Misfiring Cylinder 4 on 2002 Merc Sable

[reedjasonf]

I have a 2002 Merc Sable Lx Premium sedan. It has the 6 Cyl, 24V DOHC engine and ~110,000 miles.

First of all, the OBD codes I get at the auto parts store is P1120, P1121. I replaced the TPS twice which is from code P1120 (Throttle Position Sensor - low input) and still having the same problems.

The car runs a little rough. However, when I sit at a red light or stop sign the RPMs run low and eventually the car will shake and the engine light blinks. The OBD also says it detects a misfire on startup (first 1000 rpm). Also, when I'm idling the headlights and dash lights are more dim. When I give the car some gas the lights get brighter which doesn't seem normal but I don't know if it's related.

I already mentioned that I've replaced the TPS. I've also replaced the spark plugs and wires and a mechanic told me that the fuel rail is getting good pressure. I've had the alternator and battery both tested at the auto parts store and they check out fine. I've also checked the ignition system myself using a voltmeter according to the Haynes manual instructions. Battery voltage is 12.4V off and 14.4V idle.

I've been driving the vehicle but when I know I'll be idling for more than a few seconds I just have to keep the RPMs up so the car won't misfire. The only thing I could think of testing at this point is the coil pack but haven't had a chance yet. Any other suggestions?

[AvalonJohn]

With the lights dimming it almost sounds like relays? If you've checked battery, alternator, ignition coil, etc I'm look on the Ford Windstar Forum. Many Windstars have had this problem. I had it too with my Winnie, can't really remember if I fixed though? No longer have the van.

Good luck,

AJ

[reedjasonf]

AvalonJohn, can you be more specific as to which relay it might be? You mean the relays that are in the fuse box?

Thanks for the info.

[AvalonJohn]

Originally Posted by reedjasonf

AvalonJohn, can you be more specific as to which relay it might be? You mean the relays that are in the fuse box?

Thanks for the info.

Here is the Windstar thread .... 12 Ounce helped me out. Not sure if same cause for Sable? See Link on Windstar fourm.

http://www.automotiveforums.com/vbul...lights+dimming