engine diagnosis help needed
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Track Day
Joined: Jul 2004
Posts: 22
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From: Ann Arbor Michigan
engine diagnosis help needed
I need some help diagnosing a 928, nobody who looks at it has the slightest idea what the problem is. Here are the symptoms I've noticed.
-'85 S3
-significant idle wander at startup (200-1800rpm cycles)
-3mph wander in cruise control
-throttle surging, sometimes even shuddering under acceleration
-low on power
and starting today on my way to work in the rain the engine started periodically running extremely rough - way down on power and became hard to drive. it felt like the plugs were fouled but being somewhat intermittant I couldn't imagine that.
I've gone through looking for vacuum leaks, manifold is vacuum looked fine to me. None of the mechanics have been able to find the problem either.
Any help would be desperately apreciated!
Thanks
Joe
-'85 S3
-significant idle wander at startup (200-1800rpm cycles)
-3mph wander in cruise control
-throttle surging, sometimes even shuddering under acceleration
-low on power
and starting today on my way to work in the rain the engine started periodically running extremely rough - way down on power and became hard to drive. it felt like the plugs were fouled but being somewhat intermittant I couldn't imagine that.
I've gone through looking for vacuum leaks, manifold is vacuum looked fine to me. None of the mechanics have been able to find the problem either.
Any help would be desperately apreciated!
Thanks
Joe
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From: Anaheim California
Quite possibly it was running on 4 cylinders when you were experiencing the very low on power and rough. Any issue with either of the two ignition systems ...coils ,coil wires, caps rotors, ignition switching (secondary stage) units could cause such a dramatic loss of power and roughness. The hot wire mass air flow sensor may have degraded so that you air fuel ratio is way off as well . It is also possible that the L H injection brain is not processing information correctly. Unfortunately more questions than answers.
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From: Rochester, WA
Originally Posted by marc@DEVEK
Check vacuum, sounds like a leak....maybe intake gaskets?
Marc
Marc
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From: Norfolk, VA
Sounds like an issue I had with my 86. Could be Mass Air Flow sensor. I had the exact same issues...with the exception of the cruise....that could be an issue with the cruise control brain. My car would run fine.....then run like crap...then would run normal. I ended up fouling out the plugs trying to keep the thing running. When I disconnected the Mass Aif Flow, the car would run...when it was attached it would not run unless I nursed the gas peddle. I did all the test in the shop manuals and the MAF tested OK.....yet it was still bad.
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Thread Starter
Track Day
Joined: Jul 2004
Posts: 22
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From: Ann Arbor Michigan
thanks
Thanks everyone for your input.
I'm going to take the car to the dealer next week and specifically ask them to look at the MAS.
Does anyone have a sure fire way to test for vacuum leaks on these? I've used my vac guage to try and isolate a problem but without luck. Tried the butane and hose technique also to no avail.
Also, how often do people generally go through plugs and wires? Any suggestion on brands? My caps, Rotors and T-belt are new other than that I have no idea since I havn't had the car that long.
Thanks again for all the great help!
Joe
I'm going to take the car to the dealer next week and specifically ask them to look at the MAS.
Does anyone have a sure fire way to test for vacuum leaks on these? I've used my vac guage to try and isolate a problem but without luck. Tried the butane and hose technique also to no avail.
Also, how often do people generally go through plugs and wires? Any suggestion on brands? My caps, Rotors and T-belt are new other than that I have no idea since I havn't had the car that long.
Thanks again for all the great help!
Joe
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From: Mountains of GA!
Originally Posted by jlambert
I'm going to take the car to the dealer next week and specifically ask them to look at the MAS.