High Idle Problem

[Demps]

Bottom is background:

I've been waiting to pull my plenum to re-route the vacuum canister line to the correct place and check/tighten the vacuum system. I finally pulled it a couple weeks ago. The vacuum pump was cyling every 4-5 seconds for about a second. AND, it had the idle issue still--more so when it is cold outside and it did not seem mechanical. The MAP hose cleaning helped until it turned cold.

As I pulled the plenum, I noticed the purge canister line that's attached under the throttle body hanging loose on the other end. Also, the line I was re-routing on the back passenger side of the plenum was out of it's rubber receptical. A little bit of goo and a little bit of gasket material, they were fixed. Replaced the vacuum reservoir and tightened the lines into it. Tested the actuators (which were on backwards), and the right on was binding and needed 12 psi to open. The driver's opened with around 9 psi if I remember correctly. Tested them (black boot=6psi to fully open), turned them over and they pulled the butterflies open with 7 psi per side. As a side note, the red actuator I got took 7.5psi to open fully not attached. Put it back together and the pump cycles every 10-12 sec for .5 sec or so. The idle problem, for two weeks of driving, is gone. Not like before, but gone. The full on power is (probably in my mind) noticeably different. The car cannot be floored in first from any rpm without spinning the tires.

I suspected the purge canister check valve from doing some svc manual diagnosis. Turned out it was the lines. For those with high idle then steadies out, I would recommend the test procedure. Car almost seems to idle too low. I reset the IAC by the scv manual procedure as well.

I hope this helps someone,
ted


----- Original Message -----
From: Ted Dempsey
To: ZR1GOLD@LISTSERV.CORVETTEMUSEUM.COM
Sent: Sunday, May 05, 2002 10:14 PM
Subject: [ZR1GOLD] TECH: Idle problem (maybe)


Before my last deployment I had an intermittent idle "flare" problem. Lots of folks offered suggestions as to the cause and some said they'd chased this demon as well. They asked that I post any findings. Well after 50 days of being gone I'm back at it.

SYMPTOM: Come to a stop and the idle would hang up around 1200 rpms then about 5-10 secs return to normal 750-800ish rpms (without blipping the throttle).

FIRST ATTEMPT: Cleaned and reset IAC valve. No joy.

NEXT ATTEMPT: I ordered the revised prom (which the car already had 9008--sidenote, the other one had 9012) after switching out chips between cars. This is an all together different story. Both the "new" chip and the two old ones had fewer occurances but still some.

LAST ATTEMPT: I pulled the MAP sensor and hose off the car. Cleaned the hose of oil with compressed air and q-tips. I noticed a loose piece of rubber on the "nipple" that connects to the MAP--could it inhibit the vacuum? I removed it and went for a quick drive. My fingers are crossed because it dropped to idle (800rpm) each time.

We'll see. Anyone who's idle stays high then returns to normal should clean this hose to just see--i.e. help me see if I'm crazy or not.

cheers,
ted

 

[kabnvtt]

Hey demps I have noticed the same problem with my Z. As soon as it stops raining I will give that a shot, thanks for the great info

Billy.

 

[rkreigh]

target idle on the stock chips is I believe 663. it does seem kinda to low, and my cars seem to idle a bit better above 750. a custom chip can raise it a bit. I chose 800 on the last burn we did, and I liked it better.

the power steering and Alt seem to work just a bit better and the car runs smoother.

nice write up Ted!!!

 

[kabnvtt]

Ok Demps I did what you did and it comes right back down to idle no more of that 3-5 second high idle, It only seemed to do it after slowing down from cruising speed though, if it was stop and go it seemed ok, but now it is perfect. Thanks again for the great free fix.
Billy