slarson03

I have a 2002 Ford Taurus SEL with the 3.0L DOHC engine. It has had a rough idle for a few months now.
I have read codes P0316, P0301.
I replaced the spark plugs, the old ones were worn but the new ones didn’t improve the idle problem.
Swapped cylinder 1 and 2 injectors still got P0301.
Next I replaced the coil pack and that fixed the problem for about 3-4 weeks, then the rough idle problem slowly returned, now it’s as bad as it was originally.
The only code since the coil replacement was P0300.
I have noticed that the rough idle stops immediately when the A/C is turned off.
Not sure what to check next, since replacing the coil fixed the problem for a short time that makes me think it’s not a mechanical problem (compression, fuel pressure…).

tbird100636

When you did the Coil Pack or the plugs did you replace the plug wires??? I did plugs on my 2001 Taurus SEL 3.0L Duratec without the wires and got a misfire at idle. After replacing the wires, the misfire was gone. Look at the porcelin insulators where the plug wires attach. If you see black thin burn lines then the plugs were carbon tracked, meaning the plug wires are too, causing a flashover, and hence, a misfire.

__________________
Master ASE Certified L1 Chrysler Technician- still a Ford fan at heart.
1964 Thunderbird Hardtop- Chantily Beige- 390 FE 4V V8-Uncle's Car
1966 Thunderbird Convertible- Red- 390 FE 4V V8- Uncle's other car- waiting for paint and body work!!!
1967 Mustang Convertible- Blue- 289 V8- helping a friend re-assemble this classic

CostlesS

I have a similar problem with Merc. Sable 2002, 24V. Engene running rough with A/C on, only. Cylinder Ballans test shows that, sometimes, cyl.1 have misfire.
I replaced the spark plugs, and sp.plug wires (In cyl.1 - twice). Sp. plugs, and sp.plug wires was fine, and this does not help.
Now, I have two choices. The first is to replace the coil pack. Second - reprogramm computer (PCM).

SHOZ123

Needs the air adders modified. See if the dealer has a reflash upgrade for you or make sure the IAC is working as it should.

Cheap and permanent fix is to open the throttle plate just a hair, disconnect the battery then let the car relearn idle.

To set the throttle stop screw..........

Only make the following adjustment in the event the TRC screw does not contact the throttle lever arm.


1.) PLACE a 0.002 inch feeler gauge between the TRC screw and lever arm. ADJUST TRC screw until it just contacts the feeler gauge.

2.) REMOVE the feeler gauge and turn the screw clockwise a half turn.

This should leave the throttle plate just a hair open which reduces binding and also gives the IAC more headroom.

SHOZ123

The procedure for relearning the idle is ....

On a warm engine, disconnect the battery for a minute. Start the car and let the idle stabilize in park at around 650-750 rpm. The shift to reverse and let the idle stabilize. Then turn on the AC MAX, making sure the temp setting is low enough to kick in the compressor, when still in reverse and let the idle stabilize. Then shift to park with the AC still on and let the idle stabilize.

tbird100636

OK, so how do you know the engine doesn't have a carboned up or burned valves??? I'd make sure the cylinder in question doesn't have excessive leakage during a leakdown test before toying with the throttle body adjustment. If you had a stalling issue and a low idle speed then maybe I'd consider re-adjusting it.

__________________
Master ASE Certified L1 Chrysler Technician- still a Ford fan at heart.
1964 Thunderbird Hardtop- Chantily Beige- 390 FE 4V V8-Uncle's Car
1966 Thunderbird Convertible- Red- 390 FE 4V V8- Uncle's other car- waiting for paint and body work!!!
1967 Mustang Convertible- Blue- 289 V8- helping a friend re-assemble this classic

SHOZ123

Well other than the fact cars today seldom burn up valves I don't know. Just offering suggestions that have worked for me.

I don't see how opening the TP and taking some load off the IAC would hurt anything though.

CostlesS

I have a more complex situation. Engine makes about 1 misfaer (cyl 1, only) every minute if the AC is switched on, transmission shift to reverse or drive, and car is not moving. In any other situation, engine running like new. Cylinder Ballans test-100% in all cylinders. Injectors -pass. Missfire - pass. Long fuel trn. 0%. Short fuel trn. +- 2%.

tbird100636

It doesn't happen allot but I'd say it's a little more than seldom. Just a little carbon build up from short trips and no heavy acceleration or highway driving causes leakage around the valve and eventually burning. I see it every so often on DCX cars. As for costless, is it setting a Check Engine light???

__________________
Master ASE Certified L1 Chrysler Technician- still a Ford fan at heart.
1964 Thunderbird Hardtop- Chantily Beige- 390 FE 4V V8-Uncle's Car
1966 Thunderbird Convertible- Red- 390 FE 4V V8- Uncle's other car- waiting for paint and body work!!!
1967 Mustang Convertible- Blue- 289 V8- helping a friend re-assemble this classic

CostlesS

Thank's SHOZ123 for simple method for setup throttle stop screw. I can change the position of throttle with additional nuts. This will save the original setting. In a situation where we have a DTC P0316 (misfire on startup) and / or P0300 (random misfire), setting the throttle stop screw may help.
The same, only in Russian:) Большое спасибо SHOZ123 за простое объяснение как настроить регулировочный винт дроссельной заслонки. Для эксперимента, я накручу на регулировочный винт дополнительную гайку и с ее помощью изменю положение заслонки. Таким образом мне удастся сохранить начальную настройку регулировочного винта. В ситуации, когда мы имеем коды: P0300 (пропуски зажигания в случайном порядке) и/или P0316 (пропуски зажигания при старте двигателя) - этот метод может помочь. Конечно, при условии, что нет утечек вакуума.