Robert560
Senior Member
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Weird "rough" idle problem after ignition changes.
I'm a bit confused by this one. Hopefully someone out there can offer some advice. When I say "rough" idle, I mean shaky... increased engine shake, but not poor running. Here's the story...
Before:
- Stock coil
- NGK BP6ES plugs with .025" gap
- Bumblebee wires
- Premium rotor
- Stock style distributor cap
Ran OK, idled OK, no major issues. Had a problem with the wire boots breaking during a plug change, plus I wanted better shielding so my garage door opener would work, so I upgraded the system.
After:
- Lucas Sports Coil
- New NGK BP6ES plugs, increased gap to .032", figuring a better mate to the higher coil output
- Cobalt Blue ignition wires
- Replaced rotor again, since I was there
- Updated the distributor cap, since I had push-on plug wires now
- While I was doing all of this, I also installed a new Lockheed style brake servo and new check valve.
After firing the car back up, the idle speed had dropped significantly. I had to adjust the idle screws nearly a full turn, if I remember right, to get the idle back up to where it was (adjusted the fast idle to match).
Now here's the weird part. The car runs fantastic, but at idle it has noticeably more shake than it had before. It really doesn't sound any different though... it just shakes more - like it's idling rougher but not sounding or acting like it's idling rougher. The air-fuel mixture seems fine. I'm not getting any smoke or anything funny. And as I said, it runs beautifully. Off idle I have perfect throttle response.
Another weird thing is that the drop in idle speed from start-to-warm (just after you come off the choke) to fully warmed up is much greater than it was before. There was always some, of course, but now there's noticeably more. And it's even more noticeable when the temperature outside is warmer. It's WAY more than before, and as the idle drops, the engine shake/roughness increases. But none of this seems to have any effect on performance - just idle. I know these things don't idle very smoothly anyway... but the difference is significant from what it was before to what it is now... even though it seems to run better now in all other ways.
I've checked the timing, checked for vacuum leaks (including plugging off the new servo just in case the problem was there somewhere), and recently adjusted the valve lash. The carbs were never touched during this process, nor was the Pertronix ignition module, which I've had in the car for over a year now, long before doing these ignition changes.
Does anyone have any ideas on what could be going on here? I'm at a loss as to what to try next. I'm afraid that when summer gets here, the idle drop will be so extreme that I have a hard time keeping the car running at idle. Was it something I did? Or has something happened elsewhere and it was just coincidence the problem turned up now? Any ideas would be appreciated.
Thanks!
~Bob
I'm a bit confused by this one. Hopefully someone out there can offer some advice. When I say "rough" idle, I mean shaky... increased engine shake, but not poor running. Here's the story...
Before:
- Stock coil
- NGK BP6ES plugs with .025" gap
- Bumblebee wires
- Premium rotor
- Stock style distributor cap
Ran OK, idled OK, no major issues. Had a problem with the wire boots breaking during a plug change, plus I wanted better shielding so my garage door opener would work, so I upgraded the system.
After:
- Lucas Sports Coil
- New NGK BP6ES plugs, increased gap to .032", figuring a better mate to the higher coil output
- Cobalt Blue ignition wires
- Replaced rotor again, since I was there
- Updated the distributor cap, since I had push-on plug wires now
- While I was doing all of this, I also installed a new Lockheed style brake servo and new check valve.
After firing the car back up, the idle speed had dropped significantly. I had to adjust the idle screws nearly a full turn, if I remember right, to get the idle back up to where it was (adjusted the fast idle to match).
Now here's the weird part. The car runs fantastic, but at idle it has noticeably more shake than it had before. It really doesn't sound any different though... it just shakes more - like it's idling rougher but not sounding or acting like it's idling rougher. The air-fuel mixture seems fine. I'm not getting any smoke or anything funny. And as I said, it runs beautifully. Off idle I have perfect throttle response.
Another weird thing is that the drop in idle speed from start-to-warm (just after you come off the choke) to fully warmed up is much greater than it was before. There was always some, of course, but now there's noticeably more. And it's even more noticeable when the temperature outside is warmer. It's WAY more than before, and as the idle drops, the engine shake/roughness increases. But none of this seems to have any effect on performance - just idle. I know these things don't idle very smoothly anyway... but the difference is significant from what it was before to what it is now... even though it seems to run better now in all other ways.
I've checked the timing, checked for vacuum leaks (including plugging off the new servo just in case the problem was there somewhere), and recently adjusted the valve lash. The carbs were never touched during this process, nor was the Pertronix ignition module, which I've had in the car for over a year now, long before doing these ignition changes.
Does anyone have any ideas on what could be going on here? I'm at a loss as to what to try next. I'm afraid that when summer gets here, the idle drop will be so extreme that I have a hard time keeping the car running at idle. Was it something I did? Or has something happened elsewhere and it was just coincidence the problem turned up now? Any ideas would be appreciated.
Thanks!
~Bob