1G Idle and boost low

[Jacob Ritenour]

I picked up this 1991 Talon TSi in very rough condition it was basically a Flintstones car when I got it. It wasn’t running and was missing the fuel system, intake, turbo, and cooling system. I’ve since installed all of that, and now the car cranks and starts right up. In fact, it actually feels stronger than my 2G DSM with fewer miles.

Known Modifications Before I Got It (Only one's that could possibly contribute to the problem)​

• Aftermarket Magnus intake
• EGR delete
• Previously ran a 57mm turbo with a large FMIC
• Stock blow-off valve still in place
• I’m unsure if it was ever properly tuned (and it is not running an EPROM ECU)

I’m confused how it was even running in that condition without tuning, especially with the larger turbo setup.

Idle Problem​

The car starts and idles fine initially

• Cold start idle: 1,000 RPM
• After a few seconds: drops to 800 RPM

after driving, the idle slowly increases

• After about 5 minutes of driving: idle rises to 1,200 RPM
• After more driving climbs to 1,500 RPM
• Eventually can reach 2,000 RPM at a stop

Things I’ve already tried:​

• Cleaned and inspected the MAF
• Ran the car with MAF unplugged (RPM still climbs)
• Unplugged the IAC (no change)
• Tried testing the knock sensor suggestion I saw online (no change)

At this point I’m not sure what direction to go next.

Boost Setup / Issue​

I also swapped the setup back toward stock using a donor 1990 TSi I have

• Removed the 57mm turbo setup
• Installed a stock 14B turbo
• Reconnected vacuum lines to the wastegate and boost control solenoid

Now the car builds about 8–9 psi of boost.
Since I don’t have experience with 1G DSMs, I’m not sure if 8–9 psi is normal for this setup, or if something is still wrong, or if this is related to my idle issue.

Main Question​

Are these issues possibly related, or am I dealing with two separate problems and what should I check next? Vacuum? I'm not sure how to do that or where to start.

Thank you for any help

 

[pauleyman]

Did you run a vacuum line straight to actuator or does the car still have a boost solenoid?

 

[Jacob Ritenour]

Did you run a vacuum line straight to actuator or does the car still have a boost solenoid?

It still has the boost solenoid and lines ran to it spilts off just like how the vaccum diagrams shows

 

[steve]

Did you still have the line with the restrictor pellet inside?

 

[Jacob Ritenour]

Did you still have the line with the restrictor pellet inside?

I’m unsure of what that line is you’re talking about do you have a picture or location of it?

 

[pauleyman]

It still has the boost solenoid and lines ran to it spilts off just like how the vaccum diagrams shows

Its likely closed which happens based on a poor running car, knock etc. Ecu pulls timing and will shut down the solenoid to lower boost on an attempt to protect the motor. Reset ecu and see what happens. I would also check condition of the knock sensor, fuel filter, Injectors and fuel pressure.

 

[Jacob Ritenour]

Its likely closed which happens based on a poor running car, knock etc. Ecu pulls timing and will shut down the solenoid to lower boost on an attempt to protect the motor. Reset ecu and see what happens. I would also check condition of the knock sensor, fuel filter, Injectors and fuel pressure.

Knock sensor looked melted almost and I replaced that with the one from the donor, the fuel filter is new and so is the pump, when I pulled the injectors they didn't look bad either I'm uncertain about pressure though. Would a way to test that be bypass the solenoid or should I not risk that? I'll reset the ecu by disconnecting the battery if that is what you mean. Should I look into timing as well?

 

[pauleyman]

Knock sensor looked melted almost and I replaced that with the one from the donor, the fuel filter is new and so is the pump, when I pulled the injectors they didn't look bad either I'm uncertain about pressure though. Would a way to test that be bypass the solenoid or should I not risk that? I'll reset the ecu by disconnecting the battery if that is what you mean. Should I look into timing as well?

What basic maintenance has been done? Plugs? Wires? New fuel? Check for leaks/boost leak test? Check ignition and mechanical timing? Check ICS and do an idle reset? Check for idle position switch and required grounds? TPS calibration? Compression and/or leakdown test?
What have you looked at? Fill us in.

 

[dwb]

Have you performed a boost leak test? How are you gauging boost pressure? Does it have stock fuel injectors, pump, and pressure regulator? Considering you are using a donor car, are they both manual trans?

Here's some common culprits for idle issues:
BISS improperly adjusted or leaking
Boost/vacuum leak(s)
Failed ISC
Idle stop switch improperly adjusted, not hooked up, or not receiving ground
Throttle cable too tight
FIAV malfunction
ECU issues (blown ISC driver chip or leaking caps causing corrosion and broken traces)
TPS malfunction or improperly adjusted

 

[Jacob Ritenour]

What basic maintenance has been done? Plugs? Wires? New fuel? Check for leaks/boost leak test? Check ignition and mechanical timing? Check isc and do an idle reset? Check for idle position switch and required grounds? Tps calibration? Compression and/or leakdown test?
What have you looked at? Fill us in.

Sparkplugs have been done and I know the previous owner did the wires. New not old dirty fuel. Used a smoke machine and did not see any leaks, had a exhuast leak before but that has since been fixed. Haven't checked timing or ignition. Idle position switch I just now read about and will check that. No callibration of the Tps and have not checked compression or leakdown. I have looked at the MAF, IAC, Knock sensor, vaccum lines.

 

[19Eclipse90]

I’m unsure of what that line is you’re talking about do you have a picture or location of it?

In one of the ports of the boost control solenoid, there is was originally a restrictor in place. This link shows a 2G solenoid, but same idea.

 

[Jacob Ritenour]

Have you performed a boost leak test? How are you gauging boost pressure? Does it have stock fuel injectors, pump, and pressure regulator? Considering you are using a donor car, are they both manual trans?

Here's some common culprits for idle issues:
BISS improperly adjusted or leaking
Boost/vacuum leak(s)
Failed ISC
Idle stop switch improperly adjusted, not hooked up, or not receiving ground
Throttle cable too tight
FIAV malfunction
ECU issues (blown ISC driver chip or leaking caps causing corrosion and broken traces)
TPS malfunction or improperly adjusted

I have not yet done a boost leak test yet. I'm gauging the boost pressure from tapping into FPR line. Stock injectors, maybe just a slighter stronger pump and stock pressure regulator. Yes they are both manual trans the donor is a 90 while the main is a 91.

 

[steve]

There's that but I was thinking about the restrictor pill that is inside the hose. I've been looking for a picture or diagram since it's one of those things that's hidden kind of like the check valve for the brake booster.

It's job is to limit how quickly the boost source from the turbo can fill the hoses for the wastegate so that the BCS can lower the pressure in said hoses when it opens and dumps air back to the port behind the MAF.

Without it the normal boost pressure from the turbo swamps the ability of the BSC to do anything and you wind up with the same as a hose from the J pipe/compressor housing directly to the W.G.

 

[19Eclipse90]

Whoops. I read, “in the line”, and it just didn’t click.

I don’t seem to recall seeing something in the line.

 

[pauleyman]

Whoops. I read, “in the line”, and it just didn’t click.

I don’t seem to recall seeing something in the line.

It's been so long since ive thought about that. Most if us ditch it all for a manual controller.

 

[steve]

So long that I can't remember where it was. I've quickly perused the DTM and the 91 FSM and the 3S TIM.
The 3S TIM alludes to the pill by showing a restriction in the line but doesn't actually describe it. I haven't looked in the 3S FSM cause I have other things on my plate.

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[Jacob Ritenour]

There's now a code 31 back. What's a good way to test the knock sensor?