Steeev

Cars a '00 si, only has intake, header, and exaust changed on the car. Was driving to work, and about 5 minutes into the trip, the car started to run really sluggish, but ONLY in the lower RPMs (1k-3kish). Once you past around ~3k, the car picked up and ran smoothly. Occured in all gears, except reverse. Check engine light did not come on until about 10 or so minutes of driving in this condition.

Again, when the car is running(1-3k RPMs) its bogging down/running sluggish, until the car picks up and runs fine. Idle is normal, no stuttering or anything.

Any ideas?

rowe4166

Any check engine lights. Sounds like your car is in limp mode.

ILLEGAL

pull the plugs yet?

markj

my car did the same thing, the timing belt was off a tooth, also had a problem with aftermarket intake doin that also! weird shit

jdm90brx

its the o2 sensor

Fabrik8

Throttle position sensor can do that also, as can the MAP sensor. It's a problem with the ECU seeing a signal that is not right for that operating condition, and using it anyway. So the ECU is adjusting ignition timing or fueling based on inaccurate sensor readings. It can clear up at a certain load/RPM point because at that point the sensor readings are close to what they actually should be. The fact that it does it after driving for a few minutes doesn't necessarily mean much, because the ECU starts adjusting all sorts of parameters after the engine warms up. It does tell you that it's most likely a sensor problem though, instead of something like a mechanical timing problem.

So check the MAP and TPS first, because they're relatively simple to test with just a basic multimeter. If you're fancy you can also use a OBD2 scan tool and see if you're getting any strange readings after the engine is warm, or over a certain RPM range, etc.

Check the O2 sensor also though, because the other sensors (MAP, TPS, etc) tend to cause problems over the whole temperature range that the ECU uses those sensors for. O2 sensors are used or not used depending on open loop or closed loop operation which changes with engine load, RPM, temperature, etc.

O2 sensors are evil, let me say that much. They're one of the only sensors that can partially fail or fail inconsistently or fail over a certain measurement range only. Evil.

Steeev

Thanks to all that commented. This did occur once, and as Fabrik8 said, the last time this happened it was due to a faulty MAP sensor. I unfortunately don't have the tools/parts/know-how to check all of this myself, just needing a few ideas when I go take it in as to what it is. Again, thanks for the responses. I'll be sure to reply again if I take it in and I get some 'off the wall' problem thrown at me by the local mechanic

b-ryan

I had the same problem with my 99 si, I replaced the o2 sensors but it still occured. i finally figured out that the idle air control valve went bad.