FINALLY FOUND THE CAUSE of my low idle!!!
 

After many weekends of fcuking around, testing the ignition, CHT, fuel pressure, mapping my AFM, ICV/ISV etc etc... the problem turns out to be a massive vacuum leak around the intake manifold's #1, #2 and #3 Runners. This has resulted in an extremely lean idle mixture, causing my car to idle ver low (300 rpms) for 3-5 seconds and stall :(

I bought some "proper" carby cleaner and flooded the area where these runners mate with the head and low'n'behold, idle climbs, she idles perfectly and doesn't stall at all :cool:

The right side of the manifold seems OK and made no noticable difference to idle quality, so the problem seems to be isolated to the left side only :( After a few seconds idling by herself, I can literally see the carb cleaner being sucked into the inlet, leaving the entire area completely DRY!!! :eek:

A word of advice to other young players: DO NOT USE WD40 TO TEST FOR VACUUM LEAKS IN THIS AREA!!! :mad: :mad: :mad: Had I used proper Carby & Throttle Body Cleaner, I would have identified the root cause of my problems many moons ago :mad:

NOW for the painstaking process of ripping off the complete intake manifold and replacing all 12 inlet gaskets.

Any advice for a first timer doing this R&R job before I begin???

Thanks again to all for their ideas/suggestions/advice, especially Souk who gave me invaluable advice via many e-mails every step of the diagnostic route :cool: SmileWavy

Save yourself having to the job again, replace the insulator/spacer as well, that is where your problem might lie. They are made out "bakelite" or something like that and are notorious for not sealing well. Plus, they are cheap!

Congrats on chasing your problem down!

Cheers

Good suggestion Jeff. I don't want to be chasing down a problem like this in another 12 months or so. I'll replace the whole lot just to be safe.

Strange though, my engine was completely rebuilt only 18 months ago, so I'm actually quite surprised these gaskets have gone already :mad: Unless of course my ex-mechanic didn't replace them with new ones, or didn't torque the inlet manifold down properly. Wouldn't surprise me :mad:

This job is easier with the motor out of the car. I have heard it can be done with a partial drop. Based on my experience I would not recommend it.

Be sure you have the proper tools (swivel sockets and a torque wrench)

While you have the motor out is what kills you...

-Clean engine compartment
-adjust valves
-replace the typical seals that leak on the top side of the engine
-replace all vacuum hoses
-replace fuel injector seals
-New clutch
-replace sound pad

I think you get the picture

The spacer blocks are not included in gasket kits. My guess is that the gaskets were probably fine, but the blocks were not replaced. Of course it is just a guess as I have not seen your motor. :) But it is a commonly overlooked item. Some people try to true them up with sandpaper on a flat surface etc., but for what they cost it just does not seem worth it to me.

Good luck, hope it solves the issue!

Cheers

Hind sight is 20/20....but that's the first thing ya check when ya gots a hunting or low idle.....but hey gud on ya that ya found it.

A bud uses a low pressure wand with a pressure rheostat hooked to a propane tank.....I always use carb cleaner or ether/quick start.

Merv,
Its not too much of a job. Just git the allens on each runner. As I remember it helps to have the AFM out of the way for the pass side. Also the rubber boot above the throttle body needs to come off too.
Be very careful about dropping anything in the inlets when the runners are off.
Note that there are 2 gaskets per runner, one on each side of the insulating block.

Cool, thanks guys ;)

It's definately the problem b/c the carb cleaner gets sucked into the base of the runner(s) and the idle climbs and remains rock steady until the carb cleaner is completely induced.

I won't be dropping the engine to do this. Don't have the space or know-how (yet)! LOL!

Will I have to remove the fuel rails etc, or can I just disconnect the fuel lines & injector loom and lift the whole intake off?

Is it worth removing the injectors and cleaning them out? How would I do this? Pass compressed air through them, or send them out for professional cleaning? Is there a solution I can soak them in overnight or something?

