Help!! SW20 Acceleration and idle problem!

[Mr2zilla]

Hey guys a bit of troubleshooting needed!
I got a SW20 1992 with 3sgte, mostly stock other then air filter, exhaust, downpipe and running on 11psi boost which I just tweaked up from 7psi couple of weeks ago.
The other day went out for drive, revved high and boost was good however when I stopped at a petrol pump the cars idle was jumping from 1500 to 2000rpms but I turned the car off and started again the rpm stayed at 1500 and didnt dropped. When I got outta there noticed the car was making boost on the guage but wasn't pulling like before. Can notice when letting of the gas the boost compression surge is just a whoosh and car sounds a little bit quiter from the exhaust when boosting.
The car does run a bit rich since I bought it. The compression flutter was usually in 5th gear but in lower gears it used to sound like a bov (NO BOV, the outlet is blocked with a plate). No ides whats going on! is is like a leak or somthing serious??

[GDII]

Check all your turbo hoses and pipes for leaks. I'd say a hose has come off.

[Benckj]

Definitely sounds like and I take leak such as split hose. Even the original 1500 idle is high.

Starting with only 7psi boost shows there is also a problem with your stock control as should be over 10. Probably not a real concern since you have installed an aftermarket controller but an underlying issue all the same. There could be a number of protection measures that become bypassed. Can you explain your set-up a bit better including type on controller used, boost gauge and any other mods with pics?

[Mr2zilla]

Boost controller looks like a GFB atomic manual boost controller and gauge is a Prosport.
Also would like to mention there's a free wire connected to the engine hood and a sensor in the front near radiator dangling freely(Can somene pls tell what are these). Pls check the attached pics.

[GDII]

The engine lid wire should be plugged into the sensor next to it. However the only thing unplugging it like that does is make the intercooler fan run all the time. Some people like that.

The front is the temp sensor for air conditioning. It normally sits down inside the front grille next to the radiator.

With the idle, if you do have a leak, these AFM (Air Flow Meter) engines do not like vacuum leaks so any extra air that is not metered will cause extra air to be in the engine and cause a lean situation which can produce higher idle.

See if you can do a boost leak test and let us know the results.

[Alsw20]

Is your car running with the boost gauge just below 0?

If it is, that is defiantly a hose somewhere has a crack or come away.

If it's not, what does your warm idle show? Should be around 20 in.Hg, anything significantly closer to zero means boost leak.

[*84vvt]

Spray some engine start around the BOV plate , to see if the vacuum leak is there the plate looks to thin to do a good job at sealing off the port .

[Alsw20]

Spray some engine start around the BOV plate , to see if the vacuum leak is there the plate looks to thin to do a good job at sealing off the port .

Good idea. That is the hot pipe and the metals may expand at different rates.

[Mr2zilla]

appreciate all the replies guys!!
Ill try to check it out this weekend .(m still going to work under lockdown)

#Alsw20 the 0 reading was when the car is turned off. (guess gauge needs correction) . on Idle the reading goes around -25psi.

And i forgot to mention one thing that when that thing happened I also noticed boosting up was a bit quicker on the gauge.
however, the next morning and even today when I start the car the idle goes to normal after warming up. (after a small ride but car rides like its NA or has minimal boost while the gauge shows its going till 11psi)

[Mr2zilla]

Prob solved!! Found the turbo to inter-cooler pipe busted!! Temporary fixed it and went for a test drive!! All good now!

[GDII]

Good you found the problem. It seemed logical that it would have been a joiner based on your description. Might pay to think about replacing all the old rubber joiners in the future so it doesn't happen again. They are getting on 30+ years old.

[Benckj]

Good you found the problem. It seemed logical that it would have been a joiner based on your description. Might pay to think about replacing all the old rubber joiners in the future so it doesn't happen again. They are getting on 30+ years old.

.......and use proper torque clamps as they hold better than the standard hose clamps and don’t tear into the rubber.