Help - Engine idle rough and revs not smooth

[Philip Lee]

hi all,

i have been \"de-modding\" the car for the last few weeks and below is the sequence:
2 weeks ago - extractor and cat back;
today - AFC and Loch Stewart CAI.

there were no problem after the exhaust was back to stock. i have been driving everyday during the weekdays and all was fine.

this morning i took the CAI out and put the stock air box in and took the piggy backed air/fuel controller out. i only disconnected the -ve on the battery tho. not sure if it would effect anything. started up the car and it seems normal until i reversed it out the driveway. idle started to swing between 600-1000rpm constantly, i squeeze some throttle slowly and immediately the rev bounced to 600rpm then back to 1500rpm and the engine/gearbox started to vibrate and revs very roughly and runs very rich.

so rechecked under the bonnet and everything seemed fine. restarted the car and the same thing occured so i thought i should drive the car a bit to let the ECU adapts. the car ran very rich. i could see black smoke in the mirrors starting from 2000rpm up and the car revs very slowly. after 15mins and no change i decided to go home and unhooked the battery to reset the ECU (both +ve & -ve).

90 mins pasted, hook up the battery again, started the car and same thing happened.

anyone has any suggestion? my car is NA6 and has short nose crank but i'm sure the crank is fine. would it be AF meter? O2 sensor? spark leads? any other suggestion?? i'm a bit lost because it drove smoothly last night and apart from the CAI and AFC i didn't touch anything else.

timing belt was changed 10000km ago by JAK. NGK irdium plugs were done the same time. engine oil and filter were changed in August with Mobil 1 5w50 and OEM filter.

thanks in advance.

Philip

[AJ]

you didn't break a wire or pull a connector off anywhere while you were removing stuff??.....just a thought.......someone was having o2 sensor probs that sound the same as yours.........maybe you accidently pulled or broke a wire off??........

[Philip Lee]

thanks AJ.

i checked the o2 sensor connection and it seems to be connected fine.

i also replug the airflow meter plug too.

would o2 sensor fails in a sudden or graduately?

cheers
Philip

[JBT]

...there were no problem after the exhaust was back to stock. i have been driving everyday during the weekdays and all was fine.

this morning i took the CAI out and put the stock air box in and took the piggy backed air/fuel controller out. i only disconnected the -ve on the battery.....

It sure sounds like it was something you did removing the last two items - it would be a huge coincidence for something else to fail at the same time.

Have you tried bridging the TEN and Gnd terminals in the diagnostic box and checking the base idle speed? Does it idle steady with those terminals bridged? The ECU resets if you disconnect the battery.

[Philip Lee]

thanks JBT. i hope it's something i overlooked rather than something failed.

i haven't check the base idle. but i don't think that would cause the engine running rich and rough.........

i have disconnected the battery for over night and see how it goes tomorrow. tomorrow morning i'll start with the idle then maybe putting a pod filter back in and see if that makes a difference. then will try to swap spark plug leads etc.

i doubt very much it's the ECU wiring as i checked again this afternoon. there were only 4 wires to hook up with my AFC, power/ground/airflow and rpm. it doesn't seems this area is the cause.....

[ampz]

Vacuum leak?

I thought an AFC would need more wires for it to modify your fuel (and/or timing).
If it controlled your timing and fuel, then the base setings on the engine would be way off to fool the standard ecu, hence it running a little funny.

Unless the AFC was just monitoring your fueal and air.

[Philip Lee]

thanks ampz



the above is taken from the installation instruction for NA6.

as u can see only 4 wires - airflow/rpm/power/ground

it doesn't change timing. it only changes the fuel setting per rpm.

tried the gnd/ten trick but it's not the cause. rev is still strange as before. it seems when i slowly revs to 1500rpm from idle, the revs quickly dropped back to idle and u need to put more gas for it to increase again. once it got up to 2000rpm, there are lots of black smoke.

i will double check the wiring again. maybe something is wrong with the rpm wire.

how can you check on vaccum leak?

thanks

[Philip Lee]

triple checked the ECU wires again and it's 100% right.

put the CAI back in, and still the same problem.

so it seems it's not directed related to the \"de-moding\".

would ECU gets damaged if i didn't unhook +ve battery terminal?

maybe the AF meter is stuffed??

the search continues.....

[JBT]

Reconnect the piggy back FC back as well and see what happens.

[Philip Lee]

Reconnect the piggy back FC back as well and see what happens.

oh this is something i really want to avoid cos it's a PITA to connect.

i guess next step is to swap with my fd's AFM and ECU and see if that helps.

[Philip Lee]

thanks carsokay.

i have redone the AFM to ECU wire and it's working. i tried to start the car with the wire connected (runs rich and rough) and disconnected (dies immediately). so i think the connection is there but something along there is obviously wrong.

i'm thinking if i short anything while i cut the wires when the +ve was still connected. and if this is the case, what can be damaged. i only cut off wires for power/ground/rpm and AF.

still lost....

[NMX516]

Is the afm fitted the correct way around? If the flap in the afm can't swing open, either because the air is being drawn through the wrong way, or because the meter is installed upside down, you will get the sorts of problems you are describing.

[Fatty]

Is the afm fitted the correct way around? If the flap in the afm can't swing open, either because the air is being drawn through the wrong way, or because the meter is installed upside down, you will get the sorts of problems you are describing.

my afm is installed upside down, i have no problems at all.

[NMX516]

Lucky you

It can be a problem for some vane type afm's, but not all. Maybe it's not an issue for the NA6 ones.... Basically gravity can be the killer, so at low revs/low engine load, the afm vane can't be moved accurately or adequately to give a correct reading. The spring can be too stiff, then combined with the weight of the vane assembly a small air mass struggles to move it enough. I had this problem at one time with my Pulsar.

[Fatty]

i guess it would be a problem depending on if the flapper is hinged on the side or the top / bottom, coz of gravity as you said. i see how that could happen. maybe the na6 one is hinged at the side, hence it wouldn't matter if it is upside down.