I have an ambient temp switch connected to the vac port on my throttle emissions control solenoid for my 2150 carburetor. It's a 78 F-150 with a 5.0L 302, automatic 2WD. Would a bad ambient temp switch screw up my idle? I've disconnected the vac hose and it won't idle at all, and it does the same thing when I disconnect the two wires from the ambient temp switch. If I leave everything alone, I can get the idle down to around 1800rpm, but any lower than that and it stalls.

Is it possible to swap out this throttle emissions control solenoid with another type? I've looked everywhere and can't find an exact replacement, and I have no instructions on how to tune it.

 

I'm not familiar with a throttle emissions solenoid. Are you sure it's not an idle stop solenoid with a dashpot? Can you describe what all connects to it and maybe what it looks like? What does this switch do? Does it raise\lower idle based on ambient temperature?

When you disconnect the vacuum hose and it has trouble idling - are you capping the open vacuum source? If not, that's why it won't idle.

Not being able to idle below 1800 is way out of the ball park; that's not even idle at all. That indicates a vacuum leak, stuck EGR valve, or the idle mixture screws out of tune. Regardless of any sort of emissions control solenoid, you should still be able to get your carb to idle close to the ballpark even if the ambient switch doesn't work. The solenoid isn't going to make a day\night difference.

 

fmc400, thanks for the response. I agree that it's probably a vac leak somewhere, but I've been unable to find it.

Here is a pic of the solenoid

I asked what people thought this was called a few months ago and I got a few different answers as to the actual nomenclature (including idle stop) but the haynes manual calls it a throttle emissions control solenoid. It has one vacuum line going to the ambient temp switch,( and the typical electrical connection coming off the back.

I did cap the vac source (ambient switch) when I disconnected it from the solenoid and I also tried capping the tube coming off the solenoid and neither helped. I'm going to check the vac tube running from the ambient switch to the rear of the engine. Which reminds me, I do not/not have an egr valve and there is nowhere that I can see to connect one on the back of the carburetor.

I would love to just chuck this solenoid and use an idle stop if that were even possible!!!!!

Also, not sure if this helps, but even if it's idling at 1800rmp, if I put it in Drive, it stalls immediately. I don't have a timing light, so going to borrow one tomorrow to see if that might be the problem also.

thanks again for the response fmc400, getting real frustrated here . Off to the garage to hunt and peck some more!!!!

 

ok, did a few vac checks and got 18 across the board, so figure I'm pretty good. Actually spend most of the day cleaning up the garage (and running out to get a last minute mother's day gift). But...my wife did come home from Sears with among other things, a brand new timing light!!! So instead of waiting for tomorrow, I hooked it up real quick before I quit for the day and I'm kinda confused about the results.

I know I'm supposed to have the engine warmed up, but since the idle won't go below 1800rpm, didn't figure it mattered anyway. So I checked it and it said.......it was advanced 30 degrees?? Now how the h-- can it run when it's advanced that far?? Is it possible to dial it back to 6 from that far ahead? I'm about to do some searching on this, but while confirming that I had all the plugs connected properly, I noticed that I'd left the vacuum advance on the distributor capped when I used the timing light. Could that have messed it up? I'll do the timing properly tomorrow after work, but wanted to see if anyone had any thoughts on this. thanks!!

 

To set the base timing, you want to have the vacuum advance unplugged and the line capped off. You also want the idle to be around your idle speed as well, because even though you have the advance capped off, the centrifugal weights in the distributor will still advance the timing at such a high RPM.