Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > Porsche 911 Technical Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
Join Date: May 2019
Posts: 19
ICV valve bypassed=engine dies

Vehicle: 1984 911 Cab.

Following the manual I was looking for an increase in RPM with the ICV disconnected. I did NOT have that result, when the ICV was disconnected the engine quickly died.

Also in an attempt to set idle I jumpered the test ports and the same result, engine dies. Can't say I was surprised, because from what I understand that jumpered setup disables the ICV.

I am fighting a high (1100RPM) as well as a surging idle, also engine will die sometimes if while in idle you press the gas and quickly let off the pedal. The car just dies, you have to modulate how you let off the gas pedal in order for it not to die.

I have checked all sensors with a multimeter and all check out, the throttle body screw is 3 full turns out from fully closed. The car has new speed/reference sensors, the newer style CHT and new coil/plugs/cap/rotor and plug wires.

A smoke test has revealed a small leak between airbox/MAF (which shouldn't mater much, metered air) still fixing it though. I also have what appears the be a small leak comming from where the throttle linkage attaches to the left hand side of the throttle body, where it "goes in" to move the butterfly valve.

One thing to note is that when I remove the oil filler cap while the engine is running the RPM does not change at all indictating a vacuum leak, but man I having trouble finding it.

I have cleaned the ICV and it buzzes with igniton on, still need to bench test it with a battery. But what would cause the car to die with this unplugged/jumped?
Thanks for any help!


Last edited by Cubieman; 12-09-2019 at 06:31 AM..
Old 12-09-2019, 06:04 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered
 
Join Date: Oct 2016
Location: San Jose, CA
Posts: 566
Garage
Make sure the switch that tells the ECU that your throttle is closed is adjusted properly. You should hear it click when you open/close the throttle plate manually. If it's not telling the ECU that the throttle is actually closed then the idle behavior will be very erratic, at least that was the case with my car.

edit - guess I should have read more closely, sounds like you already checked the switches on the throttle body with the volt meter... sure does sound like a vacuum leak somewhere if the oil cap doesn't change the RPM at all.

Bill

Last edited by wjdunham; 12-09-2019 at 08:46 AM..
Old 12-09-2019, 07:04 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Registered
 
Join Date: Dec 1999
Location: Novato, CA
Posts: 4,707
Best advice: take it to a reputable shop and ask if you could watch how the pro does it. Surprising how much you can learn in such a short time, unless of course, you are a glutton for punishment and have nothing but time on your hands.

Cheers,
Joe
87 Carrera
Old 12-09-2019, 07:31 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
Join Date: May 2019
Posts: 19
I've got a nice heated garge with a 4 post lift so I'd like to think I can do it all. However I don't have some of the tools of the trade like a scope or an AFR meter. And I am an amateur mechanic at best.

Might be time for the pro to take over.

I also want to add that I checked the ECU harness to make sure all those signals were getting to the computer and my multimeter tests were all good. Also the ECU is a rebuilt unit from ECUdoctors.com, replaced in 2013. Hopefully that is good...

But does anyone have a theory to why when ICV is bypassed with the test port the car dies?

Last edited by Cubieman; 12-09-2019 at 10:35 AM.. Reason: Update Statuses
Old 12-09-2019, 10:10 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Registered
 
nene's Avatar
 
Join Date: Apr 2013
Location: Sonoma, CA....Wine Country
Posts: 670
Garage
Cubie,

Where are you located?

Serge
Old 12-09-2019, 01:22 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Registered
 
Join Date: Jan 2019
Location: Montgomery Tx
Posts: 1,638
Garage
I’ve seen vacuum leaks that don’t present themselves under low positive pressure(smoke tester) but are present under negative pressure (engine running).
I would carefully try spraying carb cleaner around the intake gaskets and throttle body shafts and see if the rpms increase.
Tony
Old 12-09-2019, 01:40 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
That Guy
 
Techno Duck's Avatar
 
Join Date: Mar 2003
Location: San Diego, CA
Posts: 4,879
Garage
It could be the idle bypass screw is not set correctly. It could be allowing too little air in to idle the engine when the ISV is disabled (shut)... the ISV is masking this when its operating.

Try opening it a little (turn counter-clockwise) and see what happens. Count how many turns so you can put it back if needed.
__________________
Jon
1988 Granite Green 911 3.4L
2005 Arctic Silver 996 GT3
Past worth mentioning - 1987 924S, 1987 944, 1988 944T with 5.7L LS1
Old 12-09-2019, 02:28 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Registered User
 
Join Date: May 2019
Posts: 19
I am in Lincoln,NE and have all winter to mess around with the car.
We have 1 porsche mechanic about 20 minutes away and a dealer 45 minutes away. I am hoping to lick this one, I am stubborn that way. Although I am no pro and I'm sure a porsche guy could find out more in an hour than I have in a month.

I will try your suggestions tonight.
Old 12-09-2019, 03:16 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Registered
 
Join Date: Jul 2017
Location: Australia
Posts: 25
On my 87 3.2 I had no detectable change in idle when removing the oil filler cap and like you did a smoke test and found no leaks except some slight smoke at the AFM/Air Filter box and some at the throttle shaft as well (very minor). I did have some surge at idle and hesitation sometimes. All very similar symptoms to you. My ICV did work however and I could jumper the test port and adjust idle to 880 RPM.
The problem was identified when I put a wide band AFR on the exhaust and saw that at idle I was super rich (10:1). Removing the oil filler cap leaned the mixture out to a normal type AFR (13-14:1) which didn't affect the idle speed that I could notice by ear. Adjusting the bypass screw had no effect after screwing it out about 7 turns in attempt to lean it out so I ended up having to alter the spring in my AFM by a few notches which showed signs of previous tampering. Idle mixture of 14.2 to 1 was achieved with the adjustment screw about 1 1/2 turns out and taking the oil filler cap off means the idle stumbles and the mixtures lean right out. Mixtures were checked carefully right up to redline at full throttle and were spot on at 13:1 richening up to 12.5:1 at redline. The car idles beautifully now and is super crisp to drive part and full throttle.
I think as a minimum first step I would take out the ICV and clean it and bench test with a power supply to make sure it moves freely. Check your fuel mixture at idle with a wideband AFR gauge and ensure you're not super rich or lean. Maybe your ICV is at its limit to control idle because the mixture is way out and disconnecting it means the engine just dies.
__________________
Davin
'87 Carrera 3.2
'66 VW Camper
'59 VW Beetle
Old 12-09-2019, 03:21 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Registered
 
Join Date: Sep 2013
Location: Eugene OR
Posts: 409
Garage
The jumper is supposed to center the ICV so you can adjust the screw on the throttle body, I bought a wide band 02 sensor and guage put some clips on the power leads and installed it in the 02 sensor hole to adjust the CO levels. Now itís part of a tool collection for my pre OBD cars. While you are messing with idle and CO adjustment you want the 02 sensor disconnected from the brain anyway.
Old 12-09-2019, 04:07 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Registered User
 
Join Date: May 2019
Posts: 19
Thank you guys so much for the responses, all great information!
I removed the ICV and bench tested it and it would open/close w/voltage applied. The idle screw was 1&1/2 turns out originally. I said 3 turns in my previous post, but that was half turns...

Anyways I turned out the T.B. screw 3 more full turns and I can now jump the ICV via the test port and the car stays running! Good or bad, a result. Also, the idle doesn't dip/stall out when pressing the gas pedal and letting off quickly as it did before.

Another effect turning out the T.B. screw had was there is a LOT more (white) smoke comming out of the tail pipe as well as more water being spit out. I may need to buy a wideband gauge to go any further on my own from the sound of it. I'll mess with it more tomorrow as I'm sure my next door neighboor my not care to hear a sport muffler at 10pm!
Old 12-09-2019, 06:57 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #11 (permalink)
Registered
 
T77911S's Avatar
 
Join Date: Oct 2006
Location: MYR S.C.
Posts: 13,676
pull a vacuum on the hose and brake booster to check for vacuum leak.

make sure the ICV vibrates with key on and engine off
__________________
86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 12-10-2019, 02:51 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #12 (permalink)
 
Registered
 
Join Date: Dec 2010
Location: Vancouver B.C.
Posts: 218
My 3.2 was experiencing a multitude of idle related problems . I performed all of the tests ,AFM , idle switch , CHT , CO 2 etc . I bench tested the ICV and it checked out good . It was suggested to me to block the flow of air to the ICV so I carefully clamped off the top hose to the ICV and to my surprise my car ran perfect !! I then removed the top hose and with the engine OFF and the ignition ON I discovered that the ICV was fluctuating and letting the intake air bypass creating an intermittent lean condition . After installing a new ICV my car has never run better . I hope this helps .
Scott .
Old 12-10-2019, 06:44 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #13 (permalink)
Registered User
 
Join Date: May 2019
Posts: 19
The ICV does buzz/vibrate when the ignition is on. I did do a vacuum test, I tapped into that Tee just to the left of the venturi, not sure what that line goes to.
With the engine running it was around 13-14hg on the gauge.
Old 12-10-2019, 06:47 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #14 (permalink)
Registered
 
Join Date: Dec 2010
Location: Vancouver B.C.
Posts: 218
When I bench tested my ICV I used a 9v battery as my power source and the ICV worked fine but with the 5v supplied by the harness it failed .
Old 12-10-2019, 08:11 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #15 (permalink)
Registered User
 
Join Date: May 2019
Posts: 19
So you ended up getting a new ICV I would assume? Man those are pricey.

Old 12-10-2019, 09:02 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #16 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 06:33 AM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2020 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.