2G Rich idle, poor high rpm and stuttering

[Flying Cowboy]

Hey guys, struggling out here with my 95 GST.

Car is running very rich on idle (idling 1200 rpm) and kind of misfiring. When it revs about 3-4k rpm, it stutters and backfire (and my wideband reads 1.10+ lambda). New spark plugs, no boost leak, new MAF, and a full rebuild on the motor. Running stock ECU, stock injectors, stock fuel pump, and a .50 turbo on it.

Car sat about 8 months, electrical systems are crazy and I don't know where to start looking.

Before I stopped the car for maintenance, it ran perfectly, with the same set up, but needed to stop it because the timing belt run out of position and the valves hit the pistons.

Now the car starts pretty well, but runs badly.

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[CanadianTalonTC]

If you did not adjust the BISS, more air = higher idle. There is a bunch of stuff you had to do that can affect the idle. Did you adjust the throttle cable? Have you ensured the idle switch position is correct via factory procedures? As well as I'd be resetting the BISS/ISC back to factory settings to start.

When did you do the last boost leak test? You sure there isn't any leaks at the BISS or TB shaft seals? Did you replace the o ring and shaft seals?

How much boost are you running? a .50 trim will easily hit fuel cut which it seems to be what you are describing. It's like hitting the rev limit. Running something like that on the stock ECU is simply asking for trouble.

 

[BLACK'98DSM]

Sounds like the mechanical timing is off. Which would make sense, as this happened after installing new timing components. I'd be checking all timing marks.

 

[Flying Cowboy]

If you did not adjust the BISS, more air = higher idle. There is a bunch of stuff you had to do that can affect the idle. Did you adjust the throttle cable? Have you ensured the idle switch position is correct via factory procedures? As well as I'd be resetting the BISS/ISC back to factory settings to start.

When did you do the last boost leak test? You sure there isn't any leaks at the BISS or TB shaft seals? Did you replace the o ring and shaft seals?

How much boost are you running? a .50 trim will easily hit fuel cut which it seems to be what you are describing. It's like hitting the rev limit. Running something like that on the stock ECU is simply asking for trouble.

Hey, thank you for the tips, but turned out the new MAF was malfunctioning.

Anyway, i am running about 27 psi. Stock ECU and injectors are dealing with it pretty well til now

Still stuttering when WOT (but it seems a ignition problem) and very rich when throttle is out (when it should cut off the fuel).

But the idle problem is solved: bad new MAF

Wondering if TPS could be bad too.

 

[dwb]

Anyway, i am running about 27 psi. Stock ECU and injectors are dealing with it pretty well til now

Still stuttering when WOT (but it seems a ignition problem) and very rich when throttle is out (when it should cut off the fuel).

Turn your boost down. That's WAY too much for a stock fuel system. 15psi would be more realistic.

Also, please fill out a vehicle profile: https://www.dsmtuners.com/dsm-profiles/categories/2g-dsm.2/add

 

[CanadianTalonTC]

Hey, thank you for the tips, but turned out the new MAF was malfunctioning.

Anyway, i am running about 27 psi. Stock ECU and injectors are dealing with it pretty well til now

Still stuttering when WOT (but it seems a ignition problem) and very rich when throttle is out (when it should cut off the fuel).

But the idle problem is solved: bad new MAF

Wondering if TPS could be bad too.

Either your WOT A/F is lean af or you don't have a 50 trim running 27psi on stock injectors and ECU. No wonder there are so few of these cars left.