Idle Question....strange behavior

A

Athos

Member
Hey All

I have been through this before and it was the Vanos Solenoids. I checked for error codes and sure enough it dinged the solenoids (I changed them quite a while ago), so I replaced both of them and cleared the codes. The erratic idle has improved but is still there, although improved. No error codes this time. Now when the idle dip happens it is very quick, and sharp-it makes the car feel like it is bucking (if that makes any sense) Now it could be a bad solenoid but wouldn't that throw an error code?

I am now thinking maybe MAF? Vacuum leak?

Any ideas or testing suggestions to help diagnose?

Thanks
 
I would check for air leaks - mine ran rough at ilel and it was just the oil filler cap not seated correctly - nothing regarding codes for that.
 
Air leaks across the vaccum system from Maf to exhaust are a possible cause for bad idle, these engines require a completly sealed vaccum system to run correctly. Air leaks will also mess up your fuel trims fooling the car into thinking its running lean due to the unmetered air that has not been measured by the Maf being picked up by the exhaust lambda sensors. To correct what it thinks is a lean condition it will demand more fuel to be injected to richen the mixture, it will add up to 20% more fuel before it gives up and sets the EML to draw attention to to the fault and sets codes for the fuel trims. If you can't find any air leaks its best to do a smoke test by pumping smoke into the intake after the Maf and with the throttle open, throttle pedal depressed to aid the passage of smoke. Once the smoke is being pumped in look for any signs of smoke leaking from all the rubber and plastic vaccum pipes across the engine. Also pay particular attention to the cam cover especially if its the plastic type. I have seen one car that had a leak from the cam cover down the No4 Plug well, close examination found that the cover material was degrading and had started crumbling, hence the air leak, the plug well did however remain oil free. A used replacement was sourced which fixed the leak and put the fuel trims back in spec.
I did build my own smoke tester after looking at Youtube videos and soucing the parts from ebay, a large empty paint can some airline fittings, plastic tubing and some resistance wire and a lamp wick. I use Baby oil to produce the smoke that the resistance wire heats up the oil soaked wick when its connected to 12v battery votage. I either use my compressor to pump the smoke or a bycycle pump which produces enough pressure to push the smoke into the system.
https://www.youtube.com/watch?v=g5W9v0qUF2s

Also woth cleaning the idle air control with carb cleaner to ensure its not gunked up and sticking.
 
Intake hose has a habit of cracking so I hear from the specialist.... Mine went, probably because of the weather/temp change being old plastic, that eventually cracked it, but I also got odd hard to start in the mornings then wild lumpiness until the intake hose had warmed/sealed back with the heat. Might not be the same but worth a look, cheap as chips to replace and 10 min job so might be worth doing anyway
 
Thanks ZOID!

Mine is behaving in the opposite way, when the car is cold it idles fine, it is only after it is warm that it starts dipping, correcting itself, and dipping again.
 
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