idle problems, fixed :D

[undecided111]

today I was checking error codes because the spark plugs have white on them and I heard it could be running to lean and that it should come up with a error code so I check and nothing so I unplugged airflow meter to see if what I was doing was right and it came up with airflow meter error code so to clear the ecu's data I unplugged the battery to reset airflow meter error code when I plugged it back in the alarm is now working and didn't before but now the idle goes up and down between 200 to 850rpm I can rev it and hold it at 2000 or what ever but when I take my foot off the gas pedal the revs will go back to 100rmp and sometimes it will stall out, any idea what could be wrong ? it was ran fine before I unplugged battery

[marcellarius]

It sounds like the ECU's closed-loop idle control isn't doing its job.

Unless you had 'idle droop' problems in the past (not uncommon, some people mask with the mechanical idle adjustment) then I'd look at things that you've disturbed when testing things.

Make sure the AFM is properly plugged in, and that the wiring harness hasn't been damaged when pulling it out -- perhaps there is a bad joint in it and the ECU isn't getting a good signal.

Ensure that there are no air-leaks after the AFM, this could be the case if you removed a vacuum line or removed the intake tubing

Does the car do this when the engine is first started? -- the AFM will mostly affect fuel trim I think, and until the car is held above about 2000rpm for about a minute, the fueling will be open-loop and running rich until the O2 sensor is hot enough to give sensible values.

[undecided111]

its almost like it has a huge exhaust leak on start up it will go to 800 then down to 200ish then to 800 then 200 then 800 then stay there and idle fine if you give it a rev it revs fine but as its coming down in rev it goes down to 100 or 0 and almost stalls there are no vacuum leak iv cleaned the air flow meter sensor double checked for exhaust leak and nothing checked all spark plug and they are fine, all I did before the problem started was check error codes with a led in the dyno plug so nothing was touched I took the positive battery lead off to reset ecus data on the error codes and then all this happened

[marcellarius]

The standard ECUs don't 'learn' so it won't be something like that. (at least on the pre-OBD 2 NAs, not sure about later)

You haven't accidentally left a jumper wire between the TEN/GND pins in the diagnostic connector?

My car has idle droop problems; I got in it one morning and every time I let it drop to idle in traffic it would almost stall. It was still happening later that day so I opened the idle control screw a bit so that it would hold at 850ish. I have no idea what caused this, I hadn't changed anything. My best guess is that perhaps my alternator was putting more load on the engine and the idle system was having trouble correcting for the extra load?

I have other driveability problems that I've put off diagnosing -- slight misfire at idle, but I suspect it could be related, perhaps a vacuum leak, bad O2 sensor or something. No codes.

[undecided111]

I found a thing no the net which I tried it was this
1) Make sure that the engine is warm, but not hot.
2) Turn off all electrical items (fan, radio and lights)
3) Start the car and after it settles into a regular idle notice where the needle is on the tachometer. It should be just over the graduation mark below the "1". (around 850/900 rpm)
4) Bridge the TEN and GND cells
5) You should notice the idle speed change after a few seconds.
6) Have a look at the tachometer. If the ambient idle speed moved then you have discovered the problem.
7) Slowly turn the idle screw until the revs come up to just over the graduation mark on the tachometer.
Do this slowly, as there is a slight lag in screwing and response.
9) If the radiator fans come on during the process then stop adjusting and wait for it to go off.
10) When you have it idling where you think it should be remove the bridging wire. In a few seconds the ECU idle setting will kick in. If the engine remains at the same rpm then you have matched the ambient idle to the ECU setting.
11) If not, then replace the bridge and adjust the idle screw,
12) Repeat steps 10 and 11 until the idle speeds are matched
its running a lot better after doing that its now sitting at 950 rpm at running temp it has a slight shake ( misfire ) and dips to 900sh when left to idle for about 30secs which is what it was doing before so not sure what happened

[marcellarius]

Unfortunately, that's covering up the symptoms rather than fixing the problem hopefully it keeps the car driveable, but from what I've read it will possibly happen again and eventually you will run out of idle adjustment..

[undecided111]

yeah well im hoping it doesnt im going to be replacing o2 sensor and a few other things this coming weekend because im not sure if anythings ever been done so hopefully it fixes the problem but atm its drivable

[marcellarius]

Keep me updated on how that goes

My 94 1.8 has had similar problems since I bought it. I've done plugs, leads, air filter, fuel filter, checked for vacuum leaks (nothing that I could find signs of with water spray or carb cleaner).

Next things on my list were O2 sensor (the exterior looks fouled up, had some power-steering fluid overflow onto it) and clean throttle and intake manifold, idle air control system, replace gaskets and fuel injector O-rings, check exhaust headers for cracks etc.