Intermittent Engine Miss

[taurusmph]

My 2000 Taurus with the 3.0 OHV engine has started missing intermittently. Especially noticeable at idle. Runs fine then every 5 to 10 seconds it feels like a dead misfire then runs fine for another few seconds. Check engine light has not come on. Wondering where i should start looking for the problem? Any help would be appreciated.

[Jeff K]

Likely vacuum leak. Use a scan tool to monitor long term fuel trims for both banks at idle and report back with the results. It often takes a while for the PCM to set missfire codes.

[rickpark]

Not an unmistakable miss, but at idle, it seems to be rough although the rpm is not fluctuating and the car runs fine otherwise.

I had to repair a vacuum leak affecting my manual cooling/heating vent controls and I may have some leaks related to that or to the old, hard vacuum lines in the engine compatment.

[pawpaw]

Had a similar sounding random miss on my then new 99 Ranger. Dealer performed a "wet down" test of each plug, wire & coilpack. Found an external crack in #6 spark plug insulator.

After I thought about it some, I remembered it cutting out bad a couple of times while driving up a slight grade in a frog choking rain storm, that should have been a clue for me about a spark problem.

Anyway if the problem seems worse during humid or wet conditions, or when the engine is under load, maybe consider raising the hood at night & look for arcs & sparks & or do the wet down test of each plug & wire all the way back to the coil, or coilpack, or cop, with a spray bottle of water & look for arcs & sparks, or a sudden rough idle.

More thoughts for consideration, let us know what you find.

[john34683]

I just finished chasing down this exact issue. Mine ended up being a headgasket going bad (which was strane since i had no overheating issues). after i replaced gasket the miss was repaired and all is well again.

[taurusmph]

You know, I dont have a scan tool to monitor the long term fuel trims, whatever the hell that is. I have checked all the vacuum lines for a leak and found nothing. Also have replaced the sparkplugs, wires, coil, and IAC valve. Problem is getting worse, engine missing/stuttering all the time now, surging even stronger now. Wondering if it could be in the Engine Control Module?

[Jeff K]

VERY unlikely it si a PCM problem. Ford PCMs very rarely go bad. Without a scan tool to look at live data from the PCM you are just shooting in the dark as far as diagnosis goes. There are MANY MANY places possible for vac leaks other than vac lines, such as upper/lower intake gaskets, PCV system, etc.

[pawpaw]

Originally Posted by taurusmph

You know, I dont have a scan tool to monitor the long term fuel trims, whatever the hell that is. I have checked all the vacuum lines for a leak and found nothing. Also have replaced the sparkplugs, wires, coil, and IAC valve. Problem is getting worse, engine missing/stuttering all the time now, surging even stronger now. Wondering if it could be in the Engine Control Module?

I too don't think it's likely to be the computer.

Well with all of the electrical parts you've thrown at it, it's time for a fuel pressure test, a computer trouble code scan & maybe a compression check, to see if maybe you have a randomally sticking valve. Do you hear any mechanical tic or click when it goes into one of it's missing fits????

Most autoparts stores will scan the computer for pending codes, if your having problems, but the CEL/SES light isn't on. A trouble code clue or two sure would help the diagnosis.

Don't replace any more parts unless you get a positive trouble shooting result.

More thoughts for consideration, let us know how it goes.

[taurusmph]

Checked the fuel pressure at the port on the fuel rail and it showed 40 psi, Seems good enough for that.

[bighank]

Miss at idle especially with load (AC on). Replaced PCV (what a job). Ignition Coil (had misfire codes on 1 and 3) then finally IAC valve. Think that was it. Expensive ($55) but necessary.