kindafast

hi. This morning when I started my car it shaked and the rpm jumped around from 500 to 1500. I shut it off and restarted. Worked fine. Then a Few hours later I started it again and the rpm shot up to 3000 and eventually went down to 1500. Standard idle is about 700. So I shut it off and restarted it 4 times until it started normally. My dad will take the car away from me if it breaks again. My parents think I always brake it somehow LOL. Please give me some ideas as to what this might be.

Eurocharged Canada

That is the cars way of warming the cats up. It's emissions related. Let it sit there for a bit.

ScottW911

Mine has done this for a year or more now, although, at more consistent rpm's. When the car is cold at start, it will go to about 1500 rpm for about 20 seconds. It will then drop to the usual 750 rpm. As long as the Cat is warm, the car starts at 750. I heard that this develops over time as the Cats get coated inside and take longer to warm up.

It should not be a major concern to you.

trbo2nr

Nice to know as mine did this too- not that long ago. Thanks for the info.

kindafast

No, I know that it goes up to 1500 after being off for lots of hours, but it wasn't normal today. I think my other cat is going out.
I let it idle when it started at 2500rpm then it went down to 1500 and stayed there for 30 secs. So i kept shutting it off and restarting and everytime it did something different that wasn't normal. On one restart it kept going to 3200rpm's and then dropping to 2000 and raising again as if it was reving, I checked the gas pedal and it was all the way back, popped the hood, restarted it again and it went back to normal.
Before my first rimary cat went out the car had the same symptoms about a month prior to engine misfiring.

Thanks for the replies though!

kindafast

Could "NOS" fuel booster cause this? I split the bottle last two times I filled
up.
I'm thinking about pooring techron in the tank to clean the fuel system up. Could it have any negative effects on the car due to using this after using a fuel booster?

SeeKlasse

techron is the safest fuel system cleaner. if you didnt "overdose" on octane booster then the problem shouldnt be from that. unless, of course, you used half a bottle of NOS octane booster on a full tank of regular gas, which would take it from 87 to 88 octane probably. in which case you need to raise the octane level bc the car could be altering the ignition cycle to prevent pinging or knocking


NOS booster is MMT based and wont harm exhaust components unless you use alot of it along with premium. the case may occur where your octane rating is so high that detonation doesnt occur in portions of your mixture, and then the rich fumes are dumped into the exhaust, causing potential harm to cats and o2 sensors.


do your best to eliminate the fuel system from the list of potential culprits. finish your tank off and fill it up with chevron premium. you can even put a bottle of techron in there if you wish.

back when i was 17 my parents gave me a c280 (w202) and whenever anything broke it was my fault. as far as they were concerned cars didnt break unless you abused them... i chuckled when you stated that your dad would take your car away if it broke again lol. you should feel lucky that youre driving a c32 at that age!

kindafast

You don't know how lucky I was when I saw it standing in the corner of a parking lot. Me and my dad went to a lot to look at some mustangs and 330's and I liked this black new style Mustang GT. But on our way out I saw a C Class in a corner that looked agressive, I thought it was one of the workers' cars at first, haha man you won't believe how happy I was that it was within budget when I saw the price tag and the AMG badge. I knew then I didn't wana look at anything else and every car I had in mind vanished.

You got quite a car there yourself. Anyway thanks for the tips!

c32used