High Rev and Rough Idle Issues after Intake Gasket Repair

[nhkayaker17]

Hi I've read through the forum and couldn't find what I'm looking for.

I have a 2000 Ranger 4x4 4.0L and it started running very rough. My local shop replaced the plugs, plug wires, and ignition coils and it would fine for a while. I tested it beforehand with my OBD2 reader and it definitely has a vacuum leak.

Few months later it's back and I told the shop to look for a vacuum leak. Low and behold they found one in the lower intake manifold gasket. I replaced it all myself and when I turned it on it's running above 2000 RPMs and if I leave it on it creeps up to 3k.

I figured I did it wrong so I just gave up and brought it to a different shop. They call me 2 days later saying they replaced the gaskets again and it still has the issue. They cant figure it out. Awesome.

There is no CEL and no codes. I go it back and unplugged the IAC with no change. Did the same with the MAF and idle went down for about a minute then right back up.

Could his be a bad IAC or PCV? Bad MAF? I thought unplugging the IAC and MAF would've ruled them out as problems. Could the throttle body not be closing all the way? I'm at a loss and need some guidance. I'm pretty sure the issue is mechanical and not electrical but I'm a well known idiot and am often wrong.

 

[franklin2]

It still runs 2k-3k rpm with the IAC unplugged? You definitely have air coming in where it shouldn't be. Get some brake cleaner (the flammable kind) or something else the engine likes to run on With it idling and the IAC unplugged, start spraying it around. If you hear a change in how it runs, something is going on there in that area.

See if you have a convenient vacuum line you can pull off with it idling, and then spray the brake cleaner down in the engine a little bit to see how it reacts. Then you will know what to listen for when spraying it in different areas.

 

[rusty ol ranger]

Warped intake?

 

[RCC]

Definitely vacuum leak somewhere.
Since intake has been off try franklin2 method around manifold, plenum and throttle body. If no leak there, start checking

 

[RCC]

... every vacuum line again.
Sorry about split message.
Lost my internet connection momentarily.