Rough idle

SoCal RV Flyer

SoCal RV Flyer

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SoCal RV Flyer
Lately, my IO-320-D1A has been idling very roughly, and I'm taxiing at least 500 rpm higher than normal to keep the engine running somewhat smoother. Mag check at run-up is fine, with my standard 60-rpm drop (from 1800 rpm) on each side.

I took out the plugs, cleaned and gapped them (although they looked pretty clean already), which resulted in no real improvement. Plugs (Tempest massive electrode) have only about 100 hours on them. Checked the timing too, and it's spot-on.

Could this be the result of an air leak in the induction couplers? Or magneto/spark plug lead degradation? The engine has 430 hrs TTSN, so I'm coming up on the 500-hour inspection/service for the Slick mags. Both the main fuel filter and the screen in the fuel servo are clean.

Any thoughts/comments are appreciated.
 
SoCal RV Flyer said:
Lately, my IO-320-D1A has been idling very roughly, and I'm taxiing at least 500 rpm higher than normal to keep the engine running somewhat smoother. Mag check at run-up is fine, with my standard 60-rpm drop (from 1800 rpm) on each side.

I took out the plugs, cleaned and gapped them (although they looked pretty clean already), which resulted in no real improvement. Plugs (Tempest massive electrode) have only about 100 hours on them. Checked the timing too, and it's spot-on.

Could this be the result of an air leak in the induction couplers? Or magneto/spark plug lead degradation? The engine has 430 hrs TTSN, so I'm coming up on the 500-hour inspection/service for the Slick mags. Both the main fuel filter and the screen in the fuel servo are clean.

Any thoughts/comments are appreciated.
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Could be an induction leak, alright. Could also be a misadjusted or creeping idle mixture needle. Get it warmed up, pull it to idle, and slowly pull the mixture control. You should see an RPM rise of 50 or so. More means it's too rich. Less means it's too lean.

If you have a separate primer, check to see that it's in and locked.

When you go looking for an induction leak, use a mirror and light to check the gasket at the induction elbow to cylinder head joint. I have found them blown out, probably by an afterfire (big bang) caused by someone turning the mags to Off and back on again during the runup. The valve overlap allows some of the pressure spike into the induction system.
 
Is it smoother on initial start up? And does this when engine is warm?
 
I agree with Dan. Check the intakes the way he said but look for blue stains which indicate fuel leaks. Sometimes you’ll actually find raw fuel seeping out right after shutdown. Those gaskets only last about 500 hours. If you end up changing them go ahead and change out the lower hoses also. Be sure to clean the intake port really well where the gasket makes contact. Use a scotch brite pad to polish it out shinny clean. It’ll help the new gasket seal better. I like to use a product called fuel lube on the gaskets. It does a great job of sealing the gasket and it’s sticky enough to hold the gasket in place while you get everything lined up.
 
Thanks guys. Great suggestions all around.

Dan, will try the idle mixture test. No separate primer fitted.

NordicDave, yes, I have a monitor. On the last flight after takeoff, EGTs seemed higher across all cylinders by 30 degrees F or so. CHTs were normal.

MooneyDriver78, idle may be a little better when cold....hard to tell.

I have had a couple of backfires when starting, so maybe it is a gasket issue. Visually, they appear to be fine but maybe gasket is blown out on the back side. I've also been meaning to replace the rubber tubing on the oil return lines (just an occasional drip) so this is my big chance!
 
Jdm said:
...Be sure to clean the intake port really well where the gasket makes contact. Use a scotch brite pad to polish it out shinny clean. It’ll help the new gasket seal better. I like to use a product called fuel lube on the gaskets. It does a great job of sealing the gasket and it’s sticky enough to hold the gasket in place while you get everything lined up.
Click to expand...

If helpful... Fuel Lube is marketed as EZ Turn https://www.aircraftspruce.com/cata...MI6cGc__eV6wIVCj6tBh0Pjg8lEAQYASABEgKlJfD_BwE
 
Thanks again. I'll order the parts today and do the install next weekend. I haven't tried Fuel Lube before, but I'll give it a try.
 
Fuel Lube might not be the best stuff here. It's a grease, and those gaskets are under considerable suction at idle, especially during a glide when the prop is driving the engine. The gaskets could get sucked inward. I prefer Permatex Hi-Tack, and apply it only on one side of the gasket so disassembly is easier next time.

Fuel Lube is great stuff in other places, though. You can stick a nut to the end of a long flat screwdriver so you can hold the nut against an inaccessible stud while you turn it with another long screwdriver. Or stick something to your finger to get it into place.
 
Thanks Dan. Parts ordered, and I'll report back with the results in a week or so.
 
Racerx said:
Is it just rough or is it surging?
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It's rough...just requires more rpm than usual to stay lit. A lightweight composite prop doesn't help in the quest for a lower idle speed!
 
Just to follow up:

It runs great! Replaced all rubber couplings and intake gaskets.

It looks like the coupling was leaking on #4 and the intake gasket looked suspicious on #2. Idle mixture was also too lean...took about six clicks on the star wheel to get it right. I guess the degrading idle kinda snuck up on me over time. On the test hop, EGTs were down where they usually are.

Thanks again for the advice.
 
Dan Thomas said:
I prefer Permatex Hi-Tack, and apply it only on one side of the gasket so disassembly is easier next time.
Click to expand...

Probably a DUH question, but I'm assuming this is the engine side, not the intake tube side, correct?
And would there be any reason not to put a very thin film on the intake tube side?
 
Skyrys62 said:
Probably a DUH question, but I'm assuming this is the engine side, not the intake tube side, correct?
And would there be any reason not to put a very thin film on the intake tube side?
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I wouldn't stick Hi-Tack on the engine side. Too hard to clean the gasket off next time. Heat will cook that stuff on there real hard. I didn't use gasket sealants on intake gaskets, but if I did it would be just on the intake tube itself.
 
IO- engine ?
rough idle?
clean the injectors.
 
You actually don’t have to put anything on the gasket for it to seal properly. Fuel Lube/EZ Turn on both sides is what most the A&Ps at my field use, including myself. It’s tacky and can be helpful holding the gasket in place while you line things up.
 
Jdm said:
You actually don’t have to put anything on the gasket for it to seal properly. Fuel Lube/EZ Turn on both sides is what most the A&Ps at my field use, including myself. It’s tacky and can be helpful holding the gasket in place while you line things up.
Click to expand...
Try this, use contact glue on one side only, the side that is easiest to clean. when you need to remove it use Acetone.
 
Jdm said:
You actually don’t have to put anything on the gasket for it to seal properly. Fuel Lube/EZ Turn on both sides is what most the A&Ps at my field use, including myself. It’s tacky and can be helpful holding the gasket in place while you line things up.
Click to expand...
See post #9.
 
A Special Tool that I have developed a fondness for is a

“ Leaf Blower”.

With it ( or press side of clean shop vac) you can pressurize

the Intake or exhaust system with minimal disassembly.

For Ex you slip over stack , turn ON and squirt soaps water.

Intake requires pulling Carb Heat Duct to connect.

carb Heat ON and squirt.

Youhave a fairly high volume of air so air tight sealing not

needed.
 
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