Could this be a vacuum leak?

[KarlGTB]

I'm trying to diagnose a problem with my legacy that I've had for some time, and before I throw more money into the bottomless pit I'm wondering if someone might have experienced this or could help me out.

Car is a 1996 GTB with the EJ20R, which has been rebuilt with JE's and is still running the factory twin turbo setup. Only mods on it are straight through muffler.

Problem begins at start up. On a cold start it will rev to about 2000rpm for a couple of seconds then drop back to idle hunting between 600-1000rpm. Once driving (still with cold engine) it will struggle unless I keep the revs at or above 2000-2300, below that it feels like i'm lugging it, and changing gear sometimes it will stall. I can hear what sort of sounds like a sucking noise (but it could possibly be a rattling noise) until i reach that 2000-2300rpm point where the primary starts spooling up and then it goes away. I normally only drive it with partial throttle while its cold, but wide open throttle makes the effects worse.

Once warm its low rpm performance is a bit better, it wont stall, but the noise doesnt go away. I can also hear a slight whistling noise on primary boost but its not near as audible. Idle will still hunt but not to the same extent.

I recently had all the up/down/crossover exhaust gaskets done at great expence so wouldnt expect it the noise to be coming from the exhaust side of things.

Also no current CEL codes, but did have a 31 Throttle Position Sensor a few months back but cleared it and it never came back.

[dumbskate]

For that age I woudl be checking Thermostat for replacement, Idle control sensor (that may be the same as "Throttle Position Sensor" for a good clean, also fuel filter for replacement, and spark plugs/coil packs for cracks or replacements.

Usually the engine is rebuilt but the "bolt on" units are not serviced or cleaned at the same time.

[BC5RA]

Have you had the exhaust nuts re tightened?

[KarlGTB]

Thermostat was done at the rebuild 20,000km ago, plugs and coils done approx 10,000 ago, fuel filter was done about a month ago along with a new fuel pump. Ive had what I think is the idle control sensor off, but it looked pretty clean. Getting the throttle position sensor off looks a bit more tricky though. Would a go with some of this magical subaru upper engine cleaner be worth a try? Oh and no I havent had exhaust nuts retightened.

[log1call]

Sounds a lot like a blocked exhaust.

[Guest boostcut]

TO RULE OUT A VACUUM LEAK SPRAY CARB CLEAN OR BRAKE CLEAN AROUND ALL INTAKE GASKETS HOSES ETC AND LISTEN FOR IDLE CHANGE.

[KarlGTB]

Ok i'll have a go with the carb clean

 log1call said:

Sounds a lot like a blocked exhaust.

. I have had the cat converter light come on a few times in the past when the car has been loaded up on long trips, i wonder if i should get that removed.

[Guest]

Check engine vacuum at idle and let me know

The fault being worse when cold would indicate a lean issue so either the vac leak / coolant / airflow or MAP sensor issue