Do you have problems with getting the idle down?

I have a Series 4 TII engine in my car, with a N/A throttle body flipped upside down. It has always idled around 1300-1500rpm hot.

I was puttering around on the car today and decided to pull the upper manifold off so I could access the air bypass screw and try to adjust the idle down. To my surprise, not only are all three throttle blades fully shut but the air bypass is fully shut too.

What gets me is, there is no apparent vacuum leak. By rights it shouldn't even be running, so a vacuum leak to get the idle that high up would be pretty loud.

The BAC area has been blocked off, there is no computer control for the idle at all. It's idling at about 40kpa, which is about 18" of vacuum I think.

 

Check your throttle linkage. I have mine idling high off the throttle linkage right now while i wait to muster up the will to take off the TB to set the idle right.

 

If you still have the oil metering pump lines connected, it can nearly idle off the air injection itself through them. Also the air bleeds leading to the injector sockets will make for a pretty solid idle air system.

 

The throttle cable has slack in it. (That's the FIRST thing I double-checked) The throttle plate stop screws are backed out so far that they don't even contact the linkage, too. You can't see air around the throttle plates, normally you can see at least a .002-.004" airgap.

Interesting on the oil injection nozzles. As it is, the nozzles in the manifold have been replaced by bolts siliconed in place, and the nozzles in the rotor housings have had the banjoes replaced with nuts. I thought the vacuum lines just went to an on/off valve, so I left them uncapped.

One thing I did note, I did find a vacuum port that had a cracked cap on it. But when I took it off and replaced it with the engine running, it had no noticable effect on the idle speed. So, apparently a wide-open 3mm vacuum port doesn't affect the idle speed to any noticable degree. It didn't make much noise, either, so it's still possible that there's a vacuum leak I guess. But it'd have to be a BIG one, and I don't see where. All vacuum ports are capped, plugged, or JB Welded solid, except for the old BAC port (brake booster source), the port above the ACV location (MAP source), and I do have the air bleed for the fuel injectors functional. Pinching that one shut with the engine running didn't make a noticable change in idle, either.

 

Possibly a ruptured brake booster diaphragm is leaking massive air into the intake system? About the only thing I can think of really.

 

I was thinking that too, but there is no loud hissing under the dash, and pinching off the vacuum hose doesn't affect idle.

The only hose I did not pinch-test was the one for the FPR. It's not drowning in fuel so I'm fairly confident that it's okay

 

did you remove the thermowax system on the TB? if you keep the thermowax/fast idle cam but remove the water hose, it will idle high. do the whole carb cleaner trick too.

Or you can try to rig up a pressure tester, something like www.boostpro.net/prodtester.html , universal tester at the bottom. You'd just have to figure out how to make it work with the n/a intake pipe.

what vacuum lines? the hoses on the oil metering pump injectors?

 

All been removed. The throttle plates are fully shut.

The current plan is to do a smoke test next time I have free time and we have the equipment out.

Yes, the nonexistent vacuum hoses on the remaining oil injectors. I was under the impression that they only used vacuum to open an internal valve. I could try capping them off again, it's only four nuts to remove the upper and get access to everything.

 

Man I love my IDA carb.

Peejay, get some carb cleaner and while the engine is running spray the carb cleaner all around the intake and parts that may be leaking. If the idle changes when you spray an area then you found your vacuum leak. Good luck.

 

Propane works way better than carb cleaner. Modern carb cleaner doesn't seem to be quite so flammable as it used to be.

That said, the engine is so indifferent to fuelling (I have idle at ~13:1, but it's also just as happy at ~9:1!) that I am not sure it would tell me much, unless I went in there and leaned it way out... but I can't do that yet, no USB-to-serial adapter for my new laptop. Hmm, should probably get that soon if I plan on changing the exhaust.

A smoke test WILL show you where any leaks are. Actually, I'm kind of hoping that it's a lower gasket leak, since it's leaking a little coolant anyway and I need to put it together *right*. (Long story, it involves using a modified 6 port lower gasket and no O-ring at the coolant passage, just silicone around the gasket edge)

 

pressure check works ok too, you basically take the cone filter off and put a plug in the intake hose. then you can take a hose and blow into it. compressed air works best, but you can blow into it and it still works.

it will not work on some of the stock cars particularly the t2 as it takes some of the sources for the solenoids from odd places

 

Official statement: I'm a dumbass.

But I discovered my error, so I'm a reformed dumbass.

The operative clue above was that I'd reused a six port intake manifold gasket.

Now, the gasket WILL fit. And if you do some minor trimming, it will not interfere anywhere.

However. The holes where the aux ports go is the main difference between the two, and those holes allow communication between the intake ports, and some casting depressions in the intake manifold just "inboard" of the secondary ports.

I knew this. I figured it wouldn't be a problem.

What I did not figure on, was that those depressions extended to the rotor housing area - where the intake gasket is unsupported.

So as the gasket kinda deformed over time, air was going from between the gasket and the hollow areas near the rotor housings, through to the gasket area where the 6 port's aux holes were, and then down into the secondary ports.

With a T2 intake manifold gasket (thanks again Mike for telling me about Worldpac - I got the gasket for about 1/8th the hassle that it would have been from the dealer, in under 24 hours, and significantly cheaper) it will idle anywhere I want to. I don't have a workable laptop so I can't retune the idle, but it's running awesome right now.

I set the idle to 1200, because it sounds much nicer as a brap-brap-brap than a stut-ut-ut-ut at 900-1000ish. (Yeah my streetport braps on hot idle. WHO WANTS TO TOUCH ME? )

 

A two second squirt of carb cleaner around the intake, like I mentioned, would have found that.

Well, at least you found it and it's fixed now.

 

Actually, it probably would not have... I sprayed tire solution at that area and pressurized it with shop air and no bubbles.

And with the leaks anyway adding fuel didn't change the idle very much. So I leaned the idle out to the point where pumping the brakes didn't make the engine rev up. (Might as well take advantage of that indifference to mixture, and burn less fuel)

http://www.youtube.com/watch?v=c2n7F452CJU

It idles a bit happier now And when it's dead cold, it will idle at 700... instead of requiring lots of work to keep it from stalling.

 

Idles pretty damn smooth. Good job peejay. Was the 6-port gasket used for its metal qualities or simply "shallow pockets racing"? lol

 

It's stupid

It dates back to me not being able to get the proper intake gasket in time, plus when I originally put the engine in the car, I didn't have a workable TII manifold ported and de-crusted and adapted and ready to go, so I just threw on my GSL-SE intake manifold, which also happened to have a brand new gasket.

GSL-SE gaskets don't have cutouts for the coolant O-rings since they didn't have them. So when I put it on, I just siliconed the gasket heavily to the engine. When I had the TII manifold ready to go, I pulled the GSL-SE manifold off, saw the gasket was still firmly attached to the block, and just stuffed the manifold on over it. Only had a half hour to work on it, and all I suspect that having the load relieved from it is what allowed it to start leaking. Very, very minor coolant leak, at that.

The engine is totally smooth driving now. It doesn't buck or stutter *at all* when cruising down the road. I may have to open the intake ports a bit earlier, I was so used to having something that didn't like 5% throttle What is really funny is that as improperly as the engine was running with the vacuum leaks, it was running much much worse with the -SE manifold. It barely wanted to run at all unless the secondary ports were open. Lots of stuttering, bucking, general unhappiness. Massive port mismatch and soda straw runners + big port timing will do that, I guess But it ran well enough to get me running down the road...

Too bad I won't have time to do the exhaust work before dyno day. But on the bright side, I may not need to do the 75mm throttle body thing anymore.