High idle when warm?
#1
#2
RF Veteran
iTrader: (1)
With IAC Valve unplug RPMs should drop below "normal", to 500rpms, so barely running, or engine should stall, but its shouldn't "idle normal"
With cold start, idle should be 1,100-1,200rpms
Then slowly drop as engine warms up over next 5 minutes
This is Choke Mode
650rpms warm idle for manual trans
750rpms for automatics
Because the idle RPMs do change when unplugging the IAC valve that usually means it is working, not stuck
Could be ECT(engine coolant temp) sensor is showing engine is over heating, that can cause high idle for better cooling, but long shot
Vacuum leak............MAYBE(big maybe), but that should effect all engine temp idles, and computer should close IAC valve if RPMs are higher than they should be, so unplugging IAC wouldn't change RPMs
Unplug TPS(throttle sensor) see if that matters, also see if CEL(check engine light) comes on, it should, its a sanity test of computer, no CEL means computer is not monitoring that sensor and it should, turn off engine and plug TPS back in, restart and CEL should go off
Unplug MAF sensor as well, again should get CEL should come on, and then go off after its plugged back in
It reads like it could be a computer issue
I had to replace the 3 capacitors in my 1994 Computer last June, because of odd running issues
The 3 blue capacitors seen here: Ford EEC-IV
Under $5 for parts, if you can solder you can do it, or any electronics repair shop can, i.e. TV and Radio repair
With cold start, idle should be 1,100-1,200rpms
Then slowly drop as engine warms up over next 5 minutes
This is Choke Mode
650rpms warm idle for manual trans
750rpms for automatics
Because the idle RPMs do change when unplugging the IAC valve that usually means it is working, not stuck
Could be ECT(engine coolant temp) sensor is showing engine is over heating, that can cause high idle for better cooling, but long shot
Vacuum leak............MAYBE(big maybe), but that should effect all engine temp idles, and computer should close IAC valve if RPMs are higher than they should be, so unplugging IAC wouldn't change RPMs
Unplug TPS(throttle sensor) see if that matters, also see if CEL(check engine light) comes on, it should, its a sanity test of computer, no CEL means computer is not monitoring that sensor and it should, turn off engine and plug TPS back in, restart and CEL should go off
Unplug MAF sensor as well, again should get CEL should come on, and then go off after its plugged back in
It reads like it could be a computer issue
I had to replace the 3 capacitors in my 1994 Computer last June, because of odd running issues
The 3 blue capacitors seen here: Ford EEC-IV
Under $5 for parts, if you can solder you can do it, or any electronics repair shop can, i.e. TV and Radio repair
Thread
Thread Starter
Forum
Replies
Last Post
Rolo75
4.0L OHV & SOHC V6 Tech
6
10-03-2017 06:39 PM