Thanks in advance :)

WOOHOOO! Awesome Merv! Glad you got it figured out. If you haven't already pulled the intake off, I might suggest tightening the barrel nuts. The paper gaskets compress over time, and since you put new ones on with the rebuild, they probably just need to be torqued again. Worst case (2 actually) you blew out the paper gaskets under boost, or the insulators are cracked. But it's worth doing the simpler thing first.

You can get to the bolts w/o dropping the engine. It's not the easiest thing to do, but it's possible with patience ans some socket extensions. Some of them you'll just have to us a L-allen wrench. Witht he IC and meter removed you'll have as much of a shot at them as if the engine were out.

Souk said it: Try tightening up first.
Swivel-sockets, short Allen keys, Torque wrench and patience.

I just had the intake manifolds off to replace the $361 fuel line. My 88 cab should be similar to your 89.

You don't need to remove the fuel rails from the manifold just unplug the injectors to get the wire harness out of the way.

The biggest hassle was getting the lower gasket off the intake port on each head. You are working at a right angle because of the fiberglass duct sticks up about a half inch around the intake port. The baked on gaskets laughed at Permatex gasket remover. When you stick your head in there your eye is about two inches from what you are working on and my old eyes don't focus well that close up.

The speed and reference sender connectors are identical, mark which is which before you unplug them (wire ties on one?).

Mine had two springs that attach to the throttle linkage and the engine, another pain to get back on.

Now looking back on it I think it might have been just as easy to drop the engine.

l`ve never understood why people us WD-40 to check for vacuum leaks. Sorry you learned the hard way :)

Like suggested above try tightening first, then maybe try some sealant to bog up the join?

And if you do need to pull the mainfolds off - (I know it's stating the obvious) be so careful not to drop anything down there.

Thanks guys. I managed to lift the right side of the manifold off, HOWEVER, I think the rear washer (which was stuck from corrosion) from the #6 runner popped off when I lifted the manifold to loosen it. And I think it fell into the intake! FOR FCUK SAKE!!! That's the last thing I need!

Is there an easy way to extract this? Special flexible magnetic tool or something? Stressing real bad here :mad: :confused: :(

First off look down in there. Is the valve open? Sure it didn't just fall under the shroud. If you can see it you are home free (as in retrieve it).

If it is open I would try massive amounts of compressed air through the spark plug hole.

Relax Merv....a small magnet will fish it out. Duct tape on the end of a flexible wire may get it out too.

Is the intake valve open on #6? If not....it'll be very easy to get the washer out. If it's open,and the washer went into the chamber, you'll just have to work at it a little. It helps to know what position your valves are at...The key is not to freak out, and don't go spinning the crank by hand until you know where the cylinder is in its cycle. You don't want to crunch the washer in the chamber if it is in there.

Merv,
We are here deciding on the wine for the Christmas party, tis a hard life, and while deliberating will suggest a small mirror, dental size and a telescoping magnet. Hope the washer is steel, I think so but check the others with a magnet.

Be sure to get this washer before it gets you by slipping by the valve.

Realise it may have not fallen in.

But you must find it before doing anything else.

the N Z wine won the test, called Tofu or something like that.

Thanks guys. I'll ckeck the position of the valves on #6 and see what I can do. Hopefully I can just use a magnet/duct tape to extract it, otherwise, I guess I can connect up an air compressor and run 100psi through the plug hole and pray that it comes out! Grrrr!

Oh, I also noticed that I can actually lift the right manifold up high enough to replace the gaskets/spacers without removing fuel lines etc.

First thing's first tho, damn washer! LOL!

EDIT: One thing is certain, I had a couple small vacuum leaks on the right side manifold too cause I can see where the carb cleaner seeped into the inlet. Gaskets are wet. No wonder I was having poor drivability issues for the last few months :eek:

Merv, I did this operation a few years ago, and I also dropped a washer into one of the intakes(along with a few crumbs of old gasket material). I rigged up a length of fuel line to our venerable Electrolux vacuum with some duct tape and voila, up came the washer and later some little crumb bits stuck to the fuel/vacuum device. Good luck! Glenn

Hi Glenn. Thanks for the suggestion. I too was thinking of using my vacuum cleaner to suck it up :confused: