Celica Forums General Discussion Engine and Performance 2000 Celica PO300

Hi all,

I'm new here and a fairly new Celica owner. I took a 2000 GT 6 speed in on partial trade, my plan is to fix the car up and try to daily it. Anyways, since purchasing the car the idle and throttle response has never really acted right. I have a scanner tool and I replaced the TPS as it threw the code. This didn't really seem to do anything except the check engine light went off. So, I did some more digging and I read about the IACV and so I took took the throttle body off and cleaned it (the carbon build up was ridiculous) as well as cleaned the IACV and replaced the gasket. I did not remove the black plastic piece on the IACV, only where it mounts to the throttle body and cleaned it. So I finally got all of that put back on tonight. I go to start the car and it is still hard to start and the idle is WAY worst than it was before. I also got the CEL throwing the PO300. The brake pedal is also extremely hard to press in now... Are there any ideas on what to look for? I'm fairly mechanically inclined, I just changed the head gaskets in my wife's 2003 Subaru Legacy about two months ago and I have had zero issues from that job (knock on wood). I would just like some things to try to look out for instead of just throwing parts at it. Thank you for any/all help!

Sebastian Roher

Hard to start and bad idling may be caused by loose, leaky vacuum hoses around the throttle body, or a bad MASS AIRFLOW SENSOR. It could be giving the ECU all wrong air data.

The MAF is a DENSO sensor, trapezoid -shaped piece with a connector, sitting on top of the air duct, between the air filter box and the throttle body.

Check to make sure connector is plugged in securely and all wires and terminals are intact and seated properly.

You can try to clean the sensor element by spraying it with non-residue contact cleaner. Since it's hard to test it electrically, the sure system test is to swap in a known-good MAF sensor from another car. Most Toyota and Lexus engines use the same DENSO MAF sensor.

After cleaning or swapping the MAF sensor, reset the ECU by removing the battery's negative cable and wait 5 minutes for complete data erasure. After this the ECU will work with new MAF data and remap the air/fuel mixture.