P0304 Rough Low Idle

[Schlotzky]

Let me first apologize for posting about a common subject but searching has not yielded any results for me.

My brother in law's 2001 Lincoln LS with the 3.9L V8 has a very rough idle. It started as a light occasional miss at idle and has progressed to what feels like a misfire. Above 1100 or so RPM, the engine runs smooth, and the car does not seem to be down on power.

I replaced COP #4 and checked the plug which was replaced ~10k ago. The plug is a nice light brown and is gapped at 1mm. I also checked all injector plugs and re-seated #4. I cleared the code and it came right back after a few minutes with the same rough idle.

Lastly, I swapped COP and plug #1 with #4. No change apparent but I haven't cleared and rechecked the codes for moving miss. What's next?

P.S. Cylinder 4 is the one closest to the firewall on the passenger side, correct?

 

[joegr]

Replace all COPs and plugs. Yes, #4 is passenger side at the firewall.

 

[Schlotzky]

The plugs are about 10k old and are 100k platinum plugs. I cleared the code after swapping the plugs and coils from cylinder 4 and cylinder 1 and the code came back misfire cylinder #4, so it is not following either the plug or the coil.


I appreciate the response, and no offense, but if it's thrown only cylinder 4 misfire 3 times in a row and neither the coil nor plug on cylinder 4 is causing it, wouldn't the chances of it being a different coil or plug be slim to none?

 

[scjmc]

Like joegr said just replace all the COPS. I have had 2 of these cars, and thats the best thing to do. My 06 would throw code for cyl #7 misfire. Replaced #7 coil and then it would give an injector wiring code that would keep coming back. When these coils are failing they cause all sorts of issues. 8 new visteon coils will run you less than $200.

 

[Schlotzky]

Wouldn't a (or several) bad coil(s) cause a miss at any and all RPMs though, if not especially in hard acceleration? This thing runs buttery smooth above 1200 or so RPM and seems to have all of it's original power at WOT.

 

[oddball]

It doesn't have to make sense. Just accept it and move on.

More technically, the COP failures for the LS are of the more marginal kind, so the errors are intermittent and can occur at different areas for each case. It's not a hard failure. That would be too easy.

 

[Schlotzky]

Well it seems to be unanimous so I suppose I can't argue with the Lincoln guys.

Are the Visteon coils advisable? The replacement I put in was a United Ignition Wire coil from rock auto. Maybe I can return it and get the full Visteon 8 set if that's what's recommended. My brother in law just had a kid 3 days ago and is living on one salary between the three of them so I'm trying to keep the budget as tight as reasonably possible.

 

[joegr]

Don't cheap out on replacing the plugs either. Even though they only have 10K miles, a bad/marginal coil will damage a spark plug. A damaged spark plug will then damage a coil, and the cycle repeats.

Marginal coils cause RFI/EMI noise and this can confuse the PCM into giving all sorts of incorrect codes. This is why you need to replace the coils and plugs first. After this, you may still have an issue, but it will be easier to troubleshoot.

 

[jjcool00]

Well it seems to be unanimous so I suppose I can't argue with the Lincoln guys.

Are the Visteon coils advisable? The replacement I put in was a United Ignition Wire coil from rock auto. Maybe I can return it and get the full Visteon 8 set if that's what's recommended. My brother in law just had a kid 3 days ago and is living on one salary between the three of them so I'm trying to keep the budget as tight as reasonably possible.

The visteons are only 179 for all 8 with free shipping. The motorcraft plugs are about 5-6$ each. So all in all youll spend less than 225 if you do it yourself (it's easy to do).

 

[scjmc]

I got Motorcraft plugs and Visteon coils on ebay for a tad over $200.

Yes, the Visteons are advisable. They were the OEM supplier for Motorcraft and are made in Hungary. Lots of us have installed these and had good luck with them. OEM is also advisable, but they are more expensive and now made in China.

 

[Schlotzky]

As an update, I ordered the coils (ACDelco) as I could no longer find the Visteons for whatever reason, and while they were shipping, the car was driven one more time, at which point it died entirely. One of the timing chains snapped. The stupid plastic adjusters shredded to pieces filling up the inside of the cover. We replaced all timing chains and used upgraded parts from an aftermarket company and when we got it back together with the new coils, it was still running rough. I haven't yet heard which cylinder is coding, but we also replaced injector #4 in earlier troubleshooting.

Just over 100k miles and the timing chain breaks? What a horrible engine design. Glad Ford cut ties with Jaguar for reasons like this.

 

[joegr]

...Just over 100k miles and the timing chain breaks? What a horrible engine design. Glad Ford cut ties with Jaguar for reasons like this.

Yes, there were some mistakes made there. The timing chain tensioner issue was corrected by the 2nd gen of the LS. Jaguar went on to greatly improve the timing chain system on the AJ engine. It seems to be a really good and solid design at the moment.

Ford's reasons for selling off Jaguar were financial.

 

[Schlotzky]

We re-seated all the COP connections and it's running smoothly again. Maybe GM did a better job with the COPs and they'll last a while.

Anyway, I think we finally have resolution. Thanks for the help, guys.