No run with air tube removed...

I just picked up a 2nd 1994 Mk8. It was T-boned, so it'll be my "donor" car (and nope, I won't be selling off any parts. Sorry.)

I'm getting plenty of play time under the hood, and learning alot. I'd like to work on a true cowl induction setup on my driver, so that means a complete rework of the air tube/ MAF / filter assembly.

Car runs great with everything hooked up, but if I remove the air tube at the throttle body, the car will not idle. With everything installed, disconnecting any of the sensors installed in the air tube does nothing to affect the idle, to include the MAF electrical plug. It even still idles if I completely remove the air cleaner / MAF assy but leave the rest of the tube attached to the TB! But open a big hole in the tube (such as removing the air silencer that drapes over the driver's valve cover) and she won't idle.

What....is up....wit dat?

RE: No run with air tube removed...

I figure that the motor warmed up enough for the computer to finally begin to fine tune the air/fuel mixture. But when it started to tweak on the knobs, all the data from MAS and air temp said that the motor wasn’t running efficiently. So it adjusted the fuel mix to try to correct the situation. But without the proper feedback, the end result was terrible.

You gotta have air flow through the MAS.

RE: No run with air tube removed...

You're gonna probably need to to something with the IAC(Idle Air Control) valve. Think of it as a throttle plate bypass. You're removal of the intake tube changes the vacuum 'resistance' at the IAC which either then flows too much air or too little air to maintain idle.

Good luck with your project!

RE: No run with air tube removed...

The computer is looking for a MAF signal to know how much fuel to pump in. If you lose the MAF, it will probably try to run from known values. If it knows that 0% throttle generally means x amount of fuel, that's how much fuel it will pump with no MAF signal at idle. If you unplug the whole tube, the tb is breathing more freely and the mixture changes.

Bottom line, who knows what it's going to do when you start unhooking things it needs to run. Don't expect it to do anything. If it starts, sputters, and dies, without a MAF or air tube it doesn't mean anything, except that the motor isn't frozen.

RE: No run with air tube removed...

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You're gonna probably need to to something with the IAC(Idle Air Control) valve. Think of it as a throttle plate bypass. You're removal of the intake tube changes the vacuum 'resistance' at the IAC which either then flows too much air or too little air to maintain idle. Good luck with your project!
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It really seems to be dependent on "resistance" as you say, at least that's what I seem to be experiencing here. Granted, the MAF is very important in the system (esp. when actually driving!), but just letting it idle, my car would still run with the MAF removed but the rest of the intake tube installed. Remove it all (thus removing "resistance") and it won't run unless you keep a foot on the gas.

What I need to do is get the hood out of the way, build a short intake tube to include MAF/ filter / other sensors and then see what we got. I agree I'll probably still have to do something with the IAC, but what, exactly, is the question....

RE: No run with air tube removed...

Build a tube to the MAF with a fitting for a hose after the MAF. run the hose from the fitting to the IAC. The IAC should be drawing metered air.

RE: No run with air tube removed...

All I know from the old school is the difference between idling and not running is very, very little(be it fuel or air). So little is required just a slight change in either can be enough to stall it out.

Considering how the PCM strategies operate, the question THEN becomes is it stalling in warm idle or cold idle or both?

You may get more insight reading here... http://fordfuelinjection.com/index.php?p=64