g/s,the manual says between 2.5 - 3.3 g/s so i'm going to put it to the max reading while i'm still at 0% at my TPS so as to allow more air to pass through and see what happens there.
Update
The MAF air flow was put to approximately 3.25 g/s screwing the bolt at the throttle body.Idle RPM at about 830.The TPS mounting holes where widened a bit so i could adjust it and now it's output voltage at idle is 0.35 v, i get a reading of 1% of TPS position at about 0.37-0.38 v
The car runs a bit better i think but will see how it goes and if i still get a P 0300 code.
The problem seems to be created by the after market MAF that i have put on after i bought the car.It definitaly didn't make any fault codes but it is not calibrated well for my car.Was found through ebay and looked good according to codes etc.
The fact is that the car has problems only at idle.I measured again the voltage reading and it is around 1.6V way higher than what is recommended for my car which is 0.7V - 1.1 V thus giving a false load signal to the PCM to add fuel and then trim it back as it see rich O2 sensor and that's why i have negative 10 LTFT
I tried to calibrate it through the idle screw at the throttle body but no luck.I could only get it down to 1.54V
At snap throttle i managed to see 4.2 with my DVOM,i'll try to clean to see if it may change something cause dirt sometimes can cause better cooling due to bigger diameter and air turbulence at idle.
The MAF was finally replaced and the readings are normal,the voltage was similar to the after market but it seems that the OEM is calibrated as it is supposed to.
The LTFT is at 0% and the STFT is fluctuating +-5% most of the times.
The problem was found and it is the valve guides are worn and possible one or valves are not closing right,a simple vacuum gause was used,see the video
The car is not fixed yet but as i'm still watching and learning i think that there is a possible input problem or a wiring problem,as i've heard some relays and maybe injector clicking with KOEO.
Maybe a worn Crank sensor not producing a good signal at idle causing the misfires but producing a good signal while RPM rise.
Further test will be done for sure.
