Idle won't set lower than 1100rpm

[vristang]

I adjusted the idle today following these instructions. The idle adjusted out just fine at about 900rpm, which sounded pretty good considering the cam. I then adjusted the timing, because it was off, again following precisely the directions on the above site (except that I don't have my timing gun with me). When I adjusted the timing the idle increased. I figured no big deal I can just readjust the idle for the new timing.
Well, the idle screw is completely backed out and the idle is sitting at about 1100rpm. The timing is great, and the motor responds much better at low rpm. I have yet to wind the motor over 4k though.

Could this be due to the TPS?
It doesn't seem like it but I can't check the TPS yet since I don't have my meter with me.

Did I just miss a step?

 

[88 Fox GT]

Unplug the IAC. If the engine keeps running, you probably have a vacuum leak.

 

[emagdnim]

Yup my engine would idle at 1100 rpm with the IAC off it turned out to be a vacuum leak but the leak was in a spot impossible to find without taking off the intake.

 

[vristang]

Thanks for responding guys.

My thoughts automatically went to bad sensors, forgot all about the basics.

Between your recommendations and the sticky on surging idle I think I will have the problem licked by tomorrow night.
Any more thoughts are welcome though.

 

[HISSIN50]

Actually if setting the idle per that article, the car will idle without the IAC (at warm idle, no load or need for idle compensation).

Jason, you have a pretty non-stock set up, so I think some trial and error is going to need to occur to iron out the bugs. I do like your idea to check your timing for reference, as well as the TPS. A stockish motor pulls ~15-20" hg vac at idle. With your combo, I could not even guess (only you know what your cam's characteristics are. Most of the time double-digit-vac is sufficient).
I really would probably hold-off on much else till you can toss the light on and check timing and note the TPS value (though I bet the latter is fine).

Sorry to not have any great ideas. A note: I would keep resetting the KAM as you go, so you are not dealing with stored adaptive settings. Otherwise that can really delay seeing how a change affected the performance.

Good luck bud.

 

[vristang]

Hissin50 I hoped to hear from you. I did get some ideas from you but will need to get a vac gauge first. I am sure it will be worth it.

Well I thought I just had to figure out the idle, but the oil control issues have come back. I'll put that in another thread though.

I pulled into the garage adjusted the TPS from .88 to .99 I also checked the TPS value at WOT = 4.66, does this sound ok?
While the engine was running I sprayed starting fluid looking for a leak, no luck.
Then I cleaned the MAF with TB cleaner since it was visibly dirty. I went to adjust the timing, but remembered that the last time I pulled the timing cover I had completely destroyed the pointer, so that will have to wait til Friday.

I also cleaned out the IAC valve. I have some issues with this though. It seems to me that it was designed wrong for an electronic controled idle. Here's what I mean, when vac is high it seems that the vac would pull the valve open. I would imagine this is fine if you have engine vac that is close to the stock 50. But if vac is much higher (and I think it could be with a stroker?) it will pull that valve completely open, and bypass the electronic control. I will try to mount the IAC upside down as the "Surging idle" sticky suggests this for some combinations. I didn't tonight because of hood clearance, which means I have to get creative.

Other than timing I don't know what else to check. Friday I will be pulling heads for what is most likely bad valve guides. But I would like to keep trying to sort out the idle issue until I pull the heads.

Thanks for all the help It is appreciated.

 

[vristang]

Anyone out there have to mount the IAC upside down on a 351w?

How did you resolve hood clearance?

 

[jrichker]

I have tried mounting the IAC with the wiring connector pointed towards the center of the engine and was not able to get satisfactory results. The IAC didn't seem to control the idle like it should.

 

[vristang]

I have tried mounting the IAC with the wiring connector pointed towards the center of the engine and was not able to get satisfactory results. The IAC didn't seem to control the idle like it should.

Thanks for the feedback.

 

[vristang]

I just wanted to let you guys know what the outcome was.
Turns out that the idle issue and the oil in the intake were from the same problem. The intake gasket had slipped down when I installed the lwr manifold.

Vac leaks are tough to find, when they are through the crankcase!

Click here for pic #1

Click here for pic #2