4.6l Intermittent High Idle. Why?
#1
07-12-2005, 10:07 PM
4.6l Intermittent High Idle. Why?
Hello:
Working with my 1998 Expedition 4.6l. Occasionally, it will exhibit a high idle up to about 2200 rpm in neutral or about 1200 rpm in drive. Seems to only do this when hot. Has about 107k miles on the clock.
I replaced the IAB and it 'seemed' to fix it. Then about a week later - it's back!
The last time it did this, it threw a CEL, code P0122 "TPS Low error" - or something like that. So I replaced the TPS and it was fine for a couple days then - it's back!
When it does this, it is like the cruise control is on. Of course it is easy to slow down with the brakes, but it is very annoying. Sometimes the idle will ramp up and then settle down. Pressing the throttle to WOT has no effect and I have checked all the linkages while it was exhibiting the high idle problem and none are bound up. also manually rotated the throttle plate to the stop and nothing changed.
I have pinched off the vac hoses that attach to the intake and no luck.
The only thing I can do to let it idle down is to disconnect the ISC (I have also replaced this part too). Sounds like something is commanding a higher idle? Some other sensor?
Anyone had this problem before? Any other suggestions? I am at a total loss.
Best Regards,
Steve
ttlx
Working with my 1998 Expedition 4.6l. Occasionally, it will exhibit a high idle up to about 2200 rpm in neutral or about 1200 rpm in drive. Seems to only do this when hot. Has about 107k miles on the clock.
I replaced the IAB and it 'seemed' to fix it. Then about a week later - it's back!
The last time it did this, it threw a CEL, code P0122 "TPS Low error" - or something like that. So I replaced the TPS and it was fine for a couple days then - it's back!
When it does this, it is like the cruise control is on. Of course it is easy to slow down with the brakes, but it is very annoying. Sometimes the idle will ramp up and then settle down. Pressing the throttle to WOT has no effect and I have checked all the linkages while it was exhibiting the high idle problem and none are bound up. also manually rotated the throttle plate to the stop and nothing changed.
I have pinched off the vac hoses that attach to the intake and no luck.
The only thing I can do to let it idle down is to disconnect the ISC (I have also replaced this part too). Sounds like something is commanding a higher idle? Some other sensor?
Anyone had this problem before? Any other suggestions? I am at a total loss.
Best Regards,
Steve
ttlx
#2
07-12-2005, 10:45 PM
What is the IAB? Did you mean the IAC? If not, then I'd clean that out to see what it's like.
That TPS code was strange though and I'm surprised replacing it didn't fix your problem.
I was having trouble with my truck starting and no one could figure out what was wrong. It was a couple weeks later it finally threw a EGR code and I was able to get it fixed. That's what sucks about these computer controlled vehicles. A Sensor could be starting to go out but you won't know until it completely fails.
That TPS code was strange though and I'm surprised replacing it didn't fix your problem.
I was having trouble with my truck starting and no one could figure out what was wrong. It was a couple weeks later it finally threw a EGR code and I was able to get it fixed. That's what sucks about these computer controlled vehicles. A Sensor could be starting to go out but you won't know until it completely fails.
#3
07-12-2005, 11:25 PM
Yes, Idle Air Bypass. I replaced it with a new one, same thing. What is wierd is that it is intermittent. I'll start it up tomorrow and it'll be fine.... for a while.
Problem with closed loop stuff is anything failing in the loop can look like anything else!
Regards,
Steve
ttlx
Problem with closed loop stuff is anything failing in the loop can look like anything else!
Regards,
Steve
ttlx
Originally Posted by Intel486
What is the IAB? Did you mean the IAC? If not, then I'd clean that out to see what it's like.
That TPS code was strange though and I'm surprised replacing it didn't fix your problem.
I was having trouble with my truck starting and no one could figure out what was wrong. It was a couple weeks later it finally threw a EGR code and I was able to get it fixed. That's what sucks about these computer controlled vehicles. A Sensor could be starting to go out but you won't know until it completely fails.
That TPS code was strange though and I'm surprised replacing it didn't fix your problem.
I was having trouble with my truck starting and no one could figure out what was wrong. It was a couple weeks later it finally threw a EGR code and I was able to get it fixed. That's what sucks about these computer controlled vehicles. A Sensor could be starting to go out but you won't know until it completely fails.