Doesn’t like to run when wet outside

[91merc]

My 85 GM for some reason doesn’t like to stay idling when it’s foggy or rainy outside unless I really give it the beans when I initially start it, you guys have any ideas?

[VicCrownVic]

The Coil is a possibility. Sometimes the housing can get hairline cracks that might even be hard to see but water gets in and the coil goes stupid.
I had this issue on The Ice Car. It wouldn't start on a wet evening after work. Got a ride home, then the next day I went to retrieve it and it started right up since it was dry. The coil looked fine but replacing it solved my issue. May or may not be what you're dealing with, but worth a shot.

Also, shortly before that incident, the car nearly died when I hit a large puddle on the passenger side. Same deal, water hit the coil and it went stupid.

[sly]

CFI has a cold idle pawl for the throttle doesn't it? Works like a carb in that sense. Needs a press of the pedal before starting to remain in high idle initially. At least if everything else is okay... if I remember correctly that is.

[gadget73]

there is a mechanical high idle system, same as a carb uses and it gets gummy sometimes

I was thinking ignition issues though. If its not the coil, how old are your wires?

[91merc]

there is a mechanical high idle system, same as a carb uses and it gets gummy sometimes

I was thinking ignition issues though. If its not the coil, how old are your wires?

my spark plug wires are less than a year old, I broke a vacuum line going to the hockey puck on the drivers side of the throttle body when I was unfreezing my throttle linkage from the negative temperatures we had a couple weeks ago, fixing it yesterday evening seemed to help but it’s not 100%. Doesnt help that it’s been super foggy/ rainy this week either

[kishy]

I haven't touched this thread yet because there's a few places we could go from how it's described in the OP.

Yes, CFI on the 5.0 has a mechanical high-idle mechanism like a carb. And even in moderate weather, basically anything but the hottest of summer days, it does need the throttle cracked open a little bit to start and stay running. Whether that's open enough to set the high idle, or just more open than closed, varies a lot by things like how grumpy your particular car is. But humidity and temperature seem to have a fair bit to do with it.

You refer to 'giving it the beans' when you start it.
With my 85 which has the high idle parts all removed, it absolutely needs throttle to start (even in warm weather) and will stumble and possibly stall if you don't give it a good little rev once it's running. My base idle is also set a little high to discourage the stalling. I know how to make it all work correctly, and it does on my 84, but with the 85, continuing to live with it like this has been easier than taking the throttle body off to drill out the broken screws, so that's why it has persisted like this.

In cool or damp weather, it's even more stumbly and I'm sure it would be stalling if the idle wasn't raised. This has me wondering if your high idle stuff is maybe not working correctly. All of the high idle bits are on the passenger side; the VOTM (vacuum operated throttle modulator) aka dashpot on the driver side is also used to raise the idle but it isn't the primary mechanism for holding the idle high when first starting the engine. That's all done by the spring tension of the choke thermostat (despite there not being a choke), and the pawl and cam on the throttle shaft behind the TPS.

Correct high idle speed for these is ridiculously high, off the top of my head the throttle is supposed to be cracked enough to run it at 1900RPM when fully warm, which sounds like way too much. It's highly likely that many of these cars have had their high idles defeated intentionally by people who didn't realize that the engine racing is actually correct.

[91merc]

I haven't touched this thread yet because there's a few places we could go from how it's described in the OP.

Yes, CFI on the 5.0 has a mechanical high-idle mechanism like a carb. And even in moderate weather, basically anything but the hottest of summer days, it does need the throttle cracked open a little bit to start and stay running. Whether that's open enough to set the high idle, or just more open than closed, varies a lot by things like how grumpy your particular car is. But humidity and temperature seem to have a fair bit to do with it.

You refer to 'giving it the beans' when you start it.
With my 85 which has the high idle parts all removed, it absolutely needs throttle to start (even in warm weather) and will stumble and possibly stall if you don't give it a good little rev once it's running. My base idle is also set a little high to discourage the stalling. I know how to make it all work correctly, and it does on my 84, but with the 85, continuing to live with it like this has been easier than taking the throttle body off to drill out the broken screws, so that's why it has persisted like this.

In cool or damp weather, it's even more stumbly and I'm sure it would be stalling if the idle wasn't raised. This has me wondering if your high idle stuff is maybe not working correctly. All of the high idle bits are on the passenger side; the VOTM (vacuum operated throttle modulator) aka dashpot on the driver side is also used to raise the idle but it isn't the primary mechanism for holding the idle high when first starting the engine. That's all done by the spring tension of the choke thermostat (despite there not being a choke), and the pawl and cam on the throttle shaft behind the TPS.

Correct high idle speed for these is ridiculously high, off the top of my head the throttle is supposed to be cracked enough to run it at 1900RPM when fully warm, which sounds like way too much. It's highly likely that many of these cars have had their high idles defeated intentionally by people who didn't realize that the engine racing is actually correct.

I have noticed that my car seems to either stumble when starting, or it will be in constant high idle so you may be onto something

[DerekTheGreat]

...Correct high idle speed for these is ridiculously high, off the top of my head the throttle is supposed to be cracked enough to run it at 1900RPM when fully warm, which sounds like way too much. It's highly likely that many of these cars have had their high idles defeated intentionally by people who didn't realize that the engine racing is actually correct.

Indeed it is. If I recall right, the number was 2100 RPM on my sticker, just wow. Shifting into gear like that was soul crushing. Also took excessive effort on the brake to keep the damn thing stopped. So yep, I got that as low as I could without it wanting to stall out on my old '85.

[matth825]

Soul crushing doesn't describe it. I can't bring myself to engage a gear until after the high idle drops down on my 85. Car is summer use only so it kicks down fast. I have been tempted to start it in the winter to satisfy my curiosity of how CFI acts in cold weather. The thought of the exhaust riser valve getting stuck shut stops me from doing it however.


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[DerekTheGreat]

The one on my car was nice and free. I think CFI looks better under the hood, but SEFI is the way to go from a practicality standpoint. My '85 felt archaic compared to my '88. Even when it's below 20F, the '88 only idles high for maybe 30 seconds and then it gets down pretty low. My '85 would want to idle for minutes before it would come off high idle without being fussy. I'd recommend swapping to SEFI, but given you only use it in the summer, I don't think I'd bother.

[gadget73]

The idle speed specs for high and low are on the sticker under the hood. I was thinking it was more like 1800, which is not unusual for a carb application. Shouldn't take a stupidly long time to warm up enough to drop the high idle out anyway.

[DerekTheGreat]

Took longer than I wanted it to. Once I fire my engines up, I give them about fifteen seconds of run time before it's clutch in, grab gear, clutch out and go. My slushbox equipped cars get a similar strategy.

[matth825]

When I first got the car I tossed around the idea of SEFI. Biggest reason why I didn't go that route was finding all the parts. Road salt long ago sent a majority of the Panthers in my area to the crusher. Occasionally I find one in a yard but they are a lost cause…typically complete trash with very few useable parts. Didn't want to bother scouring eBay, either.

The CFI has grown on me and I do like the look. It fits the car appropriately. It has proven to be reliable for the most part, thankfully. When it does finally kick the bucket I've got the appropriate 2150 carb on the shelf ready to take over.


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