lancer

my car has high idle RPM ( about 2500 RPM) when i start the car, it go down after about 5 minutes idling (back to 900 RPM). this happen after i strip the Oxygen sensor on the header due to the header replacement so the guy at the local shop replace it by using the same wire on the sensor and hard wired with some old sensor and install it into the new header. at the same time i changed the spark plugs and wire ( bigger set) myself too.

the problem occurred after that so i'm not sure which one causing the problem, new set of spark plugs and wire or the used Oxygen sensor on the new header.

also i notice a dramatic decrease in the fuel consumption. i think i'm running about 12 to 14 miles per gallon after that. another problem is that my car after driving for about 15 minutes and part or stop at the red light, the idle is start to go up and down,(not smooth idling like it use to be before). and yes the check light engine is on permanently after the old sensor being installed, and flashing sometime when i'm driving on high way at high RPM.

can anyone have any idea what is going on. I personally think that it was the used sensor that cause the problem. or maybe it the old coil with the new wires and spark plug. please help me out guys. thanks alot.

epikeddie

I'm placing my money on the used O2 sensor. The car obviously picked up that the efficiency range of the O2 sensor was not adequate - therefore throwing a CEL light.

Go switch the sensor, reset the NVRAM following procedures, and try that out.

The coils and plugs wouldn't affect the fast idle speed.

Jedi54

iTrader: (7)

I think you should replace the 02 sensor.

what type of spark plugs? Which wires?


Sounds like your car is misfiring. Are you 100% certain that the plug wires at the spark plugs are properly secured? (they should click / pop when you fasten them all the way)
Are you positive you routed the wires from the coils to the appropriate spark plugs?

I know this seems trivial but it's always best to rule out the simple things first.


Also: you should get the CEL code pulled

lancer

i will check the spark plug wire (Moroso Spark Plug Wire Set) and the spark plug again( NGK Iridium for trailing and leading) today.

I pretty positive that i routed the wires from the coils to the appropriate spark plugs because i changed it one by one.

I will also order the new oxigen sensor today. should i buy a used one (12k) from one of the member on here. he has it for sale for $120 and he said it was working when he took it out of his car. the oxigen sensor for the header are so expensive. any place where they have it for good price?

lancer

would you mind letting me know the procedures how to reset the NVRAM.

Jedi54

iTrader: (7)

lancer: My personal opinion here...I'd spend the extra money and get a new O2 sensor. It could have been working when he took it off but if it's damanged in transit, you'll be back in this same boat.

I believe Expo1 found the sensors for a pretty good price. Let me see what I can find.

I believe the NVRAM is reset with the 20 brake pedal stomp procedure.

Jedi54

iTrader: (7)

Lancer: here's the ECU reset procedure. (see post 3)
https://www.rx8club.com/series-i-tech-garage-22/ecu-clear-reset-27548/

lancer

thanks alot jedi . i am trying to ask my friend to order the new oxygen sensor for me. he told me he can get it for 200 bucks. .

Jedi54

iTrader: (7)

you're welcome Lancer, I'm here to help.
$200 for OEM? Nice.

just as an added bonus, here's the order for the spark plug wires

lancer

another question!. the inconsistent idling is because of the failure of the oxygen sensor. is that right?

Jedi54

iTrader: (7)

sorry Lancer, only the 1st question is free.

Jedi54

iTrader: (7)

inconsistant idle can come from a few different sources.
I know I had it with a bad spark plug wire once but I wouldn't doubt that a bad O2 sensor could cause it as well.
the car would be getting bad readings and trying to compensate on false data?

lancer

i will use this order to check for the spark plug today. for the last couple weeks, i'm running about 12 to 14 miles per gallon ( worst than before changing the spark plugs, wires, and the header).

Jedi54

iTrader: (7)

unless you're redlining the car like crazy or are doing ALL stop and go, that mpg figure does seem a bit low. I average 17 mpg with mixed driving but I've got a heavy right foot.

Let us know how the spark plug inspection goes.

lancer

just driving like normal. i don't redline my car that often. i will inspect the spark plug and report it back later.( can wait to get home from work, still have another hour to go at work)

04RX8man

ok guys I guess we all can stop coming on the boards seems like JEDI has everything under control around here! haha.....

Jedi54

iTrader: (7)

lancer

ok, here is the results. i did check the spark plugs and wire. disconnected and reconnected again and make sure it was tight enough. check the routing too, and it was all corrected. turn the car on, the problem still exist. rough idle, idle go up and down ( not much, about 100 to 300 RPM, but with the custom exhaust that make it noticeable enough when idling). i'm runng 80 miles for .......half tanks of gas now.

for all that, i came to the conclusion to myself that,.....it was all because of the used oxygen sensor. so i hope after changing the sensor, it will be gone.

myriadshalaks

iTrader: (1)

is it possible something is screwy with your maf? maybe you've got a vacuum leak? I ask because i had similar symptoms when my secondary vacuum inlet was not capped tightly at the throttle body.

all that moving around in there, you may have broken or knocked off one of the hose parts. better check it before you go getting another 02 sensor, i would think.

also, i think you should reset your ecu if you haven't already. that will clear the cel at least temporarily. and it may clear up your problem.

but i don't really know much about anything.

good luck.

dannobre

iTrader: (3)

With no O2 sensor it will run in Open loop all the time........eating gobbs of gas

The O2 sensor is not a "normal" O2 sensor...you need to replace it with a proper unit the PCM can read

lancer

will replace it in the couple days. order for a new one today, and should be here in two days. hope will solve the problems.

lancer

I kinda have no clue what are you talking about. .....sorry. would you explain more.

myriadshalaks

iTrader: (1)

well, just troubleshooting.

you've told us you got a cel. you haven't told us what that cel is. have you read the code?

you also said the cel stays on. after replacing the stripped o2 sensor, did you reset your ecu? you didn't say either way. if so, can i assume the cel came back on after that?

everyone including you has assumed that since you did all this stuff with your 02 sensor and plugs that one or the other is what's causing your problem. And likely that's right. But what if you've presented a false dichotomy?

i have experienced similar symptoms as you. the idle would start out high. i got bad gas mileage. but the issue was not the 02 sensor. It was rather that the secondary vacuum was sucking in unfiltered air.

i am suggesting that in the process of changing the plugs and o2, you've inadvertantly knocked loose one of those lines that sucks air into the intake manifold. And that before you go out and buy something, have a look to see if that's the case.

lancer

would be a dumb question for you but... would you mind telling where is the secondary vacuum located at. i would check it if i know what , and where is it.

i did reset my ecu. the cel was gone for awhile and pop up right back. i didn't have a chance to read a code.

thanks for your comments.

myriadshalaks

iTrader: (1)

just check all the hoses on your intake downstream from your maf sensor.

the one that gave me trouble is on the underside of the throttle body which is the metal part in front of your intake manifold. if you're standing in front of your engine bay standing in front of it, you'll be looking in the top right corner.