Uneven Idle 2005. No CEL.

skianian

Member
Hello All!
My wonderful van has recently developed an uneven idle only when warmed up to operating temp. Great power, mpg, starting, etc.... just the pesky idle when warm. Upon start when cold....idle is perfect. Van has 120,000 miles. Anyone experience these symptoms? So far, I've cleaned MAF. Suspecting EGR or fuel pressure regulating valve. No codes.
 

skianian

Member
I believe the answer is yes. I will do the leak test this weekend and see what that tells me. Thanks for the tip!
 

Midwestdrifter

Engineer In Residence
Beware, a leak test will not tell you if an injector is overfueling. The best option is to perform the smooth running test with MB STAR/XENTRY machine. You can also unplug injectors one at a time to see which cylinder has the least affect on the idle. That will at least pinpoint the trouble cylinder(s).
 

Midwestdrifter

Engineer In Residence
Roger that. Could you explain why it runs fine when cold?
Injector malfunctions can be temperature sensitive. When the injector warms up, it starts leaking.

There are other causes though. Mechanical damage to a cylinder for example. Since you have an 05, you won't have air issues which can cause rough idles. Since you have no codes, that typically means injector or cylinder issues. You can try a hail mary and change the fuel filter. You can also try running the van without the MAF connected.
 

skianian

Member
That makes sense. Thanks so much for the intel. I never thought I would say "I hope it's a bad injector" but when compared to a damaged cylinder, I'm happy to buy an injector. Now to find out where I can have a smooth running test completed.
 

veganxxx

Member
Besides an injector I would think a failing fuel quantity valve or rail solenoid could have a similar effect. Tolerances are fine for cold fuel but the thinner it becomes the less pressure control is working. What do others think about that theory?
 

skianian

Member
I performed the "test" of unplugging one injector at a time and it was pretty difficult to identify one culprit. The smooth running test is my next step once I can find someone who can perform it. One more data point though....both when I unplug the MAF and/or EGR (which forces limp home mode correct?) The symptoms become even more evident. Does limp home mode create a richer mixture due to the turbo being taken out of the equation? If that's the case, it would make sense that it makes the surging more evident if that cylinder is seeing an even richer mixture. Fuel filter has 11,000 miles on it...can't imagine it's that unless I picked up some uber terrible fuel at some point.
 

skianian

Member
I'm having a heck of a time finding someone who can perform a smooth running test locally. Plan from here is to run some BG 245 through it and see if I get lucky with that. Will do the smooth running test as well once I can find somewhere to do it.
 

DRTDEVL

Active member
Where are you located? Perhaps a member here can point you in the right direction.
 

owner

Well-known member
Wait you just said "surging". If its it bad enough to cause that it must be a very bad injector (which you should have noticed on the unplug test) or its the rail solenoid. Is there a loud knocking sound or just general unevenness or surging?
 

hkpierce

'02 140 Hi BlueBlk Pass
Besides an injector I would think a failing fuel quantity valve or rail solenoid could have a similar effect. Tolerances are fine for cold fuel but the thinner it becomes the less pressure control is working.
possible, but I would expect a rail pressure code.
While I tend to agree about an injector, when I installed new o-rings on my OM612 fuel quantity valve the engine surge did diminish. No codes at low to medium high rpm and load. I don't know if that rebuild is possible on an OM647, and Skianian has kept that information hidden.
 

skianian

Member
Sorry to leave that out. It's a 647 and therefore I understand the whole rail would need to come out.
While I tend to agree about an injector, when I installed new o-rings on my OM612 fuel quantity valve the engine surge did diminish. No codes at low to medium high rpm and load. I don't know if that rebuild is possible on an OM647, and Skianian has kept that information hidden.
 

skianian

Member
Wait you just said "surging". If its it bad enough to cause that it must be a very bad injector (which you should have noticed on the unplug test) or its the rail solenoid. Is there a loud knocking sound or just general unevenness or surging?
I'm pretty sure surging is the right term. It's very rhythmic rather than random/rough idle which makes me think it's a single cylinder affected rather than the rail pressure... i'm definitely making assumptions though. Regarding the unplug test, the problem injector would be the one that causes the least-noticeable miss, is that right? Lastly, I have zero visible smoke.... wouldn't a very bad injector cause smoke?
 

skianian

Member
Wait you just said "surging". If its it bad enough to cause that it must be a very bad injector (which you should have noticed on the unplug test) or its the rail solenoid. Is there a loud knocking sound or just general unevenness or surging?
No knocking. Runs like a champ other than idling when warm.
 

veganxxx

Member
I’ve had a quantity valve cause a surging idle before without a code or CEL. If the quantity valve or fuel rail solenoid are fully bad they will throw a code that causes limp mode so at least you can rule out a total failure. Just as a refresher, the quantity valve doesn’t come into play for 20 seconds so one test would be-

after engine is warmed up, turn it off and restart it. Does the surging happen right away or does it take 20 seconds to start? That will be your answer on the quantity valve.
 

skianian

Member
I’ve had a quantity valve cause a surging idle before without a code or CEL. If the quantity valve or fuel rail solenoid are fully bad they will throw a code that causes limp mode so at least you can rule out a total failure. Just as a refresher, the quantity valve doesn’t come into play for 20 seconds so one test would be-

after engine is warmed up, turn it off and restart it. Does the surging happen right away or does it take 20 seconds to start? That will be your answer on the quantity valve.
I'll give that a try. Thanks much for the tip!
 

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