I am having a problem with my idle when the engine temps are high (starting after heat soak) and sometimes when sitting still for 2-3 minutes after I've been driving. The idle starts to drop down to 500, sometimes it stalls and sometimes it catches itself and revs back up. It seems like once the car gets a chance to cool off and have some air go through the radiator (I've upgraded to a Fluidyn) everything is ok. I also notice a faint gas smell in the cockpit sometimes when the motor is hot and I'm sitting still at idle, but there are no fuel leaks (it holds 35psi for over an hour).

Usually when I start after heat soak I have to put the gas down all the way and crank a little bit, then crank normally to get it to start (no smoke out of the tail pipe).

Today while the car was idling I jumped the TEN and GND terminals to see if there would be a change in idle (I read somewhere on here, that doing so stops the IAC from working) - the result was no change at all. I took the paperclip out and there was still no change. Idle was steady at 800, pulling -14 vacuum.

Any ideas what could be causing my idle problems? (I've replaced the following parts) fuel pump, fuel pressure regulator, fuel injectors, ignition coils, ecu, plugs, plug wires, vacuum hoses, coolant temp sensor).

Thanks in advance,
-Charlie

 

Jumping the pins together flashes your CEL to give you a code for what is broken. Won't work with a fully programable aftermarket ECU.

 

a good compression motor will pull between 16-18 inches of vacuum at idle. So it sounds like your motor may be a little warm. However, assuming that you aren't loosing much compression after heat soak, i would suggest trying to load the motor down as much as possible at idle to check the IAC.

turn on the A/C, blare the radio, turn on the headlights, the blower motor, and turn the steering wheel. If your car stalls during this process, it usually indicates a faulty IAC. Now, you can adjust the idle manually on the throttle body. If you look where the throotle cable hooks onto the throttle plates, you will see an 8mm nut with a flathead screw in it next to the bolt for the vacuum canister. With the motor at normal operating temperature, break that nut loose, then rotate the screw clockwise to adjust idle, then tighen the nut.

As rajeevx7 said, jumping the ten and ground with the ignition off, then turning the ignition on, will flash your check engine light for any codes in your ECU.

 

Oh yeah, and just as a friendly reminder, third gens are well known for their pulsation dampener leaking underneath the plenum. If you are smelling fuel, that is the first place i would start looking for a leak. I would also suggest replacing it if you have never done that before. And remember, the fuel pressure gauge will tell you that it is holding pressure through the lines and rails until the pressure regulator, but theoredically, if you disconnected the return line and let it pour all over your motor, it will still hold pressure in the lines.

 

Thanks for the ideas guys. I performed the "everything on" load test and the motor didn't stall - just increased rpms slightly.

You make an excellent point about the fuel pressure test, but I forgot to mention that I've had the UIM off and visually inspected the lines with pressure (both before and after the regulator) - there are no leaks in the engine compartment.

The engine may end up being the problem. I have performed a compression test using a piston tester (with valve removed). From what I've read, the readings are not accurate and shouldn't be taken too seriously - but every face of every rotor (front and back) was even. So, I take that as a good sign. If I don't figure this out by next weekend, I'll probably take it to Mazda and pay the $80 to have them do a real compression test. In the meantime - any suggestions would be greatly appreciated.

By the way, I have been getting code 16 since I bought the car (egr sensor) - does anyone think that if the egr valve is stuck open it could cause these symptoms? I know in the manual it says that it can cause rough idle and stalling - but I don't know why it would run fine sometimes and rough other times if the valve is stuck open. I've searched all over the forums and haven't been able to find any instances of people having these types of problems as a result of the egr valve. I plan on taking it off soon to see.

Thanks again,
-Charlie