4.0 ohv high idle problems

[Pyromancer]

Engine is in a 94 Mazda b4000. Engine is a rebuild from jasper not sure how many miles are on it. It uses the 8 bolt flywheel but the intake and everything matches an early ranger or explorer, I dont have an other b4000 to compare. Idle sits at around 900-1000 rpm. Unplugging the IAC does nothing, unplugging the TPS does nothing as well. I have tried swapping both of these. I built a smoke tester out of an old soldering iron and a bike pump no vacuum leaks. I have adjusted the diesel/idle screw and I cant get the rpm to drop anymore even with it backed all the way out. IAC gets 12v with the key on and goes up to 14.4 with the truck running. The first two wires on the TPS get around .8V. I have also replaced the egr, the O2 sensors, cleaned the MAF, replaced the coolant temp sensors. Did the glove on the radiator test to look for bounce to see if I had a cracked head.

I have read a lot of threads on high idle and I am scratching my head on what else I could try. No CEL codes.

 

[Craig0320]

If you unplugged your iac and it does nothing then you have a vacuum leak. Change your pcv valve and see what happens. A smoke test won't tell you when they are bad. When they go bad they send unmeterd air into the intake thus causing the high idle. Whenever you unplug your iac the engine should idle way down and almost stall. Idle on the 4.0 tps is usually around .94-96v. If it is on .8v then it should be idling a lot lower.

 

[Pyromancer]

If you unplugged your iac and it does nothing then you have a vacuum leak. Change your pcv valve and see what happens. A smoke test won't tell you when they are bad. When they go bad they send unmeterd air into the intake thus causing the high idle. Whenever you unplug your iac the engine should idle way down and almost stall. Idle on the 4.0 tps is usually around .94-96v. If it is on .8v then it should be idling a lot lower.

PCV is brand new as well and moves fine.

 

[Vincenthdfan]

Been there, done that....read my thread of frustration and what I did to solve it.

http://www.therangerstation.com/forums/showthread.php?t=177005

 

[Pyromancer]

Been there, done that....read my thread of frustration and what I did to solve it.

http://www.therangerstation.com/forums/showthread.php?t=177005

Just read all that. Man glad you figured it out. I was having some surging issues at around 1500-2000 rpm so already replaced the fuel filter and furl pump. Seems to have gone away after that. Also found out my fill hose was leaking so did that as well. I haven’t touched the throttle body... I’m not a fan of Rockauto, they just tried to screw me on a return. Said they would cover shipping in one direction when I got the wrong flywheel and then charging me a “restocking fee” equal to the shipping on the return. Had to file a complaint with PayPal, worst customer service I have ever dealt with. Maybe I will see about amazon or something, where they have decent returns.

 

[Pyromancer]

Vincenthdfan thanks for sharing that thread.

I replaced the throttle body with one from a junkyard last weekend. Old one the plenum didn't seal around the edges. Idle is now at 600rpm. Unplugging the IAC doesn't seem to do anything still but I'm not sure I would notice a drop from 600rpm to 500rpm quickly. Truck has a little bit of a shimmy sometimes at around 1500rpm on the highway, but I cant tell if it is the engine or something else like the tires.