Very High Idle

[Gunny]

Originally Posted by RussMcB

... I removed the (very restrictive) Borla resonator and inserted a SW X-pipe (purchased with ZR-1 Registry discount).

removing the resonator should make a HUGE difference !!!

What size SW X-pipe? 2.5 or 3.0? or do they make a 2.75 which should have been a direct fit?

apologies for continuing off-topic conversation about exhausts ... now back on track -- be sure to double check the vac. connections at the back of the plenum. Easy to check, esp. with a flashlight and your hand ... if any of the lines are loose, it will make a big difference.

[RussMcB]

Originally Posted by Gunny

removing the resonator should make a HUGE difference !!!

What size SW X-pipe? 2.5 or 3.0? or do they make a 2.75 which should have been a direct fit?

I bought their 3". I don't think they offered a 2.75".

Isn't it hard to believe Borla's resonator for the ZR-1 had such small inlets and outlets? I can only guess they must've just wanted to use something they already had on their shelves.

Thanks for the vacuum leak suggestions. I'm hoping to have time tonight to spend under the hood.

[Billy Mild]

Do you have a vacuum gauge or mityvac for testing?

[RussMcB]

Originally Posted by Billy Mild

Do you have a vacuum gauge or mityvac for testing?

I do (both). So, is it simply building vacuum, seeing if it holds, and trying to find where it's leaking?

Tonight I only had 5 minutes to glance around in the engine bay, hoping to see an obvious problem. Everything visible seemed attached. I do have one section of very poor quality hose that needs to be replaced (attached to cruise control component, I believe).

[Billy Mild]

Hook the mityvac to the same vacuum line the vacuum pump is connected too. See if this Holds vacuum for longer than 15 minutes. Then you start pulling vacuum on the other line that are connected to the plenum.b

[Paul Workman]

Assuming the issue is an air leak, the sources to consider are:

• The vacuum nipples located in the middle of the plenum; one on each side.
• The plenum gasket
• The IH gasket
• Injector "O" rings
• TB gasket
• TB Idle Air Control (IAC) malfunction
• TB main throttle plates ajar
• Power brake booster
• Fuel pressure regulator
• PVC evacuation line
• Evap canister evacuation line

With exception of the gaskets and "O" rings little disassembly, this should help:

1990 FSM, but later models are substantially similar:

[mike100]

I second secondchances recommendation to put a book or something that won't collapse in front of the airhorn while the engine is running. If it doesn't stall, the source of the air leak will pretty much be revealed audibly. Even though you may not see it, you can fish around with a long vacuum line stuck in your ear and the other end under the plenum until you can find the place where the air is rushing in.

[RussMcB]

Thank you. These great responses are really appreciated.

FYI - When I wired open my secondaries (and got Marc's chip), I eliminated my vacuum pump in the right front. That's what most people do, right?

[RussMcB]

Friday 6PM update...

Got home from work, ready to start working on the car and now it's idling at 900 RPM (!).

Geez. Not sure what to do now. :-)

I'll give it a test drive and see if anything changes. Maybe I'll play with Cliff's new code reader tester that arrived in the mail today...

[Paul Workman]

Ooooo! Me hates it when that happens! Nothing like the intermittent gremlin to make ya pull out yer hair (and I don't have much of mine left!).

Well, good luck.