mazdaracer_04

I just got this car and it will start up but it wont stay running. If i give it gas then it will run but if i take it up to any rpms then drop them it back fires everytime. but it wont idle at all. Im thinking its somthimg to do with the air to feul ratio so I was going to try cleaning out the throtle body and the maf with the battery disconected to maybe reset the ratio but if any one has anything else then it would greatly be appreciated. thanks

Baldy

Sounds like classic symptoms of a vacuum leak. Start at the air flow meter (just after the filter), and follow the path of the air all the way back to the engine, checking for leaks at every junction.

confab

This is an old post, and I'm sure it was already solved, but perhaps it would be a good reference. Timing is also something to check. I had similar issues when my crank sensor was off a huge amount.

PistonExGirlfriend

I had the same problem, but if you were to look at my injectors once we pulled them; you'd see why it wouldn't idle.

FCme

I have the same problem It wont stay running at idle untill it's warm and even then it drops untill it almost cuts out and then revs up and idle's rough for a period and drops and almost cuts out and revs back up again I've already checked for leaks and checked the TPS and various sensors but with no joy

Is these a way to pressurise the system when not running to check for leaks ???

thatpoorguy

Definitely sounds like vacuum leak. At idle is the only time your engine develops vacuum due to the suction of the engine while the butterfly is closed. When you have a vacuum leak (a way for air to enter the engine AFTER the maf sensor) the computer only reads how much air is passing by the maf (mass air flow sensor) so any other air entering the engine through a vacuum leak isn't measured by the computer. In a vehicle with a stock Ecu with adaptive learning will throw codes for running lean and probably for misfiring, and will try to add more fuel to compensate solely off of what the o2 sensors are telling it. Since the o2 sensors are telling the engine how to correct from the exhaust side, the corrections come in later than needed so your car will still idle like crap. On vehicles with aftermarket ecu's, the fuel map is set when tuned and doesn't adapt for anything like that, so the engine runs very lean at idle causing detonations, low idle, or it won't even stay running.



Now, thing that can cause the lean condition. Old, cracked, loose, or otherwise not sealed vacuum lines. Intake manifold gaskets, leaking air solenoids, or even a leak in the exhaust prior to the o2 sensor.