Why Does My Engine Surge on Warm Start?
09-21-2007, 06:08 PM
#1
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Why Does My Engine Surge on Warm Start?
On cold start my 89 S4 cranks right up, idles evenly until warmup begins, then settles right down.
On a warm start, usually after sitting an hour or two, the engine engages, surges up a couple hundred rpm's, then drops to about 400-500 rpm, surges up to 700-800, then drops back down, etc. If I give it a little throttle, idle evens out, runs at around 750 rpm.
Idle resonance valve, throttle position sensor & reference mark sensor were replaced approx. 3000 mi. ago, along with an injector rebuild & new intake hoses & vacuum lines.
Is this a fuel quality problem? Sensor? It's not a huge issue, but annoying. Any advice is greatly appreciated.
Thanks,
Hawk
On a warm start, usually after sitting an hour or two, the engine engages, surges up a couple hundred rpm's, then drops to about 400-500 rpm, surges up to 700-800, then drops back down, etc. If I give it a little throttle, idle evens out, runs at around 750 rpm.
Idle resonance valve, throttle position sensor & reference mark sensor were replaced approx. 3000 mi. ago, along with an injector rebuild & new intake hoses & vacuum lines.
Is this a fuel quality problem? Sensor? It's not a huge issue, but annoying. Any advice is greatly appreciated.
Thanks,
Hawk
09-21-2007, 08:16 PM
#2
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The quick and easy way to rule out a bunch of issues is to hook your '89 to a Hammer or Spanner.
Failing that, drag out Jim's CDs and find the LH/EZK diagnostic guide.
If the car didn't exhibit the warm surge behavior before the Idle Stabilizer, Idle/WOT switch, and reference mark sensor R&R then start by double checking the operation of the ISV and Idle/WOT switch. The latter must be positioned carefully and the throttle cable correctly adjusted or the idle part of the switch will be always "off." The behavior of your '89 is similar to that of my '89 - and I know it has a dead idle switch. There's a new one in a box on its passenger seat. Just haven't gotten to it yet.
If the car had this behavior before the items above were replaced then I would start with the Temp II sensor.
The above-mentioned guide on the CDs will provide all the details on how to test various things. All you need for most of the tests is a multi-meter and some jumper wires.
Failing that, drag out Jim's CDs and find the LH/EZK diagnostic guide.
If the car didn't exhibit the warm surge behavior before the Idle Stabilizer, Idle/WOT switch, and reference mark sensor R&R then start by double checking the operation of the ISV and Idle/WOT switch. The latter must be positioned carefully and the throttle cable correctly adjusted or the idle part of the switch will be always "off." The behavior of your '89 is similar to that of my '89 - and I know it has a dead idle switch. There's a new one in a box on its passenger seat. Just haven't gotten to it yet.
If the car had this behavior before the items above were replaced then I would start with the Temp II sensor.
The above-mentioned guide on the CDs will provide all the details on how to test various things. All you need for most of the tests is a multi-meter and some jumper wires.
09-23-2007, 04:07 AM
#4
I had very similar symptoms when I fitted the air filter element upside-down! When warm the revs would fluctuate over about a 500rpm range every 5-8 seconds and on occasion would drop low enough to stop the engine. Simple 5-minute check - run it with the filter out.
Colin. 89GT
Colin. 89GT
