Oil in 4.6 Throttle Body and Intake, sticky throttle

I just replaced the (cracked) intake on my 2000 GT with an aftermarket one of the newer aluminum coolant crossover design, and I saw lots of baked on oil sludge in my throttle body, the factory intake manifold, and in the runners into the heads. The runners were clean below the injector's spray pattern.

I've also noted that my throttle is sticking when I first press the accelerator pedal, for the past couple of months, and I can hear the valves rattling as if the octane is too low in the gas. I had to replace the IAC valve a while back and even earlier had to clean a lot of sludge out of the factory original, as it wouldn’t hold idle.

Finally, I don't have any leaks on the garage floor, and I don't see any smoke from the exhaust, but I am using about 1.5 quarts of 5w-30 consistently between oil changes.

I've got about 137,000 miles on the 'stang, and I am the original owner.

Is this possibly an issue with a faulty PCV valve, or are these symptoms of something else on the intake side?

Thanks in advance.

trinity_gt said:

The PCV system feeds crankcase oil vapors back into the intake at the base of the upper plenum so some of the deposits are caused by that. The EGR system also feeds inert exhaust into the intake at the upper plenum and there will be some carbon from that. Combined with the oil fumes a build-up of slime on the intake runners is normal and isn't hurting anything..

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Thanks for answering, Trinity_GT.
I see more oil sludge than carbon, but a while back when I had to deal with the IAC valve issues, I saw more carbon. I've babied this car, by the way, regular oil changes, etc. Other than that it's been a daily driver, averaging less than 40 miles a day.

trinity_gt said:

Can you operate the throttle by hand to isolate where the sticking is occurring? Are the return springs in good shape?

Don't clean the throttle body by the way. There's a coating inside the bore around the throttle plate that helps to prevent air leaks at idle. Cleaning the bore can damage this coating leading to goofy idle problems...

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When I hand operate the throttle, I can feel it sticking "from idle" then it operates normally. It is the same kind of "catch" I feel in my right foot on the pedal from inside the car. I have not cleaned the throttle body, as I had also heard of the coating inside the bore, thanks for mentioning.

trinity_gt said:

What mods do you have (speciflcally, have you "tuned" the car with a handheld or mailorder tune) and what grade of fuel do you run?

FWIW, the rattle of detonation sounds like marbles in a tin can and can damage the engine internals.

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Only mod away from Stock is a Dorman replacement #615-175 intake manifold, which I just added over the weekend. It was to replace the factory one leaking coolant per the bad original design. I noted the sludge in the old manifold and throttle body during the swap. The "tune" is still the original factory programming, I haven't touched the computer.

I still run 87 Octane Regular gas, and the valve rattle I described is noticable only when the engine is "hot" and is "mild" if I had to describe it.

I had read that oil consumption through the intake can lower the Octane of the injected gas, so I wanted to mention the symptom.

trinity_gt said:

That sort of consumption rate might not produce smoke noticeable from the driver's seat. If you were to drive around in a car behind while a buddy drove your car you might see the odd puff from the the exhaust. My guess would be you're likely looking at oil getting past the valve seals/guides at that sort of mileage.

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Thanks, I'll have to let one of my friends drive the 'stang while I drive "chase" and look for smoke.

trinity_gt said:

Excess ring and bore wear can lead to excess blowby into the crankcase and an increase in oil vapor loading into the intake through the PCV.

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Yeah, I had hoped that since I had babied the GT that even at 137,000 or so miles that there wasn't too much wear in the rings, but it HAS been over 11 years since I bought her new...

Thanks again for your replies.

sneaky98gt said:

I destroyed a piston/ring in my car a little while back. Because that cylinder wasn't sealed up and holding compression, it was pressurizing the crankcase. This resulted in some oil going through the PCV system and getting on everything from the throttle body downwards, similar to what you are describing.

I'd go to your local auto store and borrow a compression tester, and see what you get on all 8 cylinders.

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Thanks sneaky98gt, I'll try to do a compression test and see what is going on in the cylinders.

BTW, I have Not noted any "miss" like a cylinder was going out; the GT idles smooth as silk, (probably could balance a coin on the top of the throttle body) and still runs very well through all the gears, and while crusing on the highway. Last I checked I was still getting about 23 MPG highway; haven't measured it since the intake manifold swap...