Unstable RPM when first starts the car

[andivic]

my car happened to have unstable RPM while starting the engine in the morning. First it goes up to 2500 rpm and down to 700 rpm "once" per second when first started, then it would stay around 1600 rpm, after a while it does the same thing again over and over until the car is warmed up. Another strange thing is I usually put the gear at neutral when stop in front of red light, normally the rpm will stay at about 700 rpm, but mine jumps to 1200 rpm when i put the gear in neutral. Do you think is there any problem with my car ? Is this the early symptom of the transmission failure ? (I have no idea if the previous owner ever done the tranny rebuild before, and my 1st to 2nd gear is not that smooth, the car shakes when it goes from first to second. Any suggestion ?

[vkykam]

Doesn't sound like a tranny issue if you are having irratic issues.

Check for things like air leaks along the intake after the MAF, or the MAF itself. When I found a crack on the air box above the throttle body, that's pretty similar to what you are experiencing.

VK

[Aredubjay]

There should be a certain ammount of "unstable rpm's" at start-up (perhaps not this extreme), but the ECU goes through a "self check" process every time you start the car. It runs through all the electronic sensors and such and adjusts the car to run according to the information it has gathered from them.

One thing you may try, is cleaning your throttle body. There may be buildup that is causeing your throttle plates not to close all the way. At any rate, that would be a safe and cheap start at troubleshooting.

[deligeds]

I've experienced unstable rpms during warm-up for a long time. I started noticing it around the time that I switched to a high-flow conical air filter, so I assumed that the MAF just didn't know what to do with all that air. Mine is especially noticeable when I climb a hill just after starting the car. Anyway, seems to be fine after a minute or so, and it hasn't gotten any worse over the past couple of years.

[EveryShadeofBlue]

I just installed a K&N a couple days ago and it started doing the unstable RPM's when I first start it up. After a minute or so, it was fine, altho during that minute my A/C compressor kept clicking on and off. I think high flow air filters is the culprit for some of us.

Jeff