Tadi

Ok, I've done plenty of searching and reading on this so I think I know what's going on, but I'd like a quick sanity check from the group here to make sure. Here's the situation.

86 951, APE chips, LBE, otherwise pretty much stock. The car runs well when driving, no hesitation or misfiring. I can cruise at 75mph with no drama whatsoever. It pulls hard when under boost.

When I start the car, it starts right up and normally settles into a decent 900ish RPM idle and then will stumble a bit and recover. Once it's warmed up a bit the situation is much better. However, whenever I'm driving and depress the clutch to come to a stop the RPMs will drop like a rock (normal) and head past the 900 RPM mark and stumble around a bit down in the 600-700 range. Sometimes it will normalize and hold 900, other times it will stumble around for a bit. The car never stalls, just a sort of rough idle of sorts. When this is happening, the boost/vac gauge shows ~10-12Hg/in vacuum vs. the normal 16ish Hg/in of vacuum when it's idling correctly.

Tonight I took some time to insure the idle was set properly using the normal idle set routing, and I noticed that when I disabled the ISV it was running a little rougher than usual. So I went to adjust the idle to compensate and found that CLOSING the idle adjustment screw allowed the idle to settle into the normal range.

So, my theory is that I have a vacuum leak somewhere. My thinking is that there is a vacuum leak after the AFM that's causing the car to run lean when in the idle fuel maps and by closing the throttle adjustment screw I'm compensating for that vacuum leak by reducing the amount of air coming past the throttle plate. Does that make sense?

I have a full vacuum hose kit and venturi delete kit waiting to be installed, just need to get a decent block of time to pull the intake manifold. Oh, and I verified that the TPS adjustment is correct (clicks right as the throttle cracks open). Could it be that the ISV is stuck open? I haven't bench tested it yet but I plan to do it when I pull the manifold to replace all the vacuum lines.

Any other opinions/ideas?

eman930

I'd start with replacing all your vac and your venturi delete kit, best move I ever made. I can almost grantee you'll find a broken vac line while doing those. I'm still fighting some tuning issues myself, I just did a boost leak check, my throttle body is leaking a large amount from the butterfly shaft seals, like a good 5psi leak. You might wanna get a reseal kit for your throttle body as well.

Tadi

I cleaned out the throttle body tonight and it was very dirty. I also have a throttle body rebuild kit waiting to be installed. I think I may try to pressurize the intake tomorrow before replacing all the lines just to confirm the problem, but I'll definitely be rebuilding the throttle body.

eman930

I used a 2" PCV pipe cap and my old intercooler pipe to throttle body rubber coupler, regulated line pressure to about 15psi, instantly found the leak at my throttle body, I could hold my hand like 2 inches away from the throttle body and feel the air blowing on it that's how big it was. When I pulled The throttle body the shaft seals just crumbled in my hand.