Multitude of issues when warmed up

[SBR]

So, let's begin:

1993 Mazda MX3 GS, 235k. No check engine light/codes.
When it warms up fully after about 5-6 minutes, then the issues begin. It goes like this: cold, good warm, then bad warm (where the issues begin).

-Below 2000RPM, the car bucks and lacks power. It won't accelerate smoothly. Any gear, this will happen.
-Idle is erratic. Typically will idle around 1000RPM. If in gear but with the clutch in, idle will increase to 1500RPM. If brake is held down, the engine will go down to 600RPM then back up. The engine sounds like it misfires if it idles in gear.

Maintenance that has been most recently done (ie. within the past 3 months):
-spark plugs (NGK Iridium IX)
-spark plug wires
-distributor (OEM new)
-air filter (FRAM)
-oil and filter (obviously, once a month)
-transmission fluid (GM Synchromesh Friction Modified)
-fuel filter

Some insight and ideas would be helpful.

[wytbishop]

There are two common causes of this issue. First is unmetered air entering through a hole or leak in the air intake system. Inspect the intake piping and all the vaccuum hoses.

Second, and I think probably at least part of your problem is the coolant. The throttle body uses coolant to sense the temperature of the engine to set the idle in cold weather. As the coolant temp increases the throttle body gradually lowers the idle. If the coolant level is low, flow through the TB is intermittent or non-existant. Make sure that the coolant level is right up and that there are no bubbles or leaks in the cooling system. I'll bet $5 this relieves at least some of your symptoms.

[crazycanadian]

Check coolant levels... Check vacuum leaks... Unplug your IAC motor and see if that makes a difference... Then disconnect the vacuum line to the egr valve... If that still doesn't make a difference.. unbolt the egr valve and slip something between it and the intake manafold to block the egr valve off and see if that makes a difference...

[SBR]

Updates:

-thermostat + coolant replaced
-no vacuum leaks
-adjusted idle to 700RPM, much better now

Still have hesitation between 1000-2000RPM while driving, only when fully warmed.

[crazycanadian]

Sounds like you still have a vacuum leak problem... With out a smoke machine you wouldn't fully be able to tell...

But to cover one easy basic would be to check the TPS..

[MrMazda92]

You could spray wd40 over the various vacuum hoses in the engine bay, listen for a slightly higher idle. Have you checked your accordion tubing(the flexible intake "piping" that goes from the stock airbox to your throttle body) by any chance? Remove it, and flex it both up and down while looking into the larger end. If you can see daylight through cracks... Your car is sucking in unmetered air. Not always as noticeable at high RPM, VERY noticeable at low RPMs.

After that, I would set your TPS to spec! =)

Good luck!

[crazycanadian]

You could spray wd40 over the various vacuum hoses in the engine bay, listen for a slightly higher idle. Have you checked your accordion tubing(the flexible intake "piping" that goes from the stock airbox to your throttle body) by any chance? Remove it, and flex it both up and down while looking into the larger end. If you can see daylight through cracks... Your car is sucking in unmetered air. Not always as noticeable at high RPM, VERY noticeable at low RPMs.

After that, I would set your TPS to spec! =)

Good luck!

I have done this a lot on all different cars... 1) wd40 isn't that great... brake clean works better... 2) 9/10 times a car wont idle up....

The best way is to be tapped into the O2 sensor with a scope, or using live data threw a scan tool at watch for the O2 sensor to either change from lean to rich or fuel control to rich...

[SBR]

Kay, it's NOT a vacuum leak. Using both smoke and propane (the PROPER way, not WD-40 or carb/brake cleaner). And this only occurs when fully warmed up. Dead cold, not a single problem, warming up, not a single problem. Warmed and running for 5-10 minutes, hesitation.

I will be changing out the O2 sensors with some known good working ones to rule out them being defective. Possible that it doesn't heat up to operating temperature or just is plain dead.

[crazycanadian]

Just curious if you have done a compression test on the motor at all?

Have you scopped the TPS?

Also for the hesitation I would think more along the lines of a MAF sensor rather then O2's...

If you have a scope you could check your O2's pretty easy with out replacing them...

[SBR]

Would like to say: FUEL

Throwing in a bit of injector cleaner into the tank, and it started running perfectly. No hesitation at all. Started coming back as I refilled the tank.
Replaced injectors with known good ones, zero problems.

[wytbishop]

I should totally have my injectors cleaned. I bet it would improve how my engine runs too.

[crazycanadian]

Would like to say: FUEL

Throwing in a bit of injector cleaner into the tank, and it started running perfectly. No hesitation at all. Started coming back as I refilled the tank.
Replaced injectors with known good ones, zero problems.

Sounds like its getting more narrowed down....

Filling up at the same place all the time with the same gas?? Or have you tryed different places/different grades...

[SBR]

Would like to say: FUEL

Throwing in a bit of injector cleaner into the tank, and it started running perfectly. No hesitation at all. Started coming back as I refilled the tank.
Replaced injectors with known good ones, zero problems.

Sounds like its getting more narrowed down....

Filling up at the same place all the time with the same gas?? Or have you tryed different places/different grades...

More like solved and dealt with. Fuel injectors replaced, still running good.