An Idle question
05-20-2019, 05:46 PM
#1
Instructor
Thread Starter
An Idle question
I have three idle issues that I think MAY be related (on a 87 924S)
1- When I first start it up cold the idle is a little bit rough, just enough to get the hood to shake. Shows as 850 rpm on the tach (I seem to remember double checking this with another tach). Warm, it smooths out considerably.
2- At night the headlights very slightly dim/brighten on about a 1-2 second cycle. Only noticeable when sitting behind someone at a light, reflecting off the car in front, not when moving. (thinking of wiring in a relay kit)
3-Turning A/C on and off I notice a drop of rpm ( 50-100 rpm?) with it on. The idle gets slightly rougher at the same time.
Could these all be related ? Would the "Idle Speed Adjuster" cause these symptoms by allowing the load to affect the idle? I did clean it and check it buzzed a few years ( and very few miles) back. One of the few things I haven't closely checked or replaced (along with the O2 sensor).
1- When I first start it up cold the idle is a little bit rough, just enough to get the hood to shake. Shows as 850 rpm on the tach (I seem to remember double checking this with another tach). Warm, it smooths out considerably.
2- At night the headlights very slightly dim/brighten on about a 1-2 second cycle. Only noticeable when sitting behind someone at a light, reflecting off the car in front, not when moving. (thinking of wiring in a relay kit)
3-Turning A/C on and off I notice a drop of rpm ( 50-100 rpm?) with it on. The idle gets slightly rougher at the same time.
Could these all be related ? Would the "Idle Speed Adjuster" cause these symptoms by allowing the load to affect the idle? I did clean it and check it buzzed a few years ( and very few miles) back. One of the few things I haven't closely checked or replaced (along with the O2 sensor).
Last edited by maint; 05-31-2019 at 01:39 PM. Reason: shortened
06-05-2019, 07:19 PM
#6
I had persistent idle quality issues on my 924S. Turned out the intake gasket on cyl 3 had shrunk enough to draw air. Easy to verify, just shoot each intake to head runner with carb cleaner, if rpm picks up, you have a winner (or leaker). And yes, all issues are related, to idle speed.
06-06-2019, 10:27 PM
#7
Instructor
Thread Starter
I'll try that, or maybe a propane torch with a small hose attached to pinpoint if revs go up. Had the intake off and lots of "while you're in there" things got checked a couple of years back but it has mostly been parked until recently.