bogs and idle search

[mvs2]

Thanks a lot for all the help guys I appreciate it.


After the car warmed up I revved the engine to 2k rpm and held it there, to my surprise the rpm started going nuts like when it dies on me. The rpm sits at 2k then drops to 1500 and back up to 2k over and over -- this only happens when I held RPM at 2k, if I revved higher it was fine.


I'm not sure if that information helps bu definitely interesting see that I can cause the rpm to go bonkers. When this happens while driving the rpm does the same thing but I have no throttle response.


Does this sound like a possible O2 issue? The meth should be out of the tank by now. It seems whatever is causing the problem is " dying " quicker now as I can't seem to get too far without the problem happening.

[Skym]

Unplugging o2 sensor should tell you that it's the cause, but if engine is running lean, could result in engine failure (need to check with wideband afterwards).

I'm thinking engine could be running lean for some reason (fuelpump failing, intake manifold airleak, methonal fuel, misadjusted TPS, etc) and o2 sensor adjusting to it. Fuelpressure check should eliminate fuelpump, fuelfilter, etc. Wideband helps to eliminate intake manifold leak (would run very lean at idle, etc). Running fresh fuel should eliminate the methonal.

Also could be leaking / damaged injector. It's a process of elimination.

[mvs2]

Unplug the o2 sensor and do the same 2k rpm test?

I think the meth in the fuel should be alright now its been diluted with 3/4 tank fill up and a 1/2 tank fill up. Even when he put the meth in there was only a 1/4 tank and it ran alright, he said he didnt notice any bogging or anything and I didn't notice it till the next day as well.

I have a digital gauge in the car that reads the Injector duty cycle, Afr ( but its not proper I was told ) engine temp and speed.

When I hold the rpm at 2k the injector duty cycle goes to 5% then when the rpm drops to 1200 or so the duty cycle goes to 1%, makes sense seeing how the duty cycle is going to be less for the lower RPM I suppose. Like you said its a matter of elimination.


If it were the fuel pump I would imagine the RPM issue I had would happen when at any RPM range? Its just odd that I can only force the issue by opening throttle to 2k rpm, unless otherwise driving.

[jinglebell17]

I havent read the replies to this thread but based on what your original post is about, I'd say take your MAF out and clean it. Use a long skinny pokey stick and poke through a hole in the screen and carefully get the gunk off the sensor part on the inside. If that doesnt work then unplug your AAC valve on the back of your intake manifold with the car running and see what happens.

[Skym]

Unplugging o2 sensor stops it being a cause of the up and down rpm problem. But it's probably compensating for something which worries me.

On my car, just unplugged o2 sensor and checked with wideband and was ok, reset idle, reset TPS (later on after realising it was adjusted wrong). But if fuelpump is on the way out, unplugging o2 sensor is not a good idea (I was warned to not unplug o2 sensor when there's a faulty fuelpump, so check fuelpressure first, check with wideband).

Only way to make sure the methonal is gone is to drain fueltank properly into a barrell (can get a barrell with a hand driven pump on top to drain fueltank) and refill with fresh fuel from a couple or more fuel cans (depending on how many litres they are) to get to service station and then refill with gas at service station.

Cheap AFR gauge would be using stock narrowband o2 sensor (0-1V). Wideband is 0-5V and has it's own gauge (option), etc.

The duty cycle drop is probably the decel fuelcut, fuel recover that kicks in around that rpm or o2 sensor voltage has reached the go lean voltage trigger on ECU thus ECU making engine go lean again so revs rise. Without datalogging, looking via Nistune, hard to say which it is.

Also could be voltage to fuelpump. Usually voltage to fuelpump drops with light's, aircon, etc on (by turning those auxilaries on, you could test that I guess). But would notice engine going lean at higher rpm.

It's worth checking everything that it could be, as sometimes you find other problems that need to be sorted.

[mvs2]

Well guys it looks like the culprit has been found.

Last night we checked the fuel pressure and it was solid, however upon close inspection I found that all 3 o2 sensor wires had been " crushed " quite badly and were all barely hanging on by a thread. We disconnected the O2 sensor with the fuel gauge on and the car ran like a champ. With the o2 sensor plugged in it bogs.

So the o2 sensor has a replacement on the way !

[Skym]

Good to hear that you found the problem.

[mvs2]

I need to stop posting every time I think the problem is solved. On the way to work today I didn't let the car warm up fully and it took only 30 seconds of driving before it started bogging and a stalled on me. After I let it warm up it ran fine.

After work I let it warm up so the needle was at mid point and it ran great all the way home.


Wonder if this is just a whole other issue with driving the car cold. if it starts causing problems while warmed up fully then I'll be going after a new maf

[Skym]

Check that TPS is set on idle contact. If TPS is not set on idle contact, the engine can drop below idle rpm (ECU doesn't kick rpm up when backing off throttle while slowing down, switch to idle tables, etc) and might make engine stall when engine is under load (up a hill, with auxilaries, light's, etc on). Sometimes doesn't put a TPS error code on ECU until TPS is really out of spec with voltage. The last TPS failure on my car was like that.

[mvs2]

Hey guys,

So as you know i've been running with the o2 sensor disconnected and its been running good as long as i let it warm up 100%. Today I went to start the car after it had been sitting for an hour or so and the RPM started bouncing from 1k-2k over and over. I tried giving it some gas but it wouldnt let me rev over 2500 rpm. After a few tries it stopped bouncing idle and was alright. After it had been idling for a bit it would randomly shut off, not slowly dip in idle till dead, it would just shut right off and fire back up.

I called my friend who I bought it from and as soon as I told him what it was doing he said its the MAF. Tomorrow hes going to bring a new MAF over for me and we are going to see if that resolves the issue. I cross my fingers that this will resolve the problem

[Skym]

The rev limiter part sounds like MAF failure. Should be a MAF error code on ECU.

The high idle around 1500rpm when warm, MAF error code on ECU is what happened with first MAF failure on my car (engine didn't stall, idle bounce, etc) and MAF was unrepairable. MAF failure can be due to using the wrong cleaner that damaged the hotwire or the soldering is really bad on circuit board to plug, etc inside square part of MAF that it did some damage to circuit board, etc (New MAF on my car had no bad solders on circuit board, etc inside square part of MAF).

[mvs2]

I sure hope this fixes it. will find out shortly !


Also forgot to mention my gas mileage is freaking terrible. I've got under just under half a tank and that has got me 105kms so a full tank of gas would get me about 200kms

Im really thinking this maf will resolve the issue.

[mvs2]

working maf is in now and so far so good !