I reset my ECU and my car wont idle now!

[jinglebell17]

Ive asked questions about this before but I need an opinion ASAP.

I had some free time today so me and a buddy changed my oil, cleaned my MAF sensor, cleaned my HKS air filter, and my car was idling kinda funny afterwards.

It had done this before but only every once in a while. It would fluctuate between 500 rpm and 1100rpm. After cleaning out my MAF sensor it was doing it and wouldnt stop so we reset my ECU.

Now my car will not idle when i turn it on. The idle wants to do that fluctuating thing but its trying to do it from 100 rpm to 800 rpm. If I dont touch the throttle it will do it a couple times and then it will get lower than 100rpm and die.

One note Im going to add is I had a screamer pipe for a downpipe up until last night and I was too lazy to remove the oxygen sensor from the screamer pipe so I plugged the hole with a Cherry Bomb O2 Sensor plug when I put the new down pipe in. So it has no O2 sensor in it.

[cschepp]

I would plug the o2 back in and see how it works man. This is something to look at man......

http://auto.howstuffworks.com/question257.htm

[jinglebell17]

my boss told me when you reset your ECU that you should drive around for 10 minutes or so. I took it on the highway and drove 110km/h for a couple minutes, then 140km/h, then 160km/h. once I got about 15 km out of the city I turned around and did the samething. I got back in the city and came to my first stop sign and it stayed idling in between 300rpm and 1000rpm. i'll see what happens when I put the O2 sensor back in. I hope I didn't royally F myself in the A for resetting my ECU

[Skym]

Driving more just makes coolant hotter and takes engine ECU off the warmup tables which have a higher idle rpm and takes IACV out of the equation.

Rev needle going up and down at idle can be the AACV is not set at same rpm as ECU (650rpm for RB20DET). It requires Consult (Nissan dealership) or Consult program, cable if you don't know how to reset it via diagnostic screw on side of engine ECU. It can happen when you play with AACV screw without setting engine ECU (via diagnostic screw) in idle adjustment mode (had this problem in the past, was combination of failed TPS, incorrectly adjusted AACV and failed o2 sensor).

Gets worse when idle stabilisation tables on ECU adjust ignition timing - or + 4-5 degrees trying to stabilse idle which could cause engine to stall. In some cases too thick engine oil can be the cause or just add to the problem (found this out on my car by changing from 10w60 to 10w40 which reduced the hunting at idle, but comes back with airleaks).

o2 sensor is part of that process (rich makes revs drop, lean makes revs rise). Probably will make the idle problem worse if you reconnect it. Also airleaks add to the problem, which the o2 sensor helps to compensate for.

Also what did you clean MAF with? Should use CRC MAF cleaner.

[jinglebell17]

I cleaned my MAF with carb cleaner. it says on the can MAF sensor safe . I don't know how to adjust idle on these engines. I don't even know where the ECU is.

one question, on the side of the throttle body there's the sensor that connects to somethig else about an inch below it. I assume it's the TPS. I tapped into it with a volt meter and it would read 3, then 4, then 5, then 0 (not always in that order) while it was fluctuating.

when I leave the car sit for a half hour or an hour, I go start it and it idles fine, then if I leave it idle for 10 or 15 it will start fluctuating like I've explained. then it might stop for a bit and start again. I don't know what going on. it doesn't lack any power whatsoever, my car just wants to purrrrr like all the time

[Skym]

From what I understand, carb cleaner damages the coating on hotwire sensor, etc. Only use CRC MAF cleaner.

Engine ECU is behind the passenger side kick panel (under dash, just infront of passenger door). You need to remove plastic kick plate in bottom of passenger doorway via removing screws in the middle of clips that holds the clips in place and then pull kick plate upwards and it should unclip. Then remove the screws holding the kick panel in place. ECU should be mounted by a few bolts (be careful with loom when removing engine ECU). On side of engine ECU is the diagnostic screw and a light to flash the error codes.

TPS should be around 0.44mv or something like that at idle (touching idle contact inside TPS which makes engine ECU use idle stabilisation tables, etc). If TPS is not touching idle contact or is faulty, could be part of the problem.

With an hour, that's due to coolant temps cooling down and engine ECU using different part of warmup tables with higher idle rpm and IACV (cold idle valve that's used during engine warmup) is used to add extra air on top of what AACV (hot idle valve that's used when engine is warm and adjust idle rpm to 1000rpm when aircon, light's, etc are on) provides to intake plenum to combat the rich mixture when engine is warming up.

IACV = Idle Air Control Valve
AACV = Auxilary Air Control Valve

But it could be due to faulty alternator that was mentioned in other thread.