Idle issue intermittent on lh 1995 129

[Yorkabenz77]

Recently acquired another 95 sl500 with low miles and good records.
Shortly after purchase, it developed a miss shortly after startup after sitting for a week....and after driving and getting up to temp, idle in gear gets bad. Really felt like a typical cap issue with moisture buildup.
After driving for a bit, the engine runs great. Even when it was idling poorly, acceleration was fine.
No fault codes found.
Plugs were iridiums.switched to f8dc4 and gapped.
Ruled out caps, rotors, rear cap covers, and leads.
Upper harness is updated but throttle body is original but shows no issue.
Maf was rebuilt but have ruled that out.
Took out EGR and appears to be moving freely.

If I drive it for a day, park overnight and drive it the next, car doesn't repeat issues. Only seems to be if it sits for multiple days. I will also drive to a destination while it's missing at idle, park.it for a bit and will then give no.issue for rest of day.

Again, it feels like a typical cap moisture symptom or a stuck EGR sucking in unmetered air.

Has anyone experienced this?

I have also noticed the rpm at idle sometimes will sit at 500 rpm and not increase after shifting to p/n. Again, no code...assuming it's a safety switch intermittent issue. It'll do this with a smoothed out idle as well.
Assuming it's not correlated.

Thanks!

 

[Yorkabenz77]

I'd like to add that cap/rotor issue was ruled out buy swapping components from my other m119 that runs completely fine

 

[gsxr]

This is a textbook case of moisture in the distributor caps after a cold start. Adding extra vent slots to the caps will almost always cure the issue. You also must eliminate oil leaks from the intake cam solenoids. Additionally, remove the rotor bracket and inspect the back side of the insulator. Make sure there isn't goop/liquid on the back side of the plastic (it isn't moisture, the liquid does never evaporates).

Swapping caps/rotors from another car doesn't help with diagnosis, the car will run perfectly with either set of caps/rotors. The issue usually only returns when the car is parked for days or weeks, then the cycle repeats.

Full details are in the thread linked below:

FYI Thread 'Essential M119 Ignition "Tune Up" mods [Distributor cap vent / slot]'

Jul 18, 2021

Moderator edit: In addition to cutting extra vent slots to reduce/eliminate condensation inside the caps causing misfiring, oil leaks must also be completely eliminated from the cam solenoid and exhaust cam seals. If there's the slightest trace of oil at the lower edge of the cap, this misfire issue can still pop up occasionally, even with the slotted caps. Read this entire thread. A related "How-To" thread is located here that is also required reading....

• JC220
• Replies: 58
• Forum: M119 Engine

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• 
• 

Welcome to the forum!

 

[Yorkabenz77]

This is a textbook case of moisture in the distributor caps after a cold start. Adding extra vent slots to the caps will almost always cure the issue. You also must eliminate oil leaks from the intake cam solenoids. Additionally, remove the rotor bracket and inspect the back side of the insulator. Make sure there isn't goop/liquid on the back side of the plastic (it isn't moisture, the liquid does never evaporates).

Swapping caps/rotors from another car doesn't help with diagnosis, the car will run perfectly with either set of caps/rotors. The issue usually only returns when the car is parked for days or weeks, then the cycle repeats.

Full details are in the thread linked below:

FYI Thread 'Essential M119 Ignition "Tune Up" mods [Distributor cap vent / slot]'

Jul 18, 2021

Moderator edit: In addition to cutting extra vent slots to reduce/eliminate condensation inside the caps causing misfiring, oil leaks must also be completely eliminated from the cam solenoid and exhaust cam seals. If there's the slightest trace of oil at the lower edge of the cap, this misfire issue can still pop up occasionally, even with the slotted caps. Read this entire thread. A related "How-To" thread is located here that is also required reading....

• JC220
• Replies: 58
• Forum: M119 Engine

• 
• 
• 

Welcome to the forum!

I've ruled that out completely with swapping dizzy caps, and rear cups from my other sl that's been a daily with no issues for years. Has beru caps. The ones on the new car were almost new Bosch which were placed in the old one with no issue. The rotors are also like new.

I guess in a way the rotors could have micro cracks in it but you'd think symptoms wouldn't just go away especially when hot...

No oil leaks

 

[Yorkabenz77]

This is a textbook case of moisture in the distributor caps after a cold start. Adding extra vent slots to the caps will almost always cure the issue. You also must eliminate oil leaks from the intake cam solenoids. Additionally, remove the rotor bracket and inspect the back side of the insulator. Make sure there isn't goop/liquid on the back side of the plastic (it isn't moisture, the liquid does never evaporates).

