Santa FE SM (2001-06) :: Erratic Idle - Revs Up And Down From 1200 To 2600 RPM

Daughter's 2001 Santa Fe Delta V-6 2.5 engine, needed lower ball joints. Replaced the entire lower arms as more cost effective & actually a bit less work, for me anyway.

So While under it, see oil dripping down back of engine. Decided to replace valve cover gaskets. So I start to disconnect all the involved connectors, brackets etc to pull the Upper air intake to get to the rear cover.

While moving around, find most of the hoses & vac lines baked brittle and dried out and loose even tho clamped, so I replace all of those, plus the PCV valve., & the upper & lower radiator hoses as well. I only removed the upper 1/2 of the intake. I change out the cover gaskets, reassemble every thing, reconnect all the connectors. I noticed that some of the connectors could apparently be switched to other sensors, but since all the lines seemed so backed solid, they actually retained their positions to go back onto the proper sensors.(at least I hoped so & it seemed that way).

Anyway, every thing back together & tightened up, so I start it up & the idle is at about 3000 to 3400 RPMs. WTF? So I pop the throttle a couple of times by hand and finally it drops down to normal, then just as suddenly, it begins SEARCHING for lack of a better word, and starts racing upto 2600 rpm then drops to 1200 then up again then down again.

No check engine light or other idiot lights on. So I shut it down & check all the connections and hoses, nothing disconnected or left off or loose. I start it again, and it immediately begins running high & low searching for the idle again.

I shut it down again, and put the MacPro scanner on it and NO codes either set or pending. I next check the Haynes Manual I have for it, & the closest thing I can find to my problem says: Engine Lopes while idling or idles erratically 1) Vac leak 2) Leaking EGR 3)Air filt clogged 4) Fuel pump not delivering enough fuel 5) Leaking head gasket 6) Timing belt/sprockets worn 7) Camshaft lobes worn

By process of elimination, not #'s 2) According to service manual, there is no EGR valve on the 2.7, and I couldn't find one either, #3) Air Filter is new & clean, #4) ran fine before I worked on it & with the engine revving up to 34 or 3600 rpms, getting plenty of fuel, #5) Have had many head gasket problems over the years on many vehicles, never anything like this, and again, it ran fine until I worked on it #6 & 7) Doesn't seem to me to be a belt sprocket or cam shaft problem, as none of that was touched & again, it ran fine until I worked on it. This kind of narrows it down to #1, for me, but this is not like any vacuum leak I have ever come across in 45 years of auto repair. I have found & fixed many stumbling idles due to minor leaks but never had anything like this.

I next called a friend who owned an automotive machine shop & who I used to do work for, and now runs a highway dept garage for a municipality who has been a certified mechanic for many years, told him all the above & the only thing he could come up with was a MAJOR vacuum leak, like possibly the upper plenum gasket rolled up or got torn some how when I replaced the plenum and he suggested that I try a smoke test.

Scratching my head, I go back to the car, & break out my home made smoke machine that I use to successfully pinpoint leaks in emissions systems. I ran it for quite awhile, and found some light smoke leaking from somewhere down around the head, but due to the construction of the engine & no way to get the light to shine under the plenum, could only guess that he may have been right & that there may be a large leak down at the lower intake manifold to head gasket. Needless to say, I removed the upper plenum again, & this time also the manifold to heads, and the gaskets looked like they may possibly have leaked slightly between the ports, & quite possibly somewhere around the number 6 cylinder. So I cleaned the surfaces & am putting on the new gaskets that came in the set with the upper plenum to manifold gasket set.

My questions after relating all of this:

1) The 2 gaskets between the manifold & the cylinder heads have a blue stripe around all 3 cylinder port holes (appears to be some kind of sealant or factory applied silicone bead) & there are no markings of any kind anywhere on the gaskets, so do the blue stripes face DOWN to the heads or UP to the bottom of the intake manifold ?

2) Regardless of which way these stripes face, should I use any kind of high temp sealant around the port holes in addition to the gaskets, or just install them dry ?

3) Can the Idle Air Control on the Throttle Body Fail & affect the idle like the problem I am having, but NOT set a computer code ?

4) Can the Throttle Position Sensor affect the idle like this and NOT set a computer code?

5) I also found an electronic valve between the Air Intake & firewall, it is labeled PCV and has an OEM part number after that, I believe this to be the Purge Control Valve, which connects the TB to a plastic line which I believe runs down to the emissions canister under the vehicles front seats. Am I correct in thinking that even if this part had failed, it would have NOTHING to do with my erratic Idle problem, but would throw an emissions computer code?