high idle after tune up

96 ram 1500 4x4 5.2
Just recently gave big red a tune up...
Plugs
Wires
Cap
Rotor
Pick up
Coil
Oil change and filter
Air filter
And after tune up, I noticed that the idle was high (1170 -1200rpm). I read about IAC..., CLEANED port and replaced IAC motor with new one..still high. Replaced MAP sensor and TPS too (nearly 20s old). Idle still high. I then disconnected and plugged all vacuum lines and ports. Idle lowered to 810/850 rpm and purred like a kitten. I then started hooking up vacuum lines one by one to see if idle changed. All was good until I got to the last hose. I removed the plug in the hose going to the crankcase breather on top of the valve cover and voila...Idle went up to where it was before. I'm stumped...hoping someone can offer suggestions.

Were any of your plugs oil fouled or showed symptoms of oil fouling? That breather on top of the valve cover is the pcv valve. If your idle went up from the pcv line, your valve is just blowing through. Pull the pcv valve out of the valve cover and shake it. If it does not rattle, replace it for sure, other wise check for leaks around the valve or replace it.

MagSport said:

Were any of your plugs oil fouled or showed symptoms of oil fouling? That breather on top of the valve cover is the pcv valve. If your idle went up from the pcv line, your valve is just blowing through. Pull the pcv valve out of the valve cover and shake it. If it does not rattle, replace it for sure, other wise check for leaks around the valve or replace it.

Click to expand...

Some of the plugs looked suspect. The pcv valve is fine. It's the hose on the other side, that goes from the back of the air filter box to the crankcase breather. It has a **** ton of vacuum pulling on it.

OK...after searching around this forum, and others, I determined, with much confidence, that it was the plenum gasket failure. I ordered the kit from Hughes. It had everything that I needed and I couldn't be any more happier with the end result....problem SOLVED!!!

Awesome glad to see you're up and running.