Swapping caps/rotors from another car doesn't help with diagnosis, the car will run perfectly with either set of caps/rotors. The issue usually only returns when the car is parked for days or weeks, then the cycle repeats.

Full details are in the thread linked below:

FYI Thread 'Essential M119 Ignition "Tune Up" mods [Distributor cap vent / slot]'

Jul 18, 2021

Moderator edit: In addition to cutting extra vent slots to reduce/eliminate condensation inside the caps causing misfiring, oil leaks must also be completely eliminated from the cam solenoid and exhaust cam seals. If there's the slightest trace of oil at the lower edge of the cap, this misfire issue can still pop up occasionally, even with the slotted caps. Read this entire thread. A related "How-To" thread is located here that is also required reading....

• JC220
• Replies: 58
• Forum: M119 Engine

• 
• 
• 

Welcome to the forum!

It's really weird because the symptoms really do seem like it would be a moisture issue...
The intake cam solenoids are seeping oil a tad but internally behind the caps are bone dry and clean...

 

[Yorkabenz77]

This is a textbook case of moisture in the distributor caps after a cold start. Adding extra vent slots to the caps will almost always cure the issue. You also must eliminate oil leaks from the intake cam solenoids. Additionally, remove the rotor bracket and inspect the back side of the insulator. Make sure there isn't goop/liquid on the back side of the plastic (it isn't moisture, the liquid does never evaporates).

Swapping caps/rotors from another car doesn't help with diagnosis, the car will run perfectly with either set of caps/rotors. The issue usually only returns when the car is parked for days or weeks, then the cycle repeats.

Full details are in the thread linked below:

FYI Thread 'Essential M119 Ignition "Tune Up" mods [Distributor cap vent / slot]'

Jul 18, 2021

Moderator edit: In addition to cutting extra vent slots to reduce/eliminate condensation inside the caps causing misfiring, oil leaks must also be completely eliminated from the cam solenoid and exhaust cam seals. If there's the slightest trace of oil at the lower edge of the cap, this misfire issue can still pop up occasionally, even with the slotted caps. Read this entire thread. A related "How-To" thread is located here that is also required reading....

• JC220
• Replies: 58
• Forum: M119 Engine

• 
• 
• 

Welcome to the forum!

Sorry, I misread....
I was assuming you were talking about oil leaks from the exhaust cam seal....
I wouldn't think the solenoids would cause it. They were seeping but it was pretty minimal...and the car has about 63k miles on it.

Damn....if that's it, I'm going to be mad,.lol

 

[gsxr]

The tiny oil leak from the cam solenoids deposits engine oil at the lower edge of the cap, where the high voltage arcs may react with the oil... at least, that's my theory. This is the secondary issue though. Sounds like your cam seals are dry, which is good, those are a nuisance to replace if leaking.

The main problem is moisture. Try cutting the extra vent slots into a set of caps as shown in the thread above. I think there's a >95% probability that will cure your issue. This has worked for dozens of forum members with the identical symptoms you describe.

 

[Yorkabenz77]

The beru caps...which seem to be made with different materials...have never given me issue even with sitting after heavy Florida rainstorms and humidity. This issue was happening in a more dry climate in the Midwest late summer/fall with more dry conditions. Shifting parts and making sure they were dry didnt make a difference and there was no oil within the area

 

[gsxr]

One way to confirm 100% if it's secondary ignition is to view live data from the EZL while the problem is occurring. If certain cylinder voltages spike from ~35 to ~70 while the misfire occurs, it's absolutely secondary ignition. This will show you which specific cylinders to investigate. >90% of the time you'll find the affected cylinders are all on the same distributor cap, usually the passenger side. You'll need SDS with functioning HHT-Win for this, video below at 0:40.

I'd still cut the extra vent slots. It's free, easy, and you have nothing to lose.

 

[Yorkabenz77]

One way to confirm 100% if it's secondary ignition is to view live data from the EZL while the problem is occurring. If certain cylinder voltages spike from ~35 to ~70 while the misfire occurs, it's absolutely secondary ignition. This will show you which specific cylinders to investigate. >90% of the time you'll find the affected cylinders are all on the same distributor cap, usually the passenger side. You'll need SDS with functioning HHT-Win for this, video below at 0:40.

I'd still cut the extra vent slots. It's free, easy, and you have nothing to lose.

Unfortunately, I only have a blink reader and nobody in the area seems to have a proper diagnostic system to get live data