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Date:         Wed, 27 May 1998 10:04:58 -0700
Reply-To:     Mark McCulley <raven@HALCYON.COM>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         Mark McCulley <raven@HALCYON.COM>
Subject:      Re: 88 Syncro / cold start surging
Comments: To: Randolph Feuerriegel <RFeuerriegel@BC.SYMPATICO.CA>,
          Vanagon@VANAGON.COM
Content-Type: text/plain; charset="us-ascii"

At 01:12 AM 5/27/98 -0700, Randolph Feuerriegel wrote: >Greetings! New to the list, but have browsed & enjoyed the archives. >After months of trying to find a solution to my cold start surges from >numerous technicians, list archives, manuals, and trial on error, I am >hoping that someone on the list has had a similiar problem. I found one >list message about adding a 500 ohm resistor to the temperature sender >II which would fool the ECU into thinking it was warm. Did not try this.

This would be a band-aid that covers up the problem, not corrects it. I wouldn't recommend this as a long-term solution.

> The symptoms: Cranks over right away in the morning. About 30 sec to a >minute later it surges to 1500 rpm, then drops to 950 rpm. 30 secs later >another surge, then once more. If I let the vehicle sit until noon as >the day warms up, hardly a surge, and if it is really hot outside, no >surging. >Checks & replacements: New temp. sender ll. Measures up fine. Throttle >switch new and working fine. Idle stabilizer hums etc. & ICU swapped >with working others, still no change. Throttle shaft has a litle wear, >but the problems appears temperature related.

Have you checked thoroughly for vacuum leaks? Maybe you have a small vacuum leak that affects cold idle but is compensated for when the O2 sensor warms up. From my observations, the O2 sensor is ignored by the ECU for the first minute or two of operation from a cold start. Or maybe it's an intermittent vacuum leak that goes away when the engine warms up and parts expand.

>Grounds checked & >rechecked. Wiring ok, but just in case tried another FI harness. No >change. AFM swapped with working one, no change. Even tried the >capacitor in the AFM harness. Oxygen sensor fairly new and as it heats >up the surging stops. Van runs reasonably well after this.

It might be helpful to hook up a voltmeter to the output of the O2 sensor (leaving it connected to the ECU) and see what happens during the first couple of minutes of operation, especially when the idle speed surges. This could tell you whether the idle surges as the result of a leaner mixture or not. You can also measure the "dwell" on the idle stabilizer to determine if it's causing the rpms to surge. The Probst book details how to do this.

> There are a few other problems, intermittent rough idle, occaisional >missing at speed under 100 km per hour, some roughness from engine when >downshifting, back pressure. Over 100 km per hr., cruises just fine. >Lots of power. Have also replaced the coil, ignition wires, dist. & cap, >plugs. Beginning to think ECU. Hope not. Thanks for reading.

What exactly do you mean by "back pressure?" Is your catalytic converter shot? If so, you'll have to fix this before attempting to fix any of the other problems.

For comparison purposes, I just went outside and started my 87 and observed the rpms. Outside temperature was about 45-50F. Interestingly, I observed three distinct surges (just like you observed) in the first minute or so. However, the surges topped out at 1100 or 1200 rpm. After each surge, the idle slowly dropped back to 950 or so. My theory is that these surges occur when the ECU reaches transitions in how it calculates injection and timing paramters as the engine warms up. The idle stabilizer then does its job and drops the idle back down. Here's exactly what I observed on my 87:

At start idle is initially 1800 and then drops to 950 20 sec after start idle jumps to 1100 and then drops to 950 45 sec after start idle jumps to 1200 and then drops to 950 65 sec after start idle jukmps to 1200 and then drops to 1000

Hope this helps a bit. Good luck,

Mark McCulley


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