intermittent misfire?

[Brian Skinner]

I know this is on my duratec , but it took forever for a responce from taurus forum. Anyhow i get faster responce and youre not nearly as rude. Now for my concern maybe yall can answer since im getting no responce from the other forum. My 03 S code taurus seems to have an intermittent misfire i cant always detect. It seems to happen either when cold or the a/c or defrost on otherwise its a smooth runner but that supposed intermittent misfire is annoying me. I did replace the fuel filter and clean the iac and maf but i'm still puzzled. Forgot to mention it has motorcraft aftermarket wires(no numbers on motorcraft wires like the factory ones would have) Please help

 

[sperold]

A misfire usually gets the CEL to light, and most often flash rather than stay constant. Check your codes (the stored ones otherwise).
If it is a true misfire, the coil is always suspect.

 

[Brian Skinner]

I haven't received any codes by light. I'll have to get a code reader to see if there are any codes. For the most part its a great runner. Another question would be that would ethanol fuel cause this concern. I have used ethanol gas and only the one that says 10% not 20 or 85%. I dont know if that would have any effect. Please help.

 

[SHOdded]

When you say "happen when cold", do you mean weather is cold outside but car is warmed up, or car is not yet warmed up, or ...?

Have you had electrical problems on this Taurus before? Checked the grounds? The ones on the Gen I/II SHO are frequently an issue, so worth checking. When were the plugs last checked/changed?

Do gas stations supply non-ethanol gas in spring/summertime? We are "winter gas" year-round here in MD. May be worth running some Techron in the fuel next time you fill up.

There are also cases of low refrigerant causing the A/C to cycle too often, leading to perceived misfires.

 

[Brian Skinner]

I'm not exactly sure when the plugs and wires were done but i will definitly check those. What i mean is when i turn it on, wait for the seat belt chime to quit chiming then start the car sometime it seems like it hesitates before it goes into open loop then revs up to around 1500 then you have to kick it down loke its carburated to get it to settle down. Thats what i mean when cold. It also happens when the a/c kicks on or so it seems. About the question about ethanol gas we do have station that doesn't have ethanol gas.

 

[Brian Skinner]

Its been driving me nuts please help.

 

[rubydist]

ok, your description does not sound like a misfire at all.

btw, your 03 will be obd2, so you need a code reader to get codes.

when the engine starts, it is automatically in open loop from the moment you turn on the key until the pcm decides to take it into closed loop, either after detecting proper coolant temp for closed loop control, or after the open loop timer expires.

if you start the engine, and it revs up to 1500 and does not want to come down, that is nearly always due to a sticky iac.

when the a/c kicks on, the engine load increases, so the pcm opens the iac slightly to get a little more air going into the engine to keep the rpm constant even with the added load. if the iac is sticky, you can often feel the engine rpm drop when the a/c clutch kicks in. sometimes, you will also feel the rpm kick up a bit when the a/c clutch opens.

the conclusion I draw from all of the above is that your iac is suspected of being sticking. it is possible to clean them, but only very rarely is it successful in resolving the sticking, so the recommendation is to install a new iac.

and also btw, just because you put in a new iac does not mean that it will not be sticky - my experience is about 1 in 5 new ones stick right out of the box.

and you should also be aware that the new iac may need a different duty cycle to keep the engine running at the right speeds, so don't be surprised if you need a couple weeks to go by for the pcm to 'learn' how to operate the new iac, after which it should idle fine.