1988 2.5l Rough Idle, Pressure in Crankcase (Page 2/2)
sbauco JUL 17, 11:28 PM
Plugs are basic copper AC Delco, R43TS6, with out-of-the-box stock gap.

When I bought the car it was actually missing the ICM shield, but thanks to your cave I knew I needed one! I didn't know where to find one, so I fabbed up my own out of steel.
Patrick JUL 18, 01:16 AM

quote
Originally posted by sbauco:

...the big question is: should I try and get the idle better, or is a slightly misfire-y stable idle about as good as it gets for a duke?



My first Fiero back in the mid 1990's was an '87 duke, basically the same engine as the '88 minus the balance shafts and weird oil filter location. I hated that engine. As you know, there's no way to change the ignition timing, and it's so freakin' advanced at idle. I had nothing but trouble getting that car to pass the smog tests. Did I mention I hated that engine?
sleek fiero JUL 18, 10:39 AM
hey how come nobody has suggested changing out the PCV itself as the can spoil a perfect tune all by themselves. they can get crudded up or the spring gets weak or broken. people don't realize the pcv actually sends a metered amount of crankcase gasses/air back to the throttle body to be burnt off and if the are not working properly can throw off your tune especially idle.
sbauco JUL 18, 09:19 PM

quote
Originally posted by Patrick:

My first Fiero back in the mid 1990's was an '87 duke, basically the same engine as the '88 minus the balance shafts and weird oil filter location. I hated that engine. As you know, there's no way to change the ignition timing, and it's so freakin' advanced at idle. I had nothing but trouble getting that car to pass the smog tests. Did I mention I hated that engine?


^This is exactly what it feels like! It feels like the timing is so advanced at idle that it's constantly on the edge of missing. Despite the idle RPMs being fairly stable now, the idle exhaust note has that airy, sort of lean sound to it, and the misfire rate is oddly high.


quote
Originally posted by sleek fiero:

hey how come nobody has suggested changing out the PCV itself as the can spoil a perfect tune all by themselves. they can get crudded up or the spring gets weak or broken. people don't realize the pcv actually sends a metered amount of crankcase gasses/air back to the throttle body to be burnt off and if the are not working properly can throw off your tune especially idle.


This is a good point; a new one is literally $2, so maybe I'll toss one in and see what happens. My current valve is pulling vacuum properly, but I could imagine that maybe the flow rate is reduced if there's a bunch of crap inside the valve.
sbauco JUL 18, 09:23 PM
Oh also, there's another weird symptom that I forgot to mention. Ever since I bought the car, the oil pressure gauge has been super wonky. It reads pressure properly at idle, but for some reason the gauge tends to randomly peg at maximum when I'm driving. Oddly it seems to especially like to to this when I'm off-throttle. I always assumed this was just a weird issue with the oil pressure sensor, but could this be indicative of broader electrical problems that could also be affecting the idle?
Patrick JUL 18, 10:22 PM

quote
Originally posted by sbauco:

It reads pressure properly at idle, but for some reason the gauge tends to randomly peg at maximum when I'm driving.



The oil pressure gauge will peg if the sending unit is disconnected. Check the connector for looseness.


quote
Originally posted by sbauco:

It feels like the timing is so advanced at idle that it's constantly on the edge of missing.



Just for "fun", put a timing light on there and see how far advanced the ignition timing is while idling. It's no wonder that engine won't idle smoothly.

You might find This ancient thread of some interest.

[This message has been edited by Patrick (edited 07-18-2023).]