New to me CS rough idle - Solved

[HBP]

Picked up a 2008 CS with 102k on it from a good friend who upgraded to a newer CS.  Car was dealer maintained and ran well for him, but I'm having some problems right off the bat and could use a little help.

 

Wasn't able to drive it for a few months after picking it up, but it was started regularly.  When I finally went to drive it, it wouldn't shift out of park, and after some research, fixed the corroded wires in the drivers foot well and replaced the original battery with a new one.

 

Took it on a 100 mile round trip and it ran great, tanked up that night and parked it.  Next day it idled rough and the check engine light was on.  Installed a new gas cap and pulled each fuel pump fuse separately for the low pressure fuel pumps and ran it, no change in the rough idle.  Picked up the Durametric SW and checked the fuel pressure, consistent at about 40 bar.  

 

There were a number of trouble codes stored in the engine module that were related to the corroded splice issue, along with 3 possibly related to the idle:

1372 Valve lift control, bank 1 implausible signal

1351 Valve lift control, cylinder 1 implausible signal

0303 Cyl 3 misfire detected, value below lower limit value

 

Durametric showed misfire counter for cyl 3 was slowly but consistently increasing at idle, and the ignition counter misfire count was increasing constantly.  Cleared the codes and took the car for a couple of short drives, as well as a number of starts idling in the garage while checking other parameters, couldn't get the codes to reoccur but the misfire was still there.

 

Next changed out the coils and plugs.  Coils were version .02, but had no signs of cracking or arcing, new coils are version .14  Plugs had 17k on them but changed out too.  Started it up, idle still rough and the 1351 and 0303 codes finally reoccurred.  Cyl 3 still increasing in misfire count at idle and the general Ignition counter misfire detection number constantly increasing.

 

I've read about valve actuator issues connected to the 2 lift codes, but the constant misfire on 3 has me wondering if that's the root and it may be from the injector?  Compression test be helpful at this point?  Any suggestions would be appreciated.

Edited January 17, 2017 by HBP

[Fmscell]

Your misfire may be due to carbon build up or a vacuum leak & not actually plug/coil related. Smoke test for vacuum leaks first, make sure the PCV isn't over vacuuming & remove the intake & look at the valves. You may need to walnut blast the carbon off the valves.

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[HBP]

Thanks for the reply, I was thinking the same thing about carbon build up.  Was going to do a compression test earlier today so I loosened the plugs when the engine was cold and tightened them just snug enough, reset the codes, then warmed up the engine.  Much to my surprise in the 10-15 minutes warm up, just a handful of misfires on #3 and the idle sounded and felt significantly better.  

 

So I'm thinking running well initially rules out carbon build up?  Also wondering if it rules out an injector issue?

 

Put the air cleaners back on and took it for a 20 minute ride.  No misfires on #3 at anything other than idle, and even then seemed to be more prevalent with a load in drive than park or neutral.  Still not quite right though as it's inconsistent.  No codes reappeared today.  

 

 

[HBP]

Wanted to follow up on this thread with the final solution.  Did a compression check and the numbers for bank one were all consistently 30-40 psi lower than bank 2.  The misfire problem became much more consistent and the rough idle was the norm.  

 

Ended up replacing the valve lift actuator at the rear of the bank 1 head and that solved the problem.  Zero misfires on bank one now, esp cyl 3, and the smooth idle is back.  Also seems to have better acceleration in the low RPM range.

 

Many thanks to member Oatmeal Adam for his input in troubleshooting the problem!