Quick back story:
I've got an 87 4Runner with 426,000 on it with an engine replacement with a reported 75,000 on it.
Yesterday it was raining with very high humidity, and colder air temps. The engine idle would drop to about 500 rpms and continue to fall. Sometimes it stalled out. I noticed this in the morning.
I had to keep my foot in it to keep it running. When I accelerated it was almost like an old Quadrajet carb with a "bbbbbb-BWWAAAH" like throttle response. Once I had traveled about 10 miles it seemed to clear up.
Later that day, I was poking around the throttle body. It has a dashpot diaphragm underneath the return spring stop. If I inflated the diaphragm it would hold the correct idle.
I did a bunch of short trips shopping and after each stop the crappy idle and unresponsive throttle would come back.
Today, without fixing anything, the idle is normal. The dashpot is collapsed as it was yesterday.
Could the rain just be a coincidence? Would a bad or sticking EGR do this?
weird coincidence, I had a 87 4X4 with a 22r that suffered the same problem.
My motor only had about 30k on a fresh rebuild at the time. It was at night, raining, and very cool when it did the same danged thing. I was on the way to a hospital (girlfriends family member checked in) so I never stopped to troubleshoot, but the next day all was fine.
I then drove the truck 100k miles over the course of 6 years and never had the problem come back... It still wonder what it could have been (seriously).
I bet the throttle body was icing. Make sure the coolant lines to it are connected and not blocked with rust or other mung.
The dashpot is an emissions device. Just keeps it from decelerating quickly. I don't run one at all on my 22RE. It isn't involved in idle at all. When you "pump it up" you're just jamming the throttle body open a little.
It sounds to me like an issue with the idle control valve. There were a couple of versions of this thing- not sure if '87 is like mine or not. Is there a little device screwed to the bottom of the intake with four hoses going to it?
Looks like this:
Yeah, I couldn't remember the name of that. Kind of like the IAC on my Caprice. I've got the bootleg shop manuals for an 88 4Runner, so I'll have to do the diagnostic checklist before I throw parts at it. Mostly consisting of "blow on this. No resistance. Blow on this resistance."
I did use a bunch of carb cleaner in the intake area when I first got the truck in March. Might have soaked it, but I've had no issues until now.
I don't think they fail a lot- might be worth a trip to a junk yard. They're pretty simple devices.
