Rough idle when engine cold

A couple of more items about the car that I found in the little documentation that I have
Turbo is a 6680 GTQ Precision Turbo
Power plate ?
Fuel pump and hot wire (no idea on model of fuel pump but assume after market)
Unfortunately the company that did the work is no longer in business so I cant get any details.
 
I found a hose unplugged. Its the one that I think is supposed to plug into the charcoal canister and from there goes to the fuel tank and acts as a vent. Is it o.k if its not plugged into the charcoal canister ?
 
So far have cleaned MAF, Throttle body, IAC, new plugs. still same problem. Starts up fine when cold, runs for about a min or so then just dies unless I feather the gas. Once warmed up all is good. Shall I try replacing my IAC ?
 
rhturbo said:
So far have cleaned MAF, Throttle body, IAC, new plugs. still same problem. Starts up fine when cold, runs for about a min or so then just dies unless I feather the gas. Once warmed up all is good. Shall I try replacing my IAC ?
Click to expand...
I would change the O2 sensor. When I bought my '87 GN it had the same problem. Turned out to be a bad O2 sensor.
 
mikestertwo said:
I would change the O2 sensor. When I bought my '87 GN it had the same problem. Turned out to be a bad O2 sensor.
Click to expand...

When the car is cold it is running off a fixed table and isn't looking at the O2 sensor. Once it reaches the coolant temperature threshold to go closed loop it will reference the O2 to make fuel trim adjustments.

Did you ever determine what chip is in the car?

Neal
 
rhturbo said:
If it was an O2 sensor would it not cause a service engine light ?
Click to expand...
No unless the sensor is stone dead. If the sensor is contaminated and slow giving a wrong reading the computer doesn't know that. If the readings are inaccurate the computer will adjust the fueling incorrectly.
 
I haven't checked on the chip yet. I wont be able to do anything else for a couple of weeks. I will check it then
 
It seems to me you said you have 60# injectors and the chip is labeled as being for 50's. If this is true the injector constant that is part of the chip programing is not correct for the injectors in the car.

Neal
 
I have this same problem. I have tried a few different things. I have other issues with my car too but a MAF is my next step. I'm going to invest in a translator and a LT1 MAF and see where that gets me. Not sure if that helps you at all but that is where I am at, I have not been able to find any vacuum leaks on my car and I am still messing around with setting but like I said that is where I am headed, in part, just to replace the crappy stock MAFs.
 
Recap of my issue. When I start the car it starts right up and ran fine for about 2 mins as usual. I kept an eye on the fuel pressure gauge and it was steady at around 40PSI. Then it starts to surge and hunt up and down and the idle is all over the place. Eventually stalls like its running out of gas. Starts right up again though with no issues but still runs rough for a couple of mins and i have to give it gas to keep it running. Once warmed up it runs fine but there is still some slight fluctuation with the idle. It floats around between about 750 - 850 RPMS.

One other thing I should mention. I am only assuming it has an after market cam in it because it came with a bucket of original parts with the original cam being one of them.
 
Sounds to me it is the MAF causing this.
The wire is heating up in the MAF and the not-as-hi vacuum that the factory cam produce is leaning the engine out to much.
The best way to fix this is get a translator and an LT-1 MAF and set it as the instructions say for the cam you have.
 
With engine running I would set tps to .42, iac to 15-20 range, fuel pressure to 43 psi with vacuum line off (and plugged) the fuel pressure regulator. Blm and integrator should be 128 +/- 10 with engine warm (and cold). Replace fuel filter located under driver's door. Kirban sells a stainless bracket if yours is rusted. If the car still isn't idling right I would get a turbo tweek chip. I doubt it's the maf.
 
Yesterday I disconnected the MAF and the car started up and idled with no issues. Does this point to a bad MAF ? MAF has been cleaned but didn't help
 
O2 change they are cheap, you can save the old one for testing if no change in drive-ability is found.

Get a new chip for the fuel (ocatane) you are using alky. no alky. etc.

If you will be getting a MAF translator soon, well that will be a given in MHO., get an extender chip or turbotweak chip that works with it.

You can clean and reset the IACV and have a looksee at the pintle for wear and dirt, but they rarely go bad.
 
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