Hi, zli944 Bay Area, CA with a '94 FD.

The issues I have seem common but the intermittent nature of them is what has me stumped.

1. High idle RPM, around 1K to 1.2K upon the first start up of the day and rough idle. Some smoke from the pipes and what sounds like detonations (popping from the exhaust).
After driving around, it will drop below 1K, to what I think is 750, and seems to idle smoothly but it's barely above that second line on the tachometer, so it makes me think it's actually lower. I am not sure.

I've noticed also that during that initial start up, it doesn't matter how long I let it idle, it never drops below 1K until I actually drive the car around. And when I do drive it around, initially, dropping out of gear into neutral, the engine will surge slightly between 1K and 1.2K for a few seconds before settling.

These issues disappear after I drive around for 10-20 minutes.

2. Only happened ONE time for the FIRST time the other day. Accelerating in second, at exactly 3K RPM there was a stutter. Felt like the fuel pump cut out. It didn't happen the rest of the trip.

3. Low oil pressure readings. I know the senders are apparently very spotty so that could be it. I took the car to PR Motorsports in Hayward, CA and had them check the sender and they said it was working fine. So I don't really know what to believe. I still think it's the sender since I am getting regular readings sometimes and near 0 readings others... but until I save up for some new oil pressure gauges, I don't know for sure.

4. No boost from second turbo. This could be a billion things, I'm only putting this in here as a reference and maybe a clue for more knowledgeable members to put together with the other issues. 10-0-0 boost pattern.

The car itself:

It has around 80k miles and as far as I can tell, was completely unmodified till I got it last 2015 December.

I have only done the following mods:

RB Catback
HKS Downpipe
Boost Gauge

Recently replaced the clutch, read main oil seal and stat gear o-ring.

There are definitely oil leaks from the pan and turbos but since the rear main/ stat gear changes, I'm not bleeding the stuff anymore.

Thanks for your time.

 

1/2) Your RPM issue could be caused by intermittent signal coming from the Crank Angle Sensors. My FD had a similar idle issue (a little more consistently but similar fluctuations). In my case it was the wiring going to the G CAS that was losing connection when the engine was either very cold or at operating temperature. In your case i would be more prone to say that it would be a connector issue since your car isn't dying on you and the issues disappear after running for some time. Otherwise, it may be worth looking at your IAC solenoid on the back of the extension manifold to see if it is sticking at all.
3) As for the oil readings my money would also be on the pressure sender or the wiring to it as both are relatively flimsy and there are few other failures that would cause that issue without other more serious issues also popping up.
4) The turbo is odd. I am no expert on them but possibly your second turbo has seized from carbon build-up? If the CAS is the cause of the idle issue it could be related to the turbo as well but I would say that it is unlikely.

 

that's pretty interesting you'd mention the CAS connections
during the clutch install we also did the motor mounts and moved the engine around quite a bit. I was worried bout the electrical connections coming loose since I didn't bother disconnecting any of them... so maybe that actually happened.

and of course, the IAC. I definitely had that on my check list but forgot all about it, so many damn bookmarks.

the second turbo... I know I should troubleshoot, but i've got a set of 99 spec turbos and am part of that azeknightz rack GB. so instead of troubleshooting, i plan on just replacing everything

I'll check the IAC and CAS and update! Thanks man.

 

*update* but not the good kind. drove the car around last night and idle was surging a little even after being warmed up. Then this morning, the ADD COOLANT buzzer and light came on when I was starting the car...
I plan on flushing the system and really really hoping it's not a blown water seal (I don't think it is since I'm not seeing anything out the pipes)

 

Quick update in case anybody runs into this issue in the future:

The Idle Issue:

An CEL finally popped up and I got code 11, which is the IAT. I replaced it with the fast reacting one that that one guy (forget his name but just search fast reacting IAT) sells and it's pretty much solved a lot of the rough idle issues. Detonations are still there occasionally and AWS is still somewhat in effect, but it drops idle MUCH more quickly and idles very smoothly. (detonations still occur during deceleration sometimes but I hear that might just be a rotary thing and because I have the catback in)

The Boost Issue

I think I've narrowed it down to the precontrol/wastegate solenoids. It holds steady at 7 PSI boost to 4.5k RPM which I hear is what'll happen if those solenoids are actually disconnected (thought IIRC, they should be doing that with the second turbo too...) I haven't tested this because I'm scared of unintended consequences but I figure it's worth a shot.

 

Before spending $100 + on a new oil pres. sender you might try just cleaning that single spade connector. It's right under the oil filter pedestal and tends to get dirty over time. At idle and low rpm I think the signal is weak and can't get thru a poor connection...showing up as low or no indicated psi that suddenly jumps with rpm.