Bouncing / High Idle problem - 1999 Ranger 4.0 4x4 Auto

[redryder37]

My truck idles around 1,000 RPMs (after warming up) and seems to like to jump up and down. It will jump up to about 1500 RPM for a few seconds and then slowly drop back down to 1,000 RPM. I thought it was my AC causing the idle to increase and decrease so I unplugged it to check and it didn't seem to make any difference. I've replaced the TPS and cleaned the MAF sensor. Any ideas? Also, any ideas as to why it's idling so high? Really need to get it fixed today or tomorrow if possible. Thanks!

 

[redryder37]

Update

I ended up reading forums all evening trying to come up with something. Nothing though. I guess it's staying the way it is for now.

 

[racsan]

could be a vacuum leak somewhere causing a high idle. i had one & it was tough to find (ended up being my fuel rail gasket) at first i thought i had a sensor problem, replaced every sensor on it. i was down to changing out the main ecu or tearing down the top of the motor to look for a bad gasket. glad i went the "gasket" route first. also had a leaking valve cover gasket to deal with. a idle air control valve could also be a possibility if your motor uses one. mine has one, but its a '93 and im not sure if yours would have one.

 

[09fx4guy]

If it is a vacuum leak, spray a little carb cleaner near where you suspect a leak. It will draw in and the engine will idle a little higher for a moment or two. Thats how I found a lean on my 92. It turned out to be a cap missing off the vacuum tree. Be careful, it is a little dangerous, but if you use small puffs, you should be fine.

 

[freedom5]

If it is a vacuum leak, spray a little carb cleaner near where you suspect a leak. It will draw in and the engine will idle a little higher for a moment or two. Thats how I found a lean on my 92. It turned out to be a cap missing off the vacuum tree. Be careful, it is a little dangerous, but if you use small puffs, you should be fine.

You might also try backing off the mechanical throttle stop about 1/2 turn. The idle is controlled by the engine coolant temperature sensor but initially the mechanical stop will control the idle until the engine starts warming up and the ECS takes over. If the throttle stop is a bit high it will cause the engine to speed up momentarily (surge) like it does when the engine is cold even on a warm day if it has set for awhile.

freedom5

 

[kevinsranger]

check for cracks in the intake tube between the throttle body and maf, they like to dry rot and crack and cause that problem