High searching Idle - Page 2 - ZR-1 Net Registry Forums

jss06c6 · 02-09-2018

Ok, that's clearer..

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jss06c6 · 02-09-2018

Old one on the bottom, new one on the top..[ATTACH]

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jss06c6 · 02-10-2018

Put the new PCV connector on. Guarantee no leaks there! It's darned tight! Fired up the engine. High idle 1300 rpm, until closed loop kicked in. Dramatic swings in AFR as fueling was dithered. Finally settled down at full coolant temp (193F). Idle still sits at 1175 versus commanded 750. IAC locked at 0 trying to adjust idle to commanded. Verified IAC working. Stepper motor kicked in at 1325 room (4), then rises with increase in rpm. Now suspect something went wrong in the TB. I'll put a borescope under the plenum just to make sure no other vacuum connections are off. Then I'll pull the bellows off and use the borescope to look closely at the TB blades during idle and increasing rpm.

Steve

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A26B · 02-10-2018

Sounds alot like the MAP hose. Off, broken connector, or plain rubber line with low point oil collection in low point. The rubber connectors on each end of the hard plastic pipe are prone to tear due to age. If you can reach, remove the MAP hose from the plenum barb & put your finger over the barb to see if the high idle is due to the MAP hose.

The lower dual PCV hose in mine (94 w/57k) was rock hard on the side towards the firewall & completely rotten on engine side.

XfireZ51 · 02-10-2018

Quote:

Originally Posted by jss06c6

Old one on the bottom, new one on the top..[ATTACH]

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U can easily see how out of shape the old one is v the new one.

jss06c6 · 02-10-2018

Quote:

Originally Posted by A26B

Sounds alot like the MAP hose. Off, broken connector, or plain rubber line with low point oil collection in low point. The rubber connectors on each end of the hard plastic pipe are prone to tear due to age. If you can reach, remove the MAP hose from the plenum barb & put your finger over the barb to see if the high idle is due to the MAP hose.

The lower dual PCV hose in mine (94 w/57k) was rock hard on the side towards the firewall & completely rotten on engine side.

Jerry,

The MAP hose is not off, nor broken. Checked that again this morning. The connections are tight, including the 90 degree fitting on the bottom of the MAP sensor. I'll pull it to make sure it's clean however.

I also checked the PCV hose while replacing the top fitting. Pliable and tight. No issues that I see there.

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jss06c6 · 02-10-2018

Quote:

Originally Posted by XfireZ51

U can easily see how out of shape the old one is v the new one.

Yes, agreed, but replacing it had no effect on the problem. Going to check under plenum with borescope for all the usual suspects and check the TB as well.

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Ccmano · 02-10-2018

At the risk of stating the obvious. You checked both MAP sensors, right?
H

XfireZ51 · 02-10-2018

Quote:

Originally Posted by jss06c6

Yes, agreed, but replacing it had no effect on the problem. Going to check under plenum with borescope for all the usual suspects and check the TB as well.

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Have u done the ole 3ring binder in front of the TB trick yet?
Could point to either vacuum leak, or TB issue.

jss06c6 · 02-10-2018

Not yet but definitely part of the diagnosis..

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02-09-2018	#11
jss06c6 Join Date: Aug 2015 Location: Magnolia, Texas Posts: 884	Re: High searching Idle Ok, that's clearer.. Sent from my XT1585 using ZR-1 Net Registry mobile app

02-10-2018	#13
jss06c6 Join Date: Aug 2015 Location: Magnolia, Texas Posts: 884	Re: High searching Idle Put the new PCV connector on. Guarantee no leaks there! It's darned tight! Fired up the engine. High idle 1300 rpm, until closed loop kicked in. Dramatic swings in AFR as fueling was dithered. Finally settled down at full coolant temp (193F). Idle still sits at 1175 versus commanded 750. IAC locked at 0 trying to adjust idle to commanded. Verified IAC working. Stepper motor kicked in at 1325 room (4), then rises with increase in rpm. Now suspect something went wrong in the TB. I'll put a borescope under the plenum just to make sure no other vacuum connections are off. Then I'll pull the bellows off and use the borescope to look closely at the TB blades during idle and increasing rpm. Steve Sent from my QTAIR7 using ZR-1 Net Registry mobile app

02-10-2018	#14
A26B Join Date: Dec 2003 Location: Arcadia,OK Posts: 3,394	Re: High searching Idle Sounds alot like the MAP hose. Off, broken connector, or plain rubber line with low point oil collection in low point. The rubber connectors on each end of the hard plastic pipe are prone to tear due to age. If you can reach, remove the MAP hose from the plenum barb & put your finger over the barb to see if the high idle is due to the MAP hose. The lower dual PCV hose in mine (94 w/57k) was rock hard on the side towards the firewall & completely rotten on engine side. __________________ Jerry Downey JERRYS LT5 GASKETS & PARTS http://www.jerrysgaskets.com 1994 *ZR-1, Black/Black, Lingenfelter Aerobody, 416cu in, 3.91 gears, coil-over susp, Brembo brakes, etc. 2016 Black-Red, 3LT-Z51 Auto 8-speed. Last edited by A26B; 02-10-2018 at 09:28 AM.*

02-10-2018	#18
Ccmano Join Date: Jun 2006 Location: Sparks, NV Posts: 2,852	Re: High searching Idle At the risk of stating the obvious. You checked both MAP sensors, right? H __________________ 90'ZR-1 #1461 Red/Black Ported Intake, Degreed Cams, OBX Headers & Exhaust, Fidanza FW, Secondary Delete, Custom tune, C6 GS Wheels. Sold 08 C6 Z51 Crystal Red Metallic Sold Vararam Intake, Tune, Sold 05 C6 Z51 Red/Black Sold 90'ZR-1 #1723 Black/Gray Sold but not forgotten 91' Z51 L98 White Vert. My First, you always remember your first. Sold.

02-10-2018	#20
jss06c6 Join Date: Aug 2015 Location: Magnolia, Texas Posts: 884	Re: High searching Idle Not yet but definitely part of the diagnosis.. Sent from my XT1585 using ZR-1 Net Registry mobile app