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Need Info Regarding A Tough Rough Idle

SargeRX8

By SargeRX8,
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SargeRX8 Grand Master

SargeRX8

Posted
Posted

Hey all,

Its been some time since I've posted here but I'm at it now and I need some direction. This ones got me stumped.

My car has, for quite some time now(more than a year), been idling poorly. In a nut shell.

In more detail, the car will never start first go in the morning unless I'm lucky and mashing the throttle or its a warm/hot day. No idea if this is related but lets move on. When my car does start and run while its cold, its perfect, revs hold fine until it warms and they come down to the normal range. I can then go on my drive, 5 minutes to 1 hour what ever it is and more often than not my revs will not be stable. If I watch the needle closely I can see the needle jitter as well as hear it in the engine and see it in the vacuum gauge.

Today it was significantly worse. My car pulls a nice high amount of vacuum, usually at -28 to -30 on my boost gauge and -96 on my Profec B spec 2. Today it decided to pull between -20 and -24 and -76 and my revs came down to about 700 and were fluctuating between 700 - 780. It was audibly noticeable. I thought I may have popped off a hose or something so I pull over and listen over the whole engine bay and it sounded just fine. I gave it throttle and there was no sign of boost leak either.

I really don't know where to go with this. I do not run a O2 sensor and my car has all the bolt ons(mods below). I have no idea where to go from here. I don't know if this is a vacuum leak since it doesn't happen all the time. Another thing to note is I have ran 100octane E10 fuel from United over at Drummoyne. That stuff is awesome. I know people hate it but I've ran probably 3 tanks of that stuff and I get more KM's and it seems to kick my knock out the window.

The AAC valve has been cleaned, the plenum gasket is fresh as the old one busted out. The TB to plenum gasket is fresh. I need a second set of ears as I suspect there MAY be a leak somewhere under the plenum but for the life in me I can not locate where the sound is coming from and spraying gas in the area does not cause the revs to change. If anyone can make any suggestions as to where I can start looking with this, that would be great.

Also to throw this in there, the other day when I started my car in the morning the engine light came on for about 3 seconds and the moment it came on I heard a lean pop from the exhaust. I have no idea what caused the light to come on. It has happened once in the past for about 3 seconds while driving and during that 3 seconds the car ran like absolute dog shit.

The car is an R33 GTST with the following:

Unopened RB25DET

Power FC

740cc nismo injectors

Z32 afm

HG SS2

3" to 4" exhaust

Enclosed Pod

Thanks all!

Ben C34 Grand Master

Ben C34

Posted
Posted

Check for vacuum leaks.

Easiest way is by pressure testing. Then you can hear the leak and spray soapy water if needed to make it even easier to find.

Have you ever checked the timing?

AngryRB Grand Master

AngryRB

Posted
Posted (edited)

sounds like what I experienced with mine, the intake manifold is warped and would never seal properly, squrt some carby cleaner on the plenum gasket and see what happens, mine was playing

games with me cause it seemed to run ok but then at times it would just stall when starting or reversing, also when I converted to E85 the cold start was too lean and gave stalling when cold.

Edited by AngryRB
SargeRX8 Grand Master

SargeRX8

Posted
  • Author
Posted

I haven't checked the timing since it was done nearly two years ago as I don't have a timing light. Part of me thinks it may be something to do with the CAS but I don't know if a CAS issue wil throw a check engine warning.

I'll do a pressure test this weekend after I make a new jig. I can't find the old one.

I really hope its not a warped anything. I'm gonna go over it again and tighten everything around the plenum up, I remember changing the gasket there and the thing was an absolute bitch to do and it was summer. Maybe I didn't apply enough tension to a screw.

I don't know how to determine if the check engine light is related to this issue since the check engine has only happened twice in about 3 - 4 years of owning the car.